// SPDX-License-Identifier: GPL-2.0
/*
 *  linux/mm/page_io.c
 *
 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *
 *  Swap reorganised 29.12.95, 
 *  Asynchronous swapping added 30.12.95. Stephen Tweedie
 *  Removed race in async swapping. 14.4.1996. Bruno Haible
 *  Add swap of shared pages through the page cache. 20.2.1998. Stephen Tweedie
 *  Always use brw_page, life becomes simpler. 12 May 1998 Eric Biederman
 */

#include <linux/mm.h>
#include <linux/kernel_stat.h>
#include <linux/gfp.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/bio.h>
#include <linux/swapops.h>
#include <linux/writeback.h>
#include <linux/blkdev.h>
#include <linux/psi.h>
#include <linux/uio.h>
#include <linux/sched/task.h>
#include <linux/delayacct.h>
#include <linux/zswap.h>
#include "swap.h"

static void __end_swap_bio_write(struct bio *bio)
{
        struct folio *folio = bio_first_folio_all(bio);

        if (bio->bi_status) {
                /*
                 * We failed to write the page out to swap-space.
                 * Re-dirty the page in order to avoid it being reclaimed.
                 * Also print a dire warning that things will go BAD (tm)
                 * very quickly.
                 *
                 * Also clear PG_reclaim to avoid folio_rotate_reclaimable()
                 */
                folio_mark_dirty(folio);
                pr_alert_ratelimited("Write-error on swap-device (%u:%u:%llu)\n",
                                     MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),
                                     (unsigned long long)bio->bi_iter.bi_sector);
                folio_clear_reclaim(folio);
        }
        folio_end_writeback(folio);
}

static void end_swap_bio_write(struct bio *bio)
{
        __end_swap_bio_write(bio);
        bio_put(bio);
}

static void __end_swap_bio_read(struct bio *bio)
{
        struct folio *folio = bio_first_folio_all(bio);

        if (bio->bi_status) {
                pr_alert_ratelimited("Read-error on swap-device (%u:%u:%llu)\n",
                                     MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),
                                     (unsigned long long)bio->bi_iter.bi_sector);
        } else {
                folio_mark_uptodate(folio);
        }
        folio_unlock(folio);
}

static void end_swap_bio_read(struct bio *bio)
{
        __end_swap_bio_read(bio);
        bio_put(bio);
}

int generic_swapfile_activate(struct swap_info_struct *sis,
                                struct file *swap_file,
                                sector_t *span)
{
        struct address_space *mapping = swap_file->f_mapping;
        struct inode *inode = mapping->host;
        unsigned blocks_per_page;
        unsigned long page_no;
        unsigned blkbits;
        sector_t probe_block;
        sector_t last_block;
        sector_t lowest_block = -1;
        sector_t highest_block = 0;
        int nr_extents = 0;
        int ret;

        blkbits = inode->i_blkbits;
        blocks_per_page = PAGE_SIZE >> blkbits;

        /*
         * Map all the blocks into the extent tree.  This code doesn't try
         * to be very smart.
         */
        probe_block = 0;
        page_no = 0;
        last_block = i_size_read(inode) >> blkbits;
        while ((probe_block + blocks_per_page) <= last_block &&
                        page_no < sis->max) {
                unsigned block_in_page;
                sector_t first_block;

                cond_resched();

                first_block = probe_block;
                ret = bmap(inode, &first_block);
                if (ret || !first_block)
                        goto bad_bmap;

                /*
                 * It must be PAGE_SIZE aligned on-disk
                 */
                if (first_block & (blocks_per_page - 1)) {
                        probe_block++;
                        goto reprobe;
                }

                for (block_in_page = 1; block_in_page < blocks_per_page;
                                        block_in_page++) {
                        sector_t block;

                        block = probe_block + block_in_page;
                        ret = bmap(inode, &block);
                        if (ret || !block)
                                goto bad_bmap;

                        if (block != first_block + block_in_page) {
                                /* Discontiguity */
                                probe_block++;
                                goto reprobe;
                        }
                }

                first_block >>= (PAGE_SHIFT - blkbits);
                if (page_no) {  /* exclude the header page */
                        if (first_block < lowest_block)
                                lowest_block = first_block;
                        if (first_block > highest_block)
                                highest_block = first_block;
                }

