page.c

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/*
 * 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;
};

static DEFINE_PER_CPU_SHARED_ALIGNED(struct rds_page_remainder,
                     rds_page_remainders);

/*
 * returns 0 on success or -errno on failure.
 *
 * We don't have to worry about flush_dcache_page() as this only works
 * with private pages.  If, say, we were to do directed receive to pinned
 * user pages we'd have to worry more about cache coherence.  (Though
 * the flush_dcache_page() in get_user_pages() would probably be enough).
 */
int rds_page_copy_user(struct page *page, unsigned long offset,
               void __user *ptr, unsigned long bytes,
               int to_user)
{
    unsigned long ret;
    void *addr;

    addr = kmap(page);
    if (to_user) {
        rds_stats_add(s_copy_to_user, bytes);
        ret = copy_to_user(ptr, addr + offset, bytes);
    } else {
        rds_stats_add(s_copy_from_user, bytes);
        ret = copy_from_user(addr + offset, ptr, bytes);
    }
    kunmap(page);

    return ret ? -EFAULT : 0;
}
EXPORT_SYMBOL_GPL(rds_page_copy_user);

int rds_page_remainder_alloc(struct scatterlist *scat, unsigned long bytes,
                 gfp_t gfp)
{
    struct rds_page_remainder *rem;
    unsigned long flags;
    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;
    }

    rem = &per_cpu(rds_page_remainders, get_cpu());
    local_irq_save(flags);

    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 += bytes;
            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_irq_restore(flags);
        put_cpu();

        page = alloc_page(gfp);

        rem = &per_cpu(rds_page_remainders, get_cpu());
        local_irq_save(flags);

        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_irq_restore(flags);
    put_cpu();
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);

static int rds_page_remainder_cpu_notify(struct notifier_block *self,
                     unsigned long action, void *hcpu)
{
    struct rds_page_remainder *rem;
    long cpu = (long)hcpu;

    rem = &per_cpu(rds_page_remainders, cpu);

    rdsdebug("cpu %ld action 0x%lx\n", cpu, action);

    switch (action) {
    case CPU_DEAD:
        if (rem->r_page)
            __free_page(rem->r_page);
        rem->r_page = NULL;
        break;
    }

    return 0;
}

static struct notifier_block rds_page_remainder_nb = {
    .notifier_call = rds_page_remainder_cpu_notify,
};

void rds_page_exit(void)
{
    int i;

    for_each_possible_cpu(i)
        rds_page_remainder_cpu_notify(&rds_page_remainder_nb,
                          (unsigned long)CPU_DEAD,
                          (void *)(long)i);
}