/*      $OpenBSD: vfs_bio.c,v 1.217 2026/02/11 22:34:41 deraadt Exp $   */
/*      $NetBSD: vfs_bio.c,v 1.44 1996/06/11 11:15:36 pk Exp $  */

/*
 * Copyright (c) 1994 Christopher G. Demetriou
 * Copyright (c) 1982, 1986, 1989, 1993
 *      The Regents of the University of California.  All rights reserved.
 * (c) UNIX System Laboratories, Inc.
 * All or some portions of this file are derived from material licensed
 * to the University of California by American Telephone and Telegraph
 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 * the permission of UNIX System Laboratories, Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)vfs_bio.c   8.6 (Berkeley) 1/11/94
 */

/*
 * Some references:
 *      Bach: The Design of the UNIX Operating System (Prentice Hall, 1986)
 *      Leffler, et al.: The Design and Implementation of the 4.3BSD
 *              UNIX Operating System (Addison Welley, 1989)
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/buf.h>
#include <sys/vnode.h>
#include <sys/mount.h>
#include <sys/malloc.h>
#include <sys/pool.h>
#include <sys/specdev.h>
#include <sys/tracepoint.h>
#include <uvm/uvm_extern.h>

struct uvm_constraint_range high_constraint;
int fliphigh;

int nobuffers;
int needbuffer;

/* private bufcache functions */
void bufcache_init(void);
void bufcache_adjust(void);
struct buf *bufcache_gethighcleanbuf(void);

/*
 * Buffer pool for I/O buffers.
 */
struct pool bufpool;
struct bufhead bufhead = LIST_HEAD_INITIALIZER(bufhead);
void buf_put(struct buf *);

struct buf *bio_doread(struct vnode *, daddr_t, int, int);
struct buf *buf_get(struct vnode *, daddr_t, size_t);
void bread_cluster_callback(struct buf *);
int64_t bufcache_recover_dmapages(int discard, int64_t howmany);
static struct buf *incore_locked(struct vnode *vp, daddr_t blkno);

struct bcachestats bcstats;  /* counters */
long lodirtypages;      /* dirty page count low water mark */
long hidirtypages;      /* dirty page count high water mark */
long targetpages;       /* target number of pages for cache size */
long buflowpages;       /* smallest size cache allowed */
long bufhighpages;      /* largest size cache allowed */
long bufbackpages;      /* minimum number of pages we shrink when asked to */

vsize_t bufkvm;

struct proc *cleanerproc;
int bd_req;                     /* Sleep point for cleaner daemon. */

#define NUM_CACHES 2
#define DMA_CACHE 0
struct bufcache cleancache[NUM_CACHES];
struct bufqueue dirtyqueue;

void
buf_put(struct buf *bp)
{
        splassert(IPL_BIO);

#ifdef DIAGNOSTIC
        if (bp->b_pobj != NULL)
                KASSERT(bp->b_bufsize > 0);
        if (ISSET(bp->b_flags, B_DELWRI))
                panic("buf_put: releasing dirty buffer");
        if (bp->b_freelist.tqe_next != NOLIST &&
            bp->b_freelist.tqe_next != (void *)-1)
                panic("buf_put: still on the free list");
        if (bp->b_vnbufs.le_next != NOLIST &&
            bp->b_vnbufs.le_next != (void *)-1)
                panic("buf_put: still on the vnode list");
#endif

        LIST_REMOVE(bp, b_list);
        bcstats.numbufs--;

        if (buf_dealloc_mem(bp) != 0)
                return;
        pool_put(&bufpool, bp);
}

/*
 * Initialize buffers and hash links for buffers.
 */
void
bufinit(void)
{
        u_int64_t dmapages;
        u_int64_t highpages;

        dmapages = uvm_pagecount(&dma_constraint);
        /* take away a guess at how much of this the kernel will consume */
        dmapages -= (atop(physmem) - atop(atomic_load_sint(&uvmexp.free)));

        /* See if we have memory above the dma accessible region. */
        high_constraint.ucr_low = dma_constraint.ucr_high;
        high_constraint.ucr_high = no_constraint.ucr_high;
        if (high_constraint.ucr_low != high_constraint.ucr_high)
                high_constraint.ucr_low++;
        highpages = uvm_pagecount(&high_constraint);

        /*
         * Do we have any significant amount of high memory above
         * the DMA region? if so enable moving buffers there, if not,
         * don't bother.
         */
        if (highpages > dmapages / 4)
                fliphigh = 1;
        else
                fliphigh = 0;

        /*
         * If MD code doesn't say otherwise, use up to 10% of DMA'able
         * memory for buffers.
         */
        if (bufcachepercent == 0)
                bufcachepercent = 10;

        /*
         * XXX these values and their same use in kern_sysctl
         * need to move into buf.h
         */
        KASSERT(bufcachepercent <= 90);
        KASSERT(bufcachepercent >= 5);
        if (bufpages == 0)
                bufpages = dmapages * bufcachepercent / 100;
        if (bufpages < BCACHE_MIN)
                bufpages = BCACHE_MIN;
        KASSERT(bufpages < dmapages);

        bufhighpages = bufpages;

        /*
         * Set the base backoff level for the buffer cache.  We will
         * not allow uvm to steal back more than this number of pages.
         */
        buflowpages = dmapages * 5 / 100;
        if (buflowpages < BCACHE_MIN)
                buflowpages = BCACHE_MIN;

        /*
         * set bufbackpages to 100 pages, or 10 percent of the low water mark
         * if we don't have that many pages.
         */

        bufbackpages = buflowpages * 10 / 100;
        if (bufbackpages > 100)
                bufbackpages = 100;

        /*
         * If the MD code does not say otherwise, reserve 10% of kva
         * space for mapping buffers.
         */
        if (bufkvm == 0)
                bufkvm = VM_KERNEL_SPACE_SIZE / 10;

        /*
         * Don't use more than twice the amount of bufpages for mappings.
         * It's twice since we map things sparsely.
         */
        if (bufkvm > bufpages * PAGE_SIZE)
                bufkvm = bufpages * PAGE_SIZE;
        /*
         * Round bufkvm to MAXPHYS because we allocate chunks of va space
         * in MAXPHYS chunks.
         */
        bufkvm &= ~(MAXPHYS - 1);

        pool_init(&bufpool, sizeof(struct buf), 0, IPL_BIO, 0, "bufpl", NULL);

        bufcache_init();

        /*
         * hmm - bufkvm is an argument because it's static, while
         * bufpages is global because it can change while running.
         */
        buf_mem_init(bufkvm);

        /*
         * Set the dirty page high water mark to be less than the low
         * water mark for pages in the buffer cache. This ensures we
         * can always back off by throwing away clean pages, and give
         * ourselves a chance to write out the dirty pages eventually.
         */
        hidirtypages = (buflowpages / 4) * 3;
        lodirtypages = buflowpages / 2;