                /*
                 * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
                 */
                ret = add_swap_extent(sis, page_no, 1, first_block);
                if (ret < 0)
                        goto out;
                nr_extents += ret;
                page_no++;
                probe_block += blocks_per_page;
reprobe:
                continue;
        }
        ret = nr_extents;
        *span = 1 + highest_block - lowest_block;
        if (page_no == 0)
                page_no = 1;    /* force Empty message */
        sis->max = page_no;
        sis->pages = page_no - 1;
out:
        return ret;
bad_bmap:
        pr_err("swapon: swapfile has holes\n");
        ret = -EINVAL;
        goto out;
}

static bool is_folio_zero_filled(struct folio *folio)
{
        unsigned int pos, last_pos;
        unsigned long *data;
        unsigned int i;

        last_pos = PAGE_SIZE / sizeof(*data) - 1;
        for (i = 0; i < folio_nr_pages(folio); i++) {
                data = kmap_local_folio(folio, i * PAGE_SIZE);
                /*
                 * Check last word first, incase the page is zero-filled at
                 * the start and has non-zero data at the end, which is common
                 * in real-world workloads.
                 */
                if (data[last_pos]) {
                        kunmap_local(data);
                        return false;
                }
                for (pos = 0; pos < last_pos; pos++) {
                        if (data[pos]) {
                                kunmap_local(data);
                                return false;
                        }
                }
                kunmap_local(data);
        }

        return true;
}

static void swap_zeromap_folio_set(struct folio *folio)
{
        struct obj_cgroup *objcg = get_obj_cgroup_from_folio(folio);
        struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
        int nr_pages = folio_nr_pages(folio);
        swp_entry_t entry;
        unsigned int i;

        for (i = 0; i < folio_nr_pages(folio); i++) {
                entry = page_swap_entry(folio_page(folio, i));
                set_bit(swp_offset(entry), sis->zeromap);
        }

        count_vm_events(SWPOUT_ZERO, nr_pages);
        if (objcg) {
                count_objcg_events(objcg, SWPOUT_ZERO, nr_pages);
                obj_cgroup_put(objcg);
        }
}

static void swap_zeromap_folio_clear(struct folio *folio)
{
        struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
        swp_entry_t entry;
        unsigned int i;

        for (i = 0; i < folio_nr_pages(folio); i++) {
                entry = page_swap_entry(folio_page(folio, i));
                clear_bit(swp_offset(entry), sis->zeromap);
        }
}

/*
 * We may have stale swap cache pages in memory: notice
 * them here and get rid of the unnecessary final write.
 */
int swap_writeout(struct folio *folio, struct swap_iocb **swap_plug)
{
        int ret = 0;

        if (folio_free_swap(folio))
                goto out_unlock;

        /*
         * Arch code may have to preserve more data than just the page
         * contents, e.g. memory tags.
         */
        ret = arch_prepare_to_swap(folio);
        if (ret) {
                folio_mark_dirty(folio);
                goto out_unlock;
        }

        /*
         * Use a bitmap (zeromap) to avoid doing IO for zero-filled pages.
         * The bits in zeromap are protected by the locked swapcache folio
         * and atomic updates are used to protect against read-modify-write
         * corruption due to other zero swap entries seeing concurrent updates.
         */
        if (is_folio_zero_filled(folio)) {
                swap_zeromap_folio_set(folio);
                goto out_unlock;
        }

        /*
         * Clear bits this folio occupies in the zeromap to prevent zero data
         * being read in from any previous zero writes that occupied the same
         * swap entries.
         */
        swap_zeromap_folio_clear(folio);

        if (zswap_store(folio)) {
                count_mthp_stat(folio_order(folio), MTHP_STAT_ZSWPOUT);
                goto out_unlock;
        }
        if (!mem_cgroup_zswap_writeback_enabled(folio_memcg(folio))) {
                folio_mark_dirty(folio);
                return AOP_WRITEPAGE_ACTIVATE;
        }

        __swap_writepage(folio, swap_plug);
        return 0;
out_unlock:
        folio_unlock(folio);
        return ret;
}

static inline void count_swpout_vm_event(struct folio *folio)
{
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
        if (unlikely(folio_test_pmd_mappable(folio))) {
                count_memcg_folio_events(folio, THP_SWPOUT, 1);
                count_vm_event(THP_SWPOUT);
        }
#endif
        count_mthp_stat(folio_order(folio), MTHP_STAT_SWPOUT);
        count_memcg_folio_events(folio, PSWPOUT, folio_nr_pages(folio));
        count_vm_events(PSWPOUT, folio_nr_pages(folio));
}

