/*
 * Copyright (c) 2006 Oracle.  All rights reserved.
 *
 * This software is available to you under a choice of one of two
 * licenses.  You may choose to be licensed under the terms of the GNU
 * General Public License (GPL) Version 2, available from the file
 * COPYING in the main directory of this source tree, or the
 * OpenIB.org BSD license below:
 *
 *     Redistribution and use in source and binary forms, with or
 *     without modification, are permitted provided that the following
 *     conditions are met:
 *
 *      - Redistributions of source code must retain the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer.
 *
 *      - 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.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 */
#include <linux/highmem.h>
#include <linux/gfp.h>
#include <linux/cpu.h>
#include <linux/export.h>

#include "rds.h"

struct rds_page_remainder {
        struct page     *r_page;
        unsigned long   r_offset;
        local_lock_t    bh_lock;
};

static DEFINE_PER_CPU_SHARED_ALIGNED(struct rds_page_remainder, rds_page_remainders) = {
        .bh_lock = INIT_LOCAL_LOCK(bh_lock),
};

/**
 * rds_page_remainder_alloc - build up regions of a message.
 *
 * @scat: Scatter list for message
 * @bytes: the number of bytes needed.
 * @gfp: the waiting behaviour of the allocation
 *
 * @gfp is always ored with __GFP_HIGHMEM.  Callers must be prepared to
 * kmap the pages, etc.
 *
 * If @bytes is at least a full page then this just returns a page from
 * alloc_page().
 *
 * If @bytes is a partial page then this stores the unused region of the
 * page in a per-cpu structure.  Future partial-page allocations may be
 * satisfied from that cached region.  This lets us waste less memory on
 * small allocations with minimal complexity.  It works because the transmit
 * path passes read-only page regions down to devices.  They hold a page
 * reference until they are done with the region.
 */
int rds_page_remainder_alloc(struct scatterlist *scat, unsigned long bytes,
                             gfp_t gfp)
{
        struct rds_page_remainder *rem;
        struct page *page;
        int ret;

        gfp |= __GFP_HIGHMEM;

        /* jump straight to allocation if we're trying for a huge page */
        if (bytes >= PAGE_SIZE) {
                page = alloc_page(gfp);
                if (!page) {
                        ret = -ENOMEM;
                } else {
                        sg_set_page(scat, page, PAGE_SIZE, 0);
                        ret = 0;
                }
                goto out;
        }

        local_bh_disable();
        local_lock_nested_bh(&rds_page_remainders.bh_lock);
        rem = this_cpu_ptr(&rds_page_remainders);

        while (1) {
                /* avoid a tiny region getting stuck by tossing it */
                if (rem->r_page && bytes > (PAGE_SIZE - rem->r_offset)) {
                        rds_stats_inc(s_page_remainder_miss);
                        __free_page(rem->r_page);
                        rem->r_page = NULL;
                }

                /* hand out a fragment from the cached page */
                if (rem->r_page && bytes <= (PAGE_SIZE - rem->r_offset)) {
                        sg_set_page(scat, rem->r_page, bytes, rem->r_offset);
                        get_page(sg_page(scat));

                        if (rem->r_offset != 0)
                                rds_stats_inc(s_page_remainder_hit);

                        rem->r_offset += ALIGN(bytes, 8);
                        if (rem->r_offset >= PAGE_SIZE) {
                                __free_page(rem->r_page);
                                rem->r_page = NULL;
                        }
                        ret = 0;
                        break;
                }

                /* alloc if there is nothing for us to use */
                local_unlock_nested_bh(&rds_page_remainders.bh_lock);
                local_bh_enable();

                page = alloc_page(gfp);

                local_bh_disable();
                local_lock_nested_bh(&rds_page_remainders.bh_lock);
                rem = this_cpu_ptr(&rds_page_remainders);

                if (!page) {
                        ret = -ENOMEM;
                        break;
                }

                /* did someone race to fill the remainder before us? */
                if (rem->r_page) {
                        __free_page(page);
                        continue;
                }

                /* otherwise install our page and loop around to alloc */
                rem->r_page = page;
                rem->r_offset = 0;
        }

        local_unlock_nested_bh(&rds_page_remainders.bh_lock);
        local_bh_enable();
out:
        rdsdebug("bytes %lu ret %d %p %u %u\n", bytes, ret,
                 ret ? NULL : sg_page(scat), ret ? 0 : scat->offset,
                 ret ? 0 : scat->length);
        return ret;
}
EXPORT_SYMBOL_GPL(rds_page_remainder_alloc);

void rds_page_exit(void)
{
        unsigned int cpu;

        for_each_possible_cpu(cpu) {
                struct rds_page_remainder *rem;

                rem = &per_cpu(rds_page_remainders, cpu);
                rdsdebug("cpu %u\n", cpu);

                if (rem->r_page)
                        __free_page(rem->r_page);
                rem->r_page = NULL;
        }
}