        /*
         * We are allowed to use up to the reserve.
         */
        targetpages = bufpages - RESERVE_PAGES;
}

/*
 * Change cachepct
 */
void
bufadjust(int newbufpages)
{
        int s;
        int64_t npages;

        if (newbufpages < buflowpages)
                newbufpages = buflowpages;

        s = splbio();
        bufpages = newbufpages;

        /*
         * We are allowed to use up to the reserve
         */
        targetpages = bufpages - RESERVE_PAGES;

        npages = bcstats.dmapages - targetpages;

        /*
         * Shrinking the cache happens here only if someone has manually
         * adjusted bufcachepercent - or the pagedaemon has told us
         * to give back memory *now* - so we give it all back.
         */
        if (bcstats.dmapages > targetpages)
                (void) bufcache_recover_dmapages(0, bcstats.dmapages - targetpages);
        bufcache_adjust();

        /*
         * Wake up the cleaner if we have lots of dirty pages,
         * or if we are getting low on buffer cache kva.
         */
        if ((UNCLEAN_PAGES >= hidirtypages) ||
            bcstats.kvaslots_avail <= 2 * RESERVE_SLOTS)
                wakeup(&bd_req);

        splx(s);
}

/*
 * Back off "size" buffer cache pages. Called by the page
 * daemon to consume buffer cache pages rather than scanning.
 *
 * It returns the number of freed pages.
 */
unsigned long
bufbackoff(struct uvm_constraint_range *range, long size)
{
        long pdelta, oldbufpages;
        int64_t dmarecovered, recovered = 0;

        /*
         * If we will accept high memory for this backoff
         * try to steal it from the high memory buffer cache.
         */
        if (range != NULL && range->ucr_high > dma_constraint.ucr_high) {
                struct buf *bp;
                int64_t start;
                int s;

                start = bcstats.numbufpages;

                s = splbio();
                while (recovered < size && (bp = bufcache_gethighcleanbuf())) {
                        bufcache_take(bp);
                        if (bp->b_vp) {
                                RBT_REMOVE(buf_rb_bufs,
                                    &bp->b_vp->v_bufs_tree, bp);
                                brelvp(bp);
                        }
                        buf_put(bp);
                        recovered = start - bcstats.numbufpages;
                }
                bufcache_adjust();
                splx(s);

                /* We got enough. */
                if (recovered >= size)
                        return recovered;

                /* If we needed only memory above DMA, we're done. */
                if (range->ucr_low > dma_constraint.ucr_high)
                        return recovered;

                /* Otherwise get the rest from DMA */
                size -= recovered;
        }

        /*
         * XXX Otherwise do the dma memory cache dance. this needs
         * refactoring later to get rid of 'bufpages'
         */

        /*
         * Back off by at least bufbackpages. If the page daemon gave us
         * a larger size, back off by that much.
         */
        pdelta = (size > bufbackpages) ? size : bufbackpages;

        if (bufpages <= buflowpages)
                return recovered;
        if (bufpages - pdelta < buflowpages)
                pdelta = bufpages - buflowpages;
        oldbufpages = bufpages;
        bufadjust(bufpages - pdelta);
        dmarecovered = oldbufpages - bufpages;

        return recovered + dmarecovered;
}


/*
 * Opportunistically flip a buffer into high memory. Will move the buffer
 * if memory is available without sleeping, and return 0, otherwise will
 * fail and return -1 with the buffer unchanged.
 */

int
buf_flip_high(struct buf *bp)
{
        int ret = -1;

        KASSERT(ISSET(bp->b_flags, B_BC));
        KASSERT(ISSET(bp->b_flags, B_DMA));
        KASSERT(bp->cache == DMA_CACHE);
        KASSERT(fliphigh);

        splassert(IPL_BIO);

        /* Attempt to move the buffer to high memory if we can */
        if (buf_realloc_pages(bp, &high_constraint, UVM_PLA_NOWAIT) == 0) {
                KASSERT(!ISSET(bp->b_flags, B_DMA));
                bcstats.highflips++;
                ret = 0;
        } else
                bcstats.highflops++;

        return ret;
}

/*
 * Flip a buffer to dma reachable memory, when we need it there for
 * I/O. This can sleep since it will wait for memory allocation in the
 * DMA reachable area since we have to have the buffer there to proceed.
 */
void
buf_flip_dma(struct buf *bp)
{
        KASSERT(ISSET(bp->b_flags, B_BC));
        KASSERT(ISSET(bp->b_flags, B_BUSY));
        KASSERT(bp->cache < NUM_CACHES);

        splassert(IPL_BIO);

        if (!ISSET(bp->b_flags, B_DMA)) {

                /* move buf to dma reachable memory */
                (void) buf_realloc_pages(bp, &dma_constraint, UVM_PLA_WAITOK);
                KASSERT(ISSET(bp->b_flags, B_DMA));
                bcstats.dmaflips++;
        }

        if (bp->cache > DMA_CACHE) {
                CLR(bp->b_flags, B_COLD);
                CLR(bp->b_flags, B_WARM);
                bp->cache = DMA_CACHE;
        }
}

struct buf *
bio_doread(struct vnode *vp, daddr_t blkno, int size, int async)
{
        struct buf *bp;
        struct mount *mp;

        bp = getblk(vp, blkno, size, 0, INFSLP);

        /*
         * If buffer does not have valid data, start a read.
         * Note that if buffer is B_INVAL, getblk() won't return it.
         * Therefore, it's valid if its I/O has completed or been delayed.
         */
        if (!ISSET(bp->b_flags, (B_DONE | B_DELWRI))) {
                SET(bp->b_flags, B_READ | async);
                bcstats.pendingreads++;
                bcstats.numreads++;
                VOP_STRATEGY(bp->b_vp, bp);
                /* Pay for the read. */
                curproc->p_ru.ru_inblock++;                     /* XXX */
        } else if (async) {
                brelse(bp);
        }

        mp = vp->v_type == VBLK ? vp->v_specmountpoint : vp->v_mount;

        /*
         * Collect statistics on synchronous and asynchronous reads.
         * Reads from block devices are charged to their associated
         * filesystem (if any).
         */
        if (mp != NULL) {
                if (async == 0)
                        mp->mnt_stat.f_syncreads++;
                else
                        mp->mnt_stat.f_asyncreads++;
        }

        return (bp);
}

/*
 * Read a disk block.
 * This algorithm described in Bach (p.54).
 */
int
bread(struct vnode *vp, daddr_t blkno, int size, struct buf **bpp)
{
        struct buf *bp;

        /* Get buffer for block. */
        bp = *bpp = bio_doread(vp, blkno, size, 0);

        /* Wait for the read to complete, and return result. */
        return (biowait(bp));
}

/*
 * Read-ahead multiple disk blocks. The first is sync, the rest async.
 * Trivial modification to the breada algorithm presented in Bach (p.55).
 */
int
breadn(struct vnode *vp, daddr_t blkno, int size, daddr_t rablks[],
    int rasizes[], int nrablks, struct buf **bpp)
{
        struct buf *bp;
        int i;

        bp = *bpp = bio_doread(vp, blkno, size, 0);