#if defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
static void bio_associate_blkg_from_page(struct bio *bio, struct folio *folio)
{
        struct cgroup_subsys_state *css;
        struct mem_cgroup *memcg;

        memcg = folio_memcg(folio);
        if (!memcg)
                return;

        rcu_read_lock();
        css = cgroup_e_css(memcg->css.cgroup, &io_cgrp_subsys);
        bio_associate_blkg_from_css(bio, css);
        rcu_read_unlock();
}
#else
#define bio_associate_blkg_from_page(bio, folio)                do { } while (0)
#endif /* CONFIG_MEMCG && CONFIG_BLK_CGROUP */

struct swap_iocb {
        struct kiocb            iocb;
        struct bio_vec          bvec[SWAP_CLUSTER_MAX];
        int                     pages;
        int                     len;
};
static mempool_t *sio_pool;

int sio_pool_init(void)
{
        if (!sio_pool) {
                mempool_t *pool = mempool_create_kmalloc_pool(
                        SWAP_CLUSTER_MAX, sizeof(struct swap_iocb));
                if (cmpxchg(&sio_pool, NULL, pool))
                        mempool_destroy(pool);
        }
        if (!sio_pool)
                return -ENOMEM;
        return 0;
}

static void sio_write_complete(struct kiocb *iocb, long ret)
{
        struct swap_iocb *sio = container_of(iocb, struct swap_iocb, iocb);
        struct page *page = sio->bvec[0].bv_page;
        int p;

        if (ret != sio->len) {
                /*
                 * In the case of swap-over-nfs, this can be a
                 * temporary failure if the system has limited
                 * memory for allocating transmit buffers.
                 * Mark the page dirty and avoid
                 * folio_rotate_reclaimable but rate-limit the
                 * messages.
                 */
                pr_err_ratelimited("Write error %ld on dio swapfile (%llu)\n",
                                   ret, swap_dev_pos(page_swap_entry(page)));
                for (p = 0; p < sio->pages; p++) {
                        page = sio->bvec[p].bv_page;
                        set_page_dirty(page);
                        ClearPageReclaim(page);
                }
        }

        for (p = 0; p < sio->pages; p++)
                end_page_writeback(sio->bvec[p].bv_page);

        mempool_free(sio, sio_pool);
}

static void swap_writepage_fs(struct folio *folio, struct swap_iocb **swap_plug)
{
        struct swap_iocb *sio = swap_plug ? *swap_plug : NULL;
        struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
        struct file *swap_file = sis->swap_file;
        loff_t pos = swap_dev_pos(folio->swap);

        count_swpout_vm_event(folio);
        folio_start_writeback(folio);
        folio_unlock(folio);
        if (sio) {
                if (sio->iocb.ki_filp != swap_file ||
                    sio->iocb.ki_pos + sio->len != pos) {
                        swap_write_unplug(sio);
                        sio = NULL;
                }
        }
        if (!sio) {
                sio = mempool_alloc(sio_pool, GFP_NOIO);
                init_sync_kiocb(&sio->iocb, swap_file);
                sio->iocb.ki_complete = sio_write_complete;
                sio->iocb.ki_pos = pos;
                sio->pages = 0;
                sio->len = 0;
        }
        bvec_set_folio(&sio->bvec[sio->pages], folio, folio_size(folio), 0);
        sio->len += folio_size(folio);
        sio->pages += 1;
        if (sio->pages == ARRAY_SIZE(sio->bvec) || !swap_plug) {
                swap_write_unplug(sio);
                sio = NULL;
        }
        if (swap_plug)
                *swap_plug = sio;
}

static void swap_writepage_bdev_sync(struct folio *folio,
                struct swap_info_struct *sis)
{
        struct bio_vec bv;
        struct bio bio;

        bio_init(&bio, sis->bdev, &bv, 1, REQ_OP_WRITE | REQ_SWAP);
        bio.bi_iter.bi_sector = swap_folio_sector(folio);
        bio_add_folio_nofail(&bio, folio, folio_size(folio), 0);

        bio_associate_blkg_from_page(&bio, folio);
        count_swpout_vm_event(folio);

        folio_start_writeback(folio);
        folio_unlock(folio);

