LXR linux/net/rds/page.c

   1/*
   2 * Copyright (c) 2006 Oracle.  All rights reserved.
   3 *
   4 * This software is available to you under a choice of one of two
   5 * licenses.  You may choose to be licensed under the terms of the GNU
   6 * General Public License (GPL) Version 2, available from the file
   7 * COPYING in the main directory of this source tree, or the
   8 * OpenIB.org BSD license below:
   9 *
  10 *     Redistribution and use in source and binary forms, with or
  11 *     without modification, are permitted provided that the following
  12 *     conditions are met:
  13 *
  14 *      - Redistributions of source code must retain the above
  15 *        copyright notice, this list of conditions and the following
  16 *        disclaimer.
  17 *
  18 *      - Redistributions in binary form must reproduce the above
  19 *        copyright notice, this list of conditions and the following
  20 *        disclaimer in the documentation and/or other materials
  21 *        provided with the distribution.
  22 *
  23 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  24 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  25 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  26 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  27 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  28 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  29 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  30 * SOFTWARE.
  31 *
  32 */
  33#include <linux/highmem.h>
  34#include <linux/gfp.h>
  35#include <linux/cpu.h>
  36#include <linux/export.h>
  37
  38#include "rds.h"
  39
  40struct rds_page_remainder {
  41        struct page     *r_page;
  42        unsigned long   r_offset;
  43};
  44
  45static
  46DEFINE_PER_CPU_SHARED_ALIGNED(struct rds_page_remainder, rds_page_remainders);
  47
  48/**
  49 * rds_page_remainder_alloc - build up regions of a message.
  50 *
  51 * @scat: Scatter list for message
  52 * @bytes: the number of bytes needed.
  53 * @gfp: the waiting behaviour of the allocation
  54 *
  55 * @gfp is always ored with __GFP_HIGHMEM.  Callers must be prepared to
  56 * kmap the pages, etc.
  57 *
  58 * If @bytes is at least a full page then this just returns a page from
  59 * alloc_page().
  60 *
  61 * If @bytes is a partial page then this stores the unused region of the
  62 * page in a per-cpu structure.  Future partial-page allocations may be
  63 * satisfied from that cached region.  This lets us waste less memory on
  64 * small allocations with minimal complexity.  It works because the transmit
  65 * path passes read-only page regions down to devices.  They hold a page
  66 * reference until they are done with the region.
  67 */
  68int rds_page_remainder_alloc(struct scatterlist *scat, unsigned long bytes,
  69                             gfp_t gfp)
  70{
  71        struct rds_page_remainder *rem;
  72        unsigned long flags;
  73        struct page *page;
  74        int ret;
  75
  76        gfp |= __GFP_HIGHMEM;
  77
  78        /* jump straight to allocation if we're trying for a huge page */
  79        if (bytes >= PAGE_SIZE) {
  80                page = alloc_page(gfp);
  81                if (!page) {
  82                        ret = -ENOMEM;
  83                } else {
  84                        sg_set_page(scat, page, PAGE_SIZE, 0);
  85                        ret = 0;
  86                }
  87                goto out;
  88        }
  89
  90        rem = &per_cpu(rds_page_remainders, get_cpu());
  91        local_irq_save(flags);
  92
  93        while (1) {
  94                /* avoid a tiny region getting stuck by tossing it */
  95                if (rem->r_page && bytes > (PAGE_SIZE - rem->r_offset)) {
  96                        rds_stats_inc(s_page_remainder_miss);
  97                        __free_page(rem->r_page);
  98                        rem->r_page = NULL;
  99                }
 100
 101                /* hand out a fragment from the cached page */
 102                if (rem->r_page && bytes <= (PAGE_SIZE - rem->r_offset)) {
 103                        sg_set_page(scat, rem->r_page, bytes, rem->r_offset);
 104                        get_page(sg_page(scat));
 105
 106                        if (rem->r_offset != 0)
 107                                rds_stats_inc(s_page_remainder_hit);
 108
 109                        rem->r_offset += ALIGN(bytes, 8);
 110                        if (rem->r_offset >= PAGE_SIZE) {
 111                                __free_page(rem->r_page);
 112                                rem->r_page = NULL;
 113                        }
 114                        ret = 0;
 115                        break;
 116                }
 117
 118                /* alloc if there is nothing for us to use */
 119                local_irq_restore(flags);
 120                put_cpu();
 121
 122                page = alloc_page(gfp);
 123
 124                rem = &per_cpu(rds_page_remainders, get_cpu());
 125                local_irq_save(flags);
 126
 127                if (!page) {
 128                        ret = -ENOMEM;
 129                        break;
 130                }
 131
 132                /* did someone race to fill the remainder before us? */
 133                if (rem->r_page) {
 134                        __free_page(page);
 135                        continue;
 136                }
 137
 138                /* otherwise install our page and loop around to alloc */
 139                rem->r_page = page;
 140                rem->r_offset = 0;
 141        }
 142
 143        local_irq_restore(flags);
 144        put_cpu();
 145out:
 146        rdsdebug("bytes %lu ret %d %p %u %u\n", bytes, ret,
 147                 ret ? NULL : sg_page(scat), ret ? 0 : scat->offset,
 148                 ret ? 0 : scat->length);
 149        return ret;
 150}
 151EXPORT_SYMBOL_GPL(rds_page_remainder_