        /*
         * For each of the read-ahead blocks, start a read, if necessary.
         */
        for (i = 0; i < nrablks; i++) {
                /* If it's in the cache, just go on to next one. */
                if (incore(vp, rablks[i]))
                        continue;

                /* Get a buffer for the read-ahead block */
                (void) bio_doread(vp, rablks[i], rasizes[i], B_ASYNC);
        }

        /* Otherwise, we had to start a read for it; wait until it's valid. */
        return (biowait(bp));
}

/*
 * Called from interrupt context.
 */
void
bread_cluster_callback(struct buf *bp)
{
        struct buf **xbpp = bp->b_saveaddr;
        int i;

        if (xbpp[1] != NULL) {
                size_t newsize = xbpp[1]->b_bufsize;

                /*
                 * Shrink this buffer's mapping to only cover its part of
                 * the total I/O.
                 */
                buf_fix_mapping(bp, newsize);
                bp->b_bcount = newsize;
        }

        /* Invalidate read-ahead buffers if read short */
        if (bp->b_resid > 0) {
                for (i = 1; xbpp[i] != NULL; i++)
                        continue;
                for (i = i - 1; i != 0; i--) {
                        if (xbpp[i]->b_bufsize <= bp->b_resid) {
                                bp->b_resid -= xbpp[i]->b_bufsize;
                                SET(xbpp[i]->b_flags, B_INVAL);
                        } else if (bp->b_resid > 0) {
                                bp->b_resid = 0;
                                SET(xbpp[i]->b_flags, B_INVAL);
                        } else
                                break;
                }
        }

        for (i = 1; xbpp[i] != NULL; i++) {
                if (ISSET(bp->b_flags, B_ERROR))
                        SET(xbpp[i]->b_flags, B_INVAL | B_ERROR);
                /*
                 * Move the pages from the master buffer's uvm object
                 * into the individual buffer's uvm objects.
                 */
                struct uvm_object *newobj = &xbpp[i]->b_uobj;
                struct uvm_object *oldobj = &bp->b_uobj;
                int page;

                uvm_obj_init(newobj, &bufcache_pager, 1);
                for (page = 0; page < atop(xbpp[i]->b_bufsize); page++) {
                        struct vm_page *pg = uvm_pagelookup(oldobj,
                            xbpp[i]->b_poffs + ptoa(page));
                        KASSERT(pg != NULL);
                        KASSERT(pg->wire_count == 1);
                        uvm_pagerealloc(pg, newobj, xbpp[i]->b_poffs + ptoa(page));
                }
                xbpp[i]->b_pobj = newobj;

                biodone(xbpp[i]);
        }

        free(xbpp, M_TEMP, (i + 1) * sizeof(*xbpp));

        if (ISSET(bp->b_flags, B_ASYNC)) {
                brelse(bp);
        } else {
                CLR(bp->b_flags, B_WANTED);
                wakeup(bp);
        }
}

/*
 * Read-ahead multiple disk blocks, but make sure only one (big) I/O
 * request is sent to the disk.
 * XXX This should probably be dropped and breadn should instead be optimized
 * XXX to do fewer I/O requests.
 */
int
bread_cluster(struct vnode *vp, daddr_t blkno, int size, struct buf **rbpp)
{
        struct buf *bp, **xbpp;
        int howmany, maxra, i, inc;
        daddr_t sblkno;

        *rbpp = bio_doread(vp, blkno, size, 0);

        /*
         * If the buffer is in the cache skip any I/O operation.
         */
        if (ISSET((*rbpp)->b_flags, B_CACHE))
                goto out;

        if (size != round_page(size))
                goto out;

        if (VOP_BMAP(vp, blkno + 1, NULL, &sblkno, &maxra))
                goto out;

        maxra++;
        if (sblkno == -1 || maxra < 2)
                goto out;

        howmany = MAXPHYS / size;
        if (howmany > maxra)
                howmany = maxra;

        xbpp = mallocarray(howmany + 1, sizeof(*xbpp), M_TEMP, M_NOWAIT);
        if (xbpp == NULL)
                goto out;

        for (i = howmany - 1; i >= 0; i--) {
                size_t sz;

                /*
                 * First buffer allocates big enough size to cover what
                 * all the other buffers need.
                 */
                sz = i == 0 ? howmany * size : 0;

                xbpp[i] = buf_get(vp, blkno + i + 1, sz);
                if (xbpp[i] == NULL) {
                        for (++i; i < howmany; i++) {
                                SET(xbpp[i]->b_flags, B_INVAL);
                                brelse(xbpp[i]);
                        }
                        free(xbpp, M_TEMP, (howmany + 1) * sizeof(*xbpp));
                        goto out;
                }
        }

        bp = xbpp[0];

        xbpp[howmany] = NULL;

        inc = btodb(size);

        for (i = 1; i < howmany; i++) {
                bcstats.pendingreads++;
                bcstats.numreads++;
                /*
                * We set B_DMA here because bp above will be B_DMA,
                * and we are playing buffer slice-n-dice games from
                * the memory allocated in bp.
                */
                SET(xbpp[i]->b_flags, B_DMA | B_READ | B_ASYNC);
                xbpp[i]->b_blkno = sblkno + (i * inc);
                xbpp[i]->b_bufsize = xbpp[i]->b_bcount = size;
                xbpp[i]->b_data = NULL;
                xbpp[i]->b_pobj = bp->b_pobj;
                xbpp[i]->b_poffs = bp->b_poffs + (i * size);
        }

        KASSERT(bp->b_lblkno == blkno + 1);
        KASSERT(bp->b_vp == vp);

        bp->b_blkno = sblkno;
        SET(bp->b_flags, B_READ | B_ASYNC | B_CALL);

        bp->b_saveaddr = (void *)xbpp;
        bp->b_iodone = bread_cluster_callback;

        bcstats.pendingreads++;
        bcstats.numreads++;
        VOP_STRATEGY(bp->b_vp, bp);
        curproc->p_ru.ru_inblock++;

out:
        return (biowait(*rbpp));
}

/*
 * Block write.  Described in Bach (p.56)
 */
int
bwrite(struct buf *bp)
{
        int rv, async, wasdelayed, s;
        struct vnode *vp;
        struct mount *mp;

        vp = bp->b_vp;
        if (vp != NULL)
                mp = vp->v_type == VBLK? vp->v_specmountpoint : vp->v_mount;
        else
                mp = NULL;

        /*
         * Remember buffer type, to switch on it later.  If the write was
         * synchronous, but the file system was mounted with MNT_ASYNC,
         * convert it to a delayed write.
         * XXX note that this relies on delayed tape writes being converted
         * to async, not sync writes (which is safe, but ugly).
         */
        async = ISSET(bp->b_flags, B_ASYNC);
        if (!async && mp && ISSET(mp->mnt_flag, MNT_ASYNC)) {
                /*
                 * Don't convert writes from VND on async filesystems
                 * that already have delayed writes in the upper layer.
                 */
                if (!ISSET(bp->b_flags, B_NOCACHE)) {
                        bdwrite(bp);
                        return (0);
                }
        }

        /*
         * Collect statistics on synchronous and asynchronous writes.
         * Writes to block devices are charged to their associated
         * filesystem (if any).
         */
        if (mp != NULL) {
                if (async)
                        mp->mnt_stat.f_asyncwrites++;
                else
                        mp->mnt_stat.f_syncwrites++;
        }
        bcstats.pendingwrites++;
        bcstats.numwrites++;

        wasdelayed = ISSET(bp->b_flags, B_DELWRI);
        CLR(bp->b_flags, (B_READ | B_DONE | B_ERROR | B_DELWRI));

        s = splbio();

        /*
         * If not synchronous, pay for the I/O operation and make
         * sure the buf is on the correct vnode queue.  We have
         * to do this now, because if we don't, the vnode may not
         * be properly notified that its I/O has completed.
         */
        if (wasdelayed) {
                reassignbuf(bp);
        } else
                curproc->p_ru.ru_oublock++;


        /* Initiate disk write.  Make sure the appropriate party is charged. */
        bp->b_vp->v_numoutput++;
        buf_flip_dma(bp);
        SET(bp->b_flags, B_WRITEINPROG);
        splx(s);
        VOP_STRATEGY(bp->b_vp, bp);

        /*
         * If the queue is above the high water mark, wait till
         * the number of outstanding write bufs drops below the low
         * water mark.
         */
        if (bp->b_bq)
                bufq_wait(bp->b_bq);

        if (async)
                return (0);

        /*
         * If I/O was synchronous, wait for it to complete.
         */
        rv = biowait(bp);

        /* Release the buffer. */
        brelse(bp);

        return (rv);
}


/*
 * Delayed write.
 *
 * The buffer is marked dirty, but is not queued for I/O.
 * This routine should be used when the buffer is expected
 * to be modified again soon, typically a small write that
 * partially fills a buffer.
 *
 * NB: magnetic tapes cannot be delayed; they must be
 * written in the order that the writes are requested.
 *
 * Described in Leffler, et al. (pp. 208-213).
 */
void
bdwrite(struct buf *bp)
{
        int s;

        /*
         * If the block hasn't been seen before:
         *      (1) Mark it as having been seen,
         *      (2) Charge for the write.
         *      (3) Make sure it's on its vnode's correct block list,
         *      (4) If a buffer is rewritten, move it to end of dirty list
         */
        if (!ISSET(bp->b_flags, B_DELWRI)) {
                SET(bp->b_flags, B_DELWRI);
                s = splbio();
                buf_flip_dma(bp);
                reassignbuf(bp);
                splx(s);
                curproc->p_ru.ru_oublock++;             /* XXX */
        }

        /* The "write" is done, so mark and release the buffer. */
        CLR(bp->b_flags, B_NEEDCOMMIT);
        CLR(bp->b_flags, B_NOCACHE); /* Must cache delayed writes */
        SET(bp->b_flags, B_DONE);
        brelse(bp);
}

/*
 * Asynchronous block write; just an asynchronous bwrite().
 */
void
bawrite(struct buf *bp)
{

        SET(bp->b_flags, B_ASYNC);
        VOP_BWRITE(bp);
}

/*
 * Must be called at splbio()
 */
void
buf_dirty(struct buf *bp)
{
        splassert(IPL_BIO);

#ifdef DIAGNOSTIC
        if (!ISSET(bp->b_flags, B_BUSY))
                panic("Trying to dirty buffer on freelist!");
#endif

        if (ISSET(bp->b_flags, B_DELWRI) == 0) {
                SET(bp->b_flags, B_DELWRI);
                buf_flip_dma(bp);
                reassignbuf(bp);
        }
}

/*
 * Must be called at splbio()
 */
void
buf_undirty(struct buf *bp)
{
        splassert(IPL_BIO);

#ifdef DIAGNOSTIC
        if (!ISSET(bp->b_flags, B_BUSY))
                panic("Trying to undirty buffer on freelist!");
#endif
        if (ISSET(bp->b_flags, B_DELWRI)) {
                CLR(bp->b_flags, B_DELWRI);
                reassignbuf(bp);
        }
}

/*
 * Release a buffer on to the free lists.
 * Described in Bach (p. 46).
 */
void
brelse(struct buf *bp)
{
        int s;

        s = splbio();

        if (bp->b_data != NULL)
                KASSERT(bp->b_bufsize > 0);

        /*
         * Determine which queue the buffer should be on, then put it there.
         */

        /* If it's not cacheable, or an error, mark it invalid. */
        if (ISSET(bp->b_flags, (B_NOCACHE|B_ERROR)))
                SET(bp->b_flags, B_INVAL);
        /* If it's a write error, also mark the vnode as damaged. */
        if (ISSET(bp->b_flags, B_ERROR) && !ISSET(bp->b_flags, B_READ)) {
                if (bp->b_vp && bp->b_vp->v_type == VREG)
                        SET(bp->b_vp->v_bioflag, VBIOERROR);
        }

        if (ISSET(bp->b_flags, B_INVAL)) {
                /*
                 * If the buffer is invalid, free it now rather than leaving
                 * it in a queue and wasting memory.
                 */
                if (ISSET(bp->b_flags, B_DELWRI)) {
                        CLR(bp->b_flags, B_DELWRI);
                }

                if (bp->b_vp) {
                        RBT_REMOVE(buf_rb_bufs, &bp->b_vp->v_bufs_tree, bp);
                        brelvp(bp);
                }
                bp->b_vp = NULL;

                /*
                 * Wake up any processes waiting for _this_ buffer to
                 * become free. They are not allowed to grab it
                 * since it will be freed. But the only sleeper is
                 * getblk and it will restart the operation after
                 * sleep.
                 */
                if (ISSET(bp->b_flags, B_WANTED)) {
                        CLR(bp->b_flags, B_WANTED);
                        wakeup(bp);
                }
                buf_put(bp);
        } else {
                /*
                 * It has valid data.  Put it on the end of the appropriate
                 * queue, so that it'll stick around for as long as possible.
                 */
                bufcache_release(bp);

                /* Unlock the buffer. */
                CLR(bp->b_flags, (B_AGE | B_ASYNC | B_NOCACHE | B_DEFERRED));
                buf_release(bp);

                /* Wake up any processes waiting for _this_ buffer to
                 * become free. */
                if (ISSET(bp->b_flags, B_WANTED)) {
                        CLR(bp->b_flags, B_WANTED);
                        wakeup(bp);
                }

                if (bcstats.dmapages > targetpages)
                        (void) bufcache_recover_dmapages(0,
                            bcstats.dmapages - targetpages);
                bufcache_adjust();
        }

        /* Wake up syncer and cleaner processes waiting for buffers. */
        if (nobuffers) {
                nobuffers = 0;
                wakeup(&nobuffers);
        }

        /* Wake up any processes waiting for any buffer to become free. */
        if (needbuffer && bcstats.dmapages < targetpages &&
            bcstats.kvaslots_avail > RESERVE_SLOTS) {
                needbuffer = 0;
                wakeup(&needbuffer);
        }

        splx(s);
}

/*
 * Determine if a block is in the cache. Just look on what would be its hash
 * chain. If it's there, return a pointer to it, unless it's marked invalid.
 */
static struct buf *
incore_locked(struct vnode *vp, daddr_t blkno)
{
        struct buf *bp;
        struct buf b;

        splassert(IPL_BIO);

        /* Search buf lookup tree */
        b.b_lblkno = blkno;
        bp = RBT_FIND(buf_rb_bufs, &vp->v_bufs_tree, &b);
        if (bp != NULL && ISSET(bp->b_flags, B_INVAL))
                bp = NULL;

        return (bp);
}
struct buf *
incore(struct vnode *vp, daddr_t blkno)
{
        struct buf *bp;
        int s;

        s = splbio();
        bp = incore_locked(vp, blkno);
        splx(s);

        return (bp);
}

/*
 * Get a block of requested size that is associated with
 * a given vnode and block offset. If it is found in the
 * block cache, mark it as having been found, make it busy
 * and return it. Otherwise, return an empty block of the
 * correct size. It is up to the caller to ensure that the
 * cached blocks be of the correct size.
 */
struct buf *
getblk(struct vnode *vp, daddr_t blkno, int size, int slpflag,
    uint64_t slptimeo)
{
        struct buf *bp;
        struct buf b;
        int s, error;

        /*
         * XXX
         * The following is an inlined version of 'incore()', but with
         * the 'invalid' test moved to after the 'busy' test.  It's
         * necessary because there are some cases in which the NFS
         * code sets B_INVAL prior to writing data to the server, but
         * in which the buffers actually contain valid data.  In this
         * case, we can't allow the system to allocate a new buffer for
         * the block until the write is finished.
         */
start:
        s = splbio();
        b.b_lblkno = blkno;
        bp = RBT_FIND(buf_rb_bufs, &vp->v_bufs_tree, &b);
        if (bp != NULL) {
                if (ISSET(bp->b_flags, B_BUSY)) {
                        SET(bp->b_flags, B_WANTED);
                        error = tsleep_nsec(bp, slpflag | (PRIBIO + 1),
                            "getblk", slptimeo);
                        splx(s);
                        if (error)
                                return (NULL);
                        goto start;
                }

                if (!ISSET(bp->b_flags, B_INVAL)) {
                        bcstats.cachehits++;
                        SET(bp->b_flags, B_CACHE);
                        bufcache_take(bp);
                        buf_acquire(bp);
                        splx(s);
                        return (bp);
                }
        }
        splx(s);

        if ((bp = buf_get(vp, blkno, size)) == NULL)
                goto start;

        return (bp);
}

/*
 * Get an empty, disassociated buffer of given size.
 */
struct buf *
geteblk(size_t size)
{
        struct buf *bp;

        while ((bp = buf_get(NULL, 0, size)) == NULL)
                continue;

        return (bp);
}

/*
 * Allocate a buffer.
 * If vp is given, put it into the buffer cache for that vnode.
 * If size != 0, allocate memory and call buf_map().
 * If there is already a buffer for the given vnode/blkno, return NULL.
 */
struct buf *
buf_get(struct vnode *vp, daddr_t blkno, size_t size)
{
        struct buf *bp;
        int poolwait = size == 0 ? PR_NOWAIT : PR_WAITOK;
        int npages;
        int s;

        s = splbio();
        if (size) {
                /*
                 * Wake up the cleaner if we have lots of dirty pages,
                 * or if we are getting low on buffer cache kva.
                 */
                if (UNCLEAN_PAGES >= hidirtypages ||
                        bcstats.kvaslots_avail <= 2 * RESERVE_SLOTS)
                        wakeup(&bd_req);

                npages = atop(round_page(size));

                /*
                 * if our cache has been previously shrunk,
                 * allow it to grow again with use up to
                 * bufhighpages (cachepercent)
                 */
                if (bufpages < bufhighpages)
                        bufadjust(bufhighpages);

                /*
                 * If we would go over the page target with our
                 * new allocation, free enough buffers first
                 * to stay at the target with our new allocation.
                 */
                if (bcstats.dmapages + npages > targetpages) {
                        (void) bufcache_recover_dmapages(0, npages);
                        bufcache_adjust();
                }

                /*
                 * If we get here, we tried to free the world down
                 * above, and couldn't get down - Wake the cleaner
                 * and wait for it to push some buffers out.
                 */
                if ((bcstats.dmapages + npages > targetpages ||
                    bcstats.kvaslots_avail <= RESERVE_SLOTS) &&
                    curproc != syncerproc && curproc != cleanerproc) {
                        wakeup(&bd_req);
                        needbuffer++;
                        tsleep_nsec(&needbuffer, PRIBIO, "needbuffer", INFSLP);
                        splx(s);
                        return (NULL);
                }
                if (bcstats.dmapages + npages > bufpages) {
                        /* cleaner or syncer */
                        nobuffers = 1;
                        tsleep_nsec(&nobuffers, PRIBIO, "nobuffers", INFSLP);
                        splx(s);
                        return (NULL);
                }
        }

        bp = pool_get(&bufpool, poolwait|PR_ZERO);

        if (bp == NULL) {
                splx(s);
                return (NULL);
        }

        bp->b_freelist.tqe_next = NOLIST;
        bp->b_dev = NODEV;
        bp->b_bcount = size;

        buf_acquire_nomap(bp);

        if (vp != NULL) {
                /*
                 * We insert the buffer into the hash with B_BUSY set
                 * while we allocate pages for it. This way any getblk
                 * that happens while we allocate pages will wait for
                 * this buffer instead of starting its own buf_get.
                 *
                 * But first, we check if someone beat us to it.
                 */
                if (incore_locked(vp, blkno)) {
                        pool_put(&bufpool, bp);
                        splx(s);
                        return (NULL);
                }

                bp->b_blkno = bp->b_lblkno = blkno;
                bgetvp(vp, bp);
                if (RBT_INSERT(buf_rb_bufs, &vp->v_bufs_tree, bp))
                        panic("buf_get: dup lblk vp %p bp %p", vp, bp);
        } else {
                bp->b_vnbufs.le_next = NOLIST;
                SET(bp->b_flags, B_INVAL);
                bp->b_vp = NULL;
        }

        LIST_INSERT_HEAD(&bufhead, bp, b_list);
        bcstats.numbufs++;

        if (size) {
                buf_alloc_pages(bp, round_page(size));
                KASSERT(ISSET(bp->b_flags, B_DMA));
                buf_map(bp);
        }

        SET(bp->b_flags, B_BC);
        splx(s);

        return (bp);
}

/*
 * Buffer cleaning daemon.
 */
void
buf_daemon(void *arg)
{
        struct buf *bp = NULL;
        int s, pushed = 0;

        s = splbio();
        for (;;) {
                if (bp == NULL || (pushed >= 16 &&
                    UNCLEAN_PAGES < hidirtypages &&
                    bcstats.kvaslots_avail > 2 * RESERVE_SLOTS)){
                        pushed = 0;
                        /*
                         * Wake up anyone who was waiting for buffers
                         * to be released.
                         */
                        if (needbuffer) {
                                needbuffer = 0;
                                wakeup(&needbuffer);
                        }
                        tsleep_nsec(&bd_req, PRIBIO - 7, "cleaner", INFSLP);
                }

                while ((bp = bufcache_getdirtybuf())) {
                        TRACEPOINT(vfs, cleaner, bp->b_flags, pushed,
                            lodirtypages, hidirtypages);

                        if (UNCLEAN_PAGES < lodirtypages &&
                            bcstats.kvaslots_avail > 2 * RESERVE_SLOTS &&
                            pushed >= 16)
                                break;

                        bufcache_take(bp);
                        buf_acquire(bp);
                        splx(s);

                        if (ISSET(bp->b_flags, B_INVAL)) {
                                brelse(bp);
                                s = splbio();
                                continue;
                        }
#ifdef DIAGNOSTIC
                        if (!ISSET(bp->b_flags, B_DELWRI))
                                panic("Clean buffer on dirty queue");
#endif
                        bawrite(bp);
                        pushed++;

                        sched_pause(yield);

                        s = splbio();
                }
        }
}

/*
 * Wait for operations on the buffer to complete.
 * When they do, extract and return the I/O's error value.
 */
int
biowait(struct buf *bp)
{
        int s;

        KASSERT(!(bp->b_flags & B_ASYNC));

        s = splbio();
        while (!ISSET(bp->b_flags, B_DONE))
                tsleep_nsec(bp, PRIBIO + 1, "biowait", INFSLP);
        splx(s);

        /* check for interruption of I/O (e.g. via NFS), then errors. */
        if (ISSET(bp->b_flags, B_EINTR)) {
                CLR(bp->b_flags, B_EINTR);
                return (EINTR);
        }

        if (ISSET(bp->b_flags, B_ERROR))
                return (bp->b_error ? bp->b_error : EIO);
        else
                return (0);
}

/*
 * Mark I/O complete on a buffer.
 *
 * If a callback has been requested, e.g. the pageout
 * daemon, do so. Otherwise, awaken waiting processes.
 *
 * [ Leffler, et al., says on p.247:
 *      "This routine wakes up the blocked process, frees the buffer
 *      for an asynchronous write, or, for a request by the pagedaemon
 *      process, invokes a procedure specified in the buffer structure" ]
 *
 * In real life, the pagedaemon (or other system processes) wants
 * to do async stuff to, and doesn't want the buffer brelse()'d.
 * (for swap pager, that puts swap buffers on the free lists (!!!),
 * for the vn device, that puts malloc'd buffers on the free lists!)
 *
 * Must be called at splbio().
 */
void
biodone(struct buf *bp)
{
        splassert(IPL_BIO);

        if (ISSET(bp->b_flags, B_DONE))
                panic("biodone already");
        SET(bp->b_flags, B_DONE);               /* note that it's done */

        if (bp->b_bq)
                bufq_done(bp->b_bq, bp);

        if (!ISSET(bp->b_flags, B_READ)) {
                CLR(bp->b_flags, B_WRITEINPROG);
                vwakeup(bp->b_vp);
        }
        if (bcstats.numbufs &&
            (!(ISSET(bp->b_flags, B_RAW) || ISSET(bp->b_flags, B_PHYS)))) {
                if (!ISSET(bp->b_flags, B_READ)) {
                        bcstats.pendingwrites--;
                } else
                        bcstats.pendingreads--;
        }
        if (ISSET(bp->b_flags, B_CALL)) {       /* if necessary, call out */
                CLR(bp->b_flags, B_CALL);       /* but note callout done */
                (*bp->b_iodone)(bp);
        } else {
                if (ISSET(bp->b_flags, B_ASYNC)) {/* if async, release it */
                        brelse(bp);
                } else {                        /* or just wakeup the buffer */
                        CLR(bp->b_flags, B_WANTED);
                        wakeup(bp);
                }
        }
}

#ifdef DDB
void    bcstats_print(int (*)(const char *, ...)
    __attribute__((__format__(__kprintf__,1,2))));
/*
 * bcstats_print: ddb hook to print interesting buffer cache counters
 */
void
bcstats_print(
    int (*pr)(const char *, ...) __attribute__((__format__(__kprintf__,1,2))))
{
        (*pr)("Current Buffer Cache status:\n");
        (*pr)("numbufs %lld busymapped %lld, delwri %lld\n",
            bcstats.numbufs, bcstats.busymapped, bcstats.delwribufs);
        (*pr)("kvaslots %lld avail kva slots %lld\n",
            bcstats.kvaslots, bcstats.kvaslots_avail);
        (*pr)("bufpages %lld, dmapages %lld, dirtypages %lld\n",
            bcstats.numbufpages, bcstats.dmapages, bcstats.numdirtypages);
        (*pr)("pendingreads %lld, pendingwrites %lld\n",
            bcstats.pendingreads, bcstats.pendingwrites);
        (*pr)("highflips %lld, highflops %lld, dmaflips %lld\n",
            bcstats.highflips, bcstats.highflops, bcstats.dmaflips);
}
#endif

void
buf_adjcnt(struct buf *bp, long ncount)
{
        KASSERT(ncount <= bp->b_bufsize);
        bp->b_bcount = ncount;
}

/* bufcache freelist code below */
/*
 * Copyright (c) 2014 Ted Unangst <tedu@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

/*
 * The code below implements a variant of the 2Q buffer cache algorithm by
 * Johnson and Shasha.
 *
 * General Outline
 * We divide the buffer cache into three working sets: current, previous,
 * and long term. Each list is itself LRU and buffers get promoted and moved
 * around between them. A buffer starts its life in the current working set.
 * As time passes and newer buffers push it out, it will turn into the previous
 * working set and is subject to recycling. But if it's accessed again from
 * the previous working set, that's an indication that it's actually in the
 * long term working set, so we promote it there. The separation of current
 * and previous working sets prevents us from promoting a buffer that's only
 * temporarily hot to the long term cache.
 *
 * The objective is to provide scan resistance by making the long term
 * working set ineligible for immediate recycling, even as the current
 * working set is rapidly turned over.
 *
 * Implementation
 * The code below identifies the current, previous, and long term sets as
 * hotqueue, coldqueue, and warmqueue. The hot and warm queues are capped at
 * 1/3 of the total clean pages, after which point they start pushing their
 * oldest buffers into coldqueue.
 * A buf always starts out with neither WARM or COLD flags set (implying HOT).
 * When released, it will be returned to the tail of the hotqueue list.
 * When the hotqueue gets too large, the oldest hot buf will be moved to the
 * coldqueue, with the B_COLD flag set. When a cold buf is released, we set
 * the B_WARM flag and put it onto the warmqueue. Warm bufs are also
 * directly returned to the end of the warmqueue. As with the hotqueue, when
 * the warmqueue grows too large, B_WARM bufs are moved onto the coldqueue.
 *
 * Note that this design does still support large working sets, greater
 * than the cap of hotqueue or warmqueue would imply. The coldqueue is still
 * cached and has no maximum length. The hot and warm queues form a Y feeding
 * into the coldqueue. Moving bufs between queues is constant time, so this
 * design decays to one long warm->cold queue.
 *
 * In the 2Q paper, hotqueue and coldqueue are A1in and A1out. The warmqueue
 * is Am. We always cache pages, as opposed to pointers to pages for A1.
 *
 * This implementation adds support for multiple 2q caches.
 *
 * If we have more than one 2q cache, as bufs fall off the cold queue
 * for recycling, bufs that have been warm before (which retain the
 * B_WARM flag in addition to B_COLD) can be put into the hot queue of
 * a second level 2Q cache. buffers which are only B_COLD are
 * recycled. Bufs falling off the last cache's cold queue are always
 * recycled.
 *
 */

/*
 * this function is called when a hot or warm queue may have exceeded its
 * size limit. it will move a buf to the coldqueue.
 */
int chillbufs(struct
    bufcache *cache, struct bufqueue *queue, int64_t *queuepages);

void
bufcache_init(void)
{
        int i;

        for (i = 0; i < NUM_CACHES; i++) {
                TAILQ_INIT(&cleancache[i].hotqueue);
                TAILQ_INIT(&cleancache[i].coldqueue);
                TAILQ_INIT(&cleancache[i].warmqueue);
        }
        TAILQ_INIT(&dirtyqueue);
}

/*
 * if the buffer caches have shrunk, we may need to rebalance our queues.
 */
void
bufcache_adjust(void)
{
        int i;

        for (i = 0; i < NUM_CACHES; i++) {
                while (chillbufs(&cleancache[i], &cleancache[i].warmqueue,
                    &cleancache[i].warmbufpages) ||
                    chillbufs(&cleancache[i], &cleancache[i].hotqueue,
                    &cleancache[i].hotbufpages))
                        continue;
        }
}

/*
 * Get a clean buffer from the cache. if "discard" is set do not promote
 * previously warm buffers as normal, because we are tossing everything
 * away such as in a hibernation
 */
struct buf *
bufcache_getcleanbuf(int cachenum, int discard)
{
        struct buf *bp = NULL;
        struct bufcache *cache = &cleancache[cachenum];
        struct bufqueue * queue;

        splassert(IPL_BIO);

        /* try cold queue */
        while ((bp = TAILQ_FIRST(&cache->coldqueue)) ||
            (bp = TAILQ_FIRST(&cache->warmqueue)) ||
            (bp = TAILQ_FIRST(&cache->hotqueue))) {
                int64_t pages = atop(bp->b_bufsize);
                struct bufcache *newcache;

                if (discard || cachenum >= NUM_CACHES - 1) {
                        /* Victim selected, give it up */
                        return bp;
                }
                KASSERT(bp->cache == cachenum);

                /*
                 * If this buffer was warm before, move it to
                 * the hot queue in the next cache
                 */

                if (fliphigh) {
                        /*
                         * If we are in the DMA cache, try to flip the
                         * buffer up high to move it on to the other
                         * caches. if we can't move the buffer to high
                         * memory without sleeping, we give it up and
                         * return it rather than fight for more memory
                         * against non buffer cache competitors.
                         */
                        SET(bp->b_flags, B_BUSY);
                        if (bp->cache == 0 && buf_flip_high(bp) == -1) {
                                CLR(bp->b_flags, B_BUSY);
                                return bp;
                        }
                        CLR(bp->b_flags, B_BUSY);
                }

                /* Move the buffer to the hot queue in the next cache */
                if (ISSET(bp->b_flags, B_COLD)) {
                        queue = &cache->coldqueue;
                } else if (ISSET(bp->b_flags, B_WARM)) {
                        queue = &cache->warmqueue;
                        cache->warmbufpages -= pages;
                } else {
                        queue = &cache->hotqueue;
                        cache->hotbufpages -= pages;
                }
                TAILQ_REMOVE(queue, bp, b_freelist);
                cache->cachepages -= pages;
                CLR(bp->b_flags, B_WARM);
                CLR(bp->b_flags, B_COLD);
                bp->cache++;
                newcache= &cleancache[bp->cache];
                newcache->cachepages += pages;
                newcache->hotbufpages += pages;
                chillbufs(newcache, &newcache->hotqueue,
                    &newcache->hotbufpages);
                TAILQ_INSERT_TAIL(&newcache->hotqueue, bp, b_freelist);
        }
        return bp;
}


void
discard_buffer(struct buf *bp)
{
        splassert(IPL_BIO);

        bufcache_take(bp);
        if (bp->b_vp) {
                RBT_REMOVE(buf_rb_bufs,
                    &bp->b_vp->v_bufs_tree, bp);
                brelvp(bp);
        }
        buf_put(bp);
}

int64_t
bufcache_recover_dmapages(int discard, int64_t howmany)
{
        struct buf *bp = NULL;
        struct bufcache *cache = &cleancache[DMA_CACHE];
        struct bufqueue * queue;
        int64_t recovered = 0;

        splassert(IPL_BIO);

        while ((recovered < howmany) &&
            ((bp = TAILQ_FIRST(&cache->coldqueue)) ||
            (bp = TAILQ_FIRST(&cache->warmqueue)) ||
            (bp = TAILQ_FIRST(&cache->hotqueue)))) {
                int64_t pages = atop(bp->b_bufsize);
                struct bufcache *newcache;

                if (discard || DMA_CACHE >= NUM_CACHES - 1) {
                        discard_buffer(bp);
                        continue;
                }
                KASSERT(bp->cache == DMA_CACHE);

                /*
                 * If this buffer was warm before, move it to
                 * the hot queue in the next cache
                 */

                /*
                 * One way or another, the pages for this
                 * buffer are leaving DMA memory
                 */
                recovered += pages;

                if (!fliphigh) {
                        discard_buffer(bp);
                        continue;
                }

                /*
                 * If we are in the DMA cache, try to flip the
                 * buffer up high to move it on to the other
                 * caches. if we can't move the buffer to high
                 * memory without sleeping, we give it up
                 * now rather than fight for more memory
                 * against non buffer cache competitors.
                 */
                SET(bp->b_flags, B_BUSY);
                if (bp->cache == 0 && buf_flip_high(bp) == -1) {
                        CLR(bp->b_flags, B_BUSY);
                        discard_buffer(bp);
                        continue;
                }
                CLR(bp->b_flags, B_BUSY);

                /*
                 * Move the buffer to the hot queue in the next cache
                 */
                if (ISSET(bp->b_flags, B_COLD)) {
                        queue = &cache->coldqueue;
                } else if (ISSET(bp->b_flags, B_WARM)) {
                        queue = &cache->warmqueue;
                        cache->warmbufpages -= pages;
                } else {
                        queue = &cache->hotqueue;
                        cache->hotbufpages -= pages;
                }
                TAILQ_REMOVE(queue, bp, b_freelist);
                cache->cachepages -= pages;
                CLR(bp->b_flags, B_WARM);
                CLR(bp->b_flags, B_COLD);
                bp->cache++;
                newcache= &cleancache[bp->cache];
                newcache->cachepages += pages;
                newcache->hotbufpages += pages;
                chillbufs(newcache, &newcache->hotqueue,
                    &newcache->hotbufpages);
                TAILQ_INSERT_TAIL(&newcache->hotqueue, bp, b_freelist);
        }
        return recovered;
}

struct buf *
bufcache_getcleanbuf_range(int start, int end, int discard)
{
        int i, j = start, q = end;
        struct buf *bp = NULL;

        /*
         * XXX in theory we could promote warm buffers into a previous queue
         * so in the pathological case of where we go through all the caches
         * without getting a buffer we have to start at the beginning again.
         */
        while (j <= q)  {
                for (i = q; i >= j; i--)
                        if ((bp = bufcache_getcleanbuf(i, discard)))
                                return (bp);
                j++;
        }
        return bp;
}

struct buf *
bufcache_gethighcleanbuf(void)
{
        if (!fliphigh)
                return NULL;
        return bufcache_getcleanbuf_range(DMA_CACHE + 1, NUM_CACHES - 1, 0);
}

struct buf *
bufcache_getdirtybuf(void)
{
        return TAILQ_FIRST(&dirtyqueue);
}

void
bufcache_take(struct buf *bp)
{
        struct bufqueue *queue;
        int64_t pages;

        splassert(IPL_BIO);
        KASSERT(ISSET(bp->b_flags, B_BC));
        KASSERT(bp->cache >= DMA_CACHE);
        KASSERT((bp->cache < NUM_CACHES));

        pages = atop(bp->b_bufsize);

        TRACEPOINT(vfs, bufcache_take, bp->b_flags, bp->cache, pages);

        struct bufcache *cache = &cleancache[bp->cache];
        if (!ISSET(bp->b_flags, B_DELWRI)) {
                if (ISSET(bp->b_flags, B_COLD)) {
                        queue = &cache->coldqueue;
                } else if (ISSET(bp->b_flags, B_WARM)) {
                        queue = &cache->warmqueue;
                        cache->warmbufpages -= pages;
                } else {
                        queue = &cache->hotqueue;
                        cache->hotbufpages -= pages;
                }
                bcstats.numcleanpages -= pages;
                cache->cachepages -= pages;
        } else {
                queue = &dirtyqueue;
                bcstats.numdirtypages -= pages;
                bcstats.delwribufs--;
        }
        TAILQ_REMOVE(queue, bp, b_freelist);
}

/* move buffers from a hot or warm queue to a cold queue in a cache */
int
chillbufs(struct bufcache *cache, struct bufqueue *queue, int64_t *queuepages)
{
        struct buf *bp;
        int64_t limit, pages;

        /*
         * We limit the hot queue to be small, with a max of 4096 pages.
         * We limit the warm queue to half the cache size.
         *
         * We impose a minimum size of 96 to prevent too much "wobbling".
         */
        if (queue == &cache->hotqueue)
                limit = min(cache->cachepages / 20, 4096);
        else if (queue == &cache->warmqueue)
                limit = (cache->cachepages / 2);
        else
                panic("chillbufs: invalid queue");

        if (*queuepages > 96 && *queuepages > limit) {
                bp = TAILQ_FIRST(queue);
                if (!bp)
                        panic("inconsistent bufpage counts");
                pages = atop(bp->b_bufsize);
                *queuepages -= pages;
                TAILQ_REMOVE(queue, bp, b_freelist);
                /* we do not clear B_WARM */
                SET(bp->b_flags, B_COLD);
                TAILQ_INSERT_TAIL(&cache->coldqueue, bp, b_freelist);
                return 1;
        }
        return 0;
}

void
bufcache_release(struct buf *bp)
{
        struct bufqueue *queue;
        int64_t pages;
        struct bufcache *cache = &cleancache[bp->cache];

        KASSERT(ISSET(bp->b_flags, B_BC));
        pages = atop(bp->b_bufsize);

        TRACEPOINT(vfs, bufcache_rel, bp->b_flags, bp->cache, pages);

        if (fliphigh) {
                if (ISSET(bp->b_flags, B_DMA) && bp->cache > 0)
                        panic("B_DMA buffer release from cache %d",
                            bp->cache);
                else if ((!ISSET(bp->b_flags, B_DMA)) && bp->cache == 0)
                        panic("Non B_DMA buffer release from cache %d",
                            bp->cache);
        }

        if (!ISSET(bp->b_flags, B_DELWRI)) {
                int64_t *queuepages;
                if (ISSET(bp->b_flags, B_WARM | B_COLD)) {
                        SET(bp->b_flags, B_WARM);
                        CLR(bp->b_flags, B_COLD);
                        queue = &cache->warmqueue;
                        queuepages = &cache->warmbufpages;
                } else {
                        queue = &cache->hotqueue;
                        queuepages = &cache->hotbufpages;
                }
                *queuepages += pages;
                bcstats.numcleanpages += pages;
                cache->cachepages += pages;
                chillbufs(cache, queue, queuepages);
        } else {
                queue = &dirtyqueue;
                bcstats.numdirtypages += pages;
                bcstats.delwribufs++;
        }
        TAILQ_INSERT_TAIL(queue, bp, b_freelist);
}

#ifdef HIBERNATE
/*
 * Nuke the buffer cache from orbit when hibernating. We do not want to save
 * any clean cache pages to swap and read them back. the original disk files
 * are just as good.
 */
void
hibernate_suspend_bufcache(void)
{
        struct buf *bp;
        int s;

        s = splbio();
        /* Chuck away all the cache pages.. discard bufs, do not promote */
        while ((bp = bufcache_getcleanbuf_range(DMA_CACHE, NUM_CACHES - 1, 1))) {
                bufcache_take(bp);
                if (bp->b_vp) {
                        RBT_REMOVE(buf_rb_bufs, &bp->b_vp->v_bufs_tree, bp);
                        brelvp(bp);
                }
                buf_put(bp);
        }
        splx(s);
}

void
hibernate_resume_bufcache(void)
{
        /* XXX Nothing needed here for now */
}
#endif /* HIBERNATE */