        submit_bio_wait(&bio);
        __end_swap_bio_write(&bio);
}

static void swap_writepage_bdev_async(struct folio *folio,
                struct swap_info_struct *sis)
{
        struct bio *bio;

        bio = bio_alloc(sis->bdev, 1, REQ_OP_WRITE | REQ_SWAP, GFP_NOIO);
        bio->bi_iter.bi_sector = swap_folio_sector(folio);
        bio->bi_end_io = end_swap_bio_write;
        bio_add_folio_nofail(bio, folio, folio_size(folio), 0);

        bio_associate_blkg_from_page(bio, folio);
        count_swpout_vm_event(folio);
        folio_start_writeback(folio);
        folio_unlock(folio);
        submit_bio(bio);
}

void __swap_writepage(struct folio *folio, struct swap_iocb **swap_plug)
{
        struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);

        VM_BUG_ON_FOLIO(!folio_test_swapcache(folio), folio);
        /*
         * ->flags can be updated non-atomically (scan_swap_map_slots),
         * but that will never affect SWP_FS_OPS, so the data_race
         * is safe.
         */
        if (data_race(sis->flags & SWP_FS_OPS))
                swap_writepage_fs(folio, swap_plug);
        /*
         * ->flags can be updated non-atomically (scan_swap_map_slots),
         * but that will never affect SWP_SYNCHRONOUS_IO, so the data_race
         * is safe.
         */
        else if (data_race(sis->flags & SWP_SYNCHRONOUS_IO))
                swap_writepage_bdev_sync(folio, sis);
        else
                swap_writepage_bdev_async(folio, sis);
}

void swap_write_unplug(struct swap_iocb *sio)
{
        struct iov_iter from;
        struct address_space *mapping = sio->iocb.ki_filp->f_mapping;
        int ret;

        iov_iter_bvec(&from, ITER_SOURCE, sio->bvec, sio->pages, sio->len);
        ret = mapping->a_ops->swap_rw(&sio->iocb, &from);
        if (ret != -EIOCBQUEUED)
                sio_write_complete(&sio->iocb, ret);
}

static void sio_read_complete(struct kiocb *iocb, long ret)
{
        struct swap_iocb *sio = container_of(iocb, struct swap_iocb, iocb);
        int p;

        if (ret == sio->len) {
                for (p = 0; p < sio->pages; p++) {
                        struct folio *folio = page_folio(sio->bvec[p].bv_page);

                        count_mthp_stat(folio_order(folio), MTHP_STAT_SWPIN);
                        count_memcg_folio_events(folio, PSWPIN, folio_nr_pages(folio));
                        folio_mark_uptodate(folio);
                        folio_unlock(folio);
                }
                count_vm_events(PSWPIN, sio->pages);
        } else {
                for (p = 0; p < sio->pages; p++) {
                        struct folio *folio = page_folio(sio->bvec[p].bv_page);

                        folio_unlock(folio);
                }
                pr_alert_ratelimited("Read-error on swap-device\n");
        }
        mempool_free(sio, sio_pool);
}

static bool swap_read_folio_zeromap(struct folio *folio)
{
        int nr_pages = folio_nr_pages(folio);
        struct obj_cgroup *objcg;
        bool is_zeromap;

        /*
         * Swapping in a large folio that is partially in the zeromap is not
         * currently handled. Return true without marking the folio uptodate so
         * that an IO error is emitted (e.g. do_swap_page() will sigbus).
         */
        if (WARN_ON_ONCE(swap_zeromap_batch(folio->swap, nr_pages,
                        &is_zeromap) != nr_pages))
                return true;

        if (!is_zeromap)
                return false;

        objcg = get_obj_cgroup_from_folio(folio);
        count_vm_events(SWPIN_ZERO, nr_pages);
        if (objcg) {
                count_objcg_events(objcg, SWPIN_ZERO, nr_pages);
                obj_cgroup_put(objcg);
        }

        folio_zero_range(folio, 0, folio_size(folio));
        folio_mark_uptodate(folio);
        return true;
}

static void swap_read_folio_fs(struct folio *folio, struct swap_iocb **plug)
{
        struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
        struct swap_iocb *sio = NULL;
        loff_t pos = swap_dev_pos(folio->swap);

        if (plug)
                sio = *plug;
        if (sio) {
                if (sio->iocb.ki_filp != sis->swap_file ||
                    sio->iocb.ki_pos + sio->len != pos) {
                        swap_read_unplug(sio);
                        sio = NULL;
                }
        }
        if (!sio) {
                sio = mempool_alloc(sio_pool, GFP_KERNEL);
                init_sync_kiocb(&sio->iocb, sis->swap_file);
                sio->iocb.ki_pos = pos;
                sio->iocb.ki_complete = sio_read_complete;
                sio->pages = 0;
                sio->len = 0;
        }
        bvec_set_folio(&sio->bvec[sio->pages], folio, folio_size(folio), 0);
        sio->len += folio_size(folio);
        sio->pages += 1;
        if (sio->pages == ARRAY_SIZE(sio->bvec) || !plug) {
                swap_read_unplug(sio);
                sio = NULL;
        }
        if (plug)
                *plug = sio;
}

static void swap_read_folio_bdev_sync(struct folio *folio,
                struct swap_info_struct *sis)
{
        struct bio_vec bv;
        struct bio bio;

        bio_init(&bio, sis->bdev, &bv, 1, REQ_OP_READ);
        bio.bi_iter.bi_sector = swap_folio_sector(folio);
        bio_add_folio_nofail(&bio, folio, folio_size(folio), 0);
        /*
         * Keep this task valid during swap readpage because the oom killer may
         * attempt to access it in the page fault retry time check.
         */
        get_task_struct(current);
        count_mthp_stat(folio_order(folio), MTHP_STAT_SWPIN);
        count_memcg_folio_events(folio, PSWPIN, folio_nr_pages(folio));
        count_vm_events(PSWPIN, folio_nr_pages(folio));
        submit_bio_wait(&bio);
        __end_swap_bio_read(&bio);
        put_task_struct(current);
}

static void swap_read_folio_bdev_async(struct folio *folio,
                struct swap_info_struct *sis)
{
        struct bio *bio;

        bio = bio_alloc(sis->bdev, 1, REQ_OP_READ, GFP_KERNEL);
        bio->bi_iter.bi_sector = swap_folio_sector(folio);
        bio->bi_end_io = end_swap_bio_read;
        bio_add_folio_nofail(bio, folio, folio_size(folio), 0);
        count_mthp_stat(folio_order(folio), MTHP_STAT_SWPIN);
        count_memcg_folio_events(folio, PSWPIN, folio_nr_pages(folio));
        count_vm_events(PSWPIN, folio_nr_pages(folio));
        submit_bio(bio);
}

void swap_read_folio(struct folio *folio, struct swap_iocb **plug)
{
        struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
        bool synchronous = sis->flags & SWP_SYNCHRONOUS_IO;
        bool workingset = folio_test_workingset(folio);
        unsigned long pflags;
        bool in_thrashing;

        VM_BUG_ON_FOLIO(!folio_test_swapcache(folio) && !synchronous, folio);
        VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
        VM_BUG_ON_FOLIO(folio_test_uptodate(folio), folio);

        /*
         * Count submission time as memory stall and delay. When the device
         * is congested, or the submitting cgroup IO-throttled, submission
         * can be a significant part of overall IO time.
         */
        if (workingset) {
                delayacct_thrashing_start(&in_thrashing);
                psi_memstall_enter(&pflags);
        }
        delayacct_swapin_start();

        if (swap_read_folio_zeromap(folio)) {
                folio_unlock(folio);
                goto finish;
        }

        if (zswap_load(folio) != -ENOENT)
                goto finish;

        /* We have to read from slower devices. Increase zswap protection. */
        zswap_folio_swapin(folio);

        if (data_race(sis->flags & SWP_FS_OPS)) {
                swap_read_folio_fs(folio, plug);
        } else if (synchronous) {
                swap_read_folio_bdev_sync(folio, sis);
        } else {
                swap_read_folio_bdev_async(folio, sis);
        }

finish:
        if (workingset) {
                delayacct_thrashing_end(&in_thrashing);
                psi_memstall_leave(&pflags);
        }
        delayacct_swapin_end();
}

void __swap_read_unplug(struct swap_iocb *sio)
{
        struct iov_iter from;
        struct address_space *mapping = sio->iocb.ki_filp->f_mapping;
        int ret;

        iov_iter_bvec(&from, ITER_DEST, sio->bvec, sio->pages, sio->len);
        ret = mapping->a_ops->swap_rw(&sio->iocb, &from);
        if (ret != -EIOCBQUEUED)
                sio_read_complete(&sio->iocb, ret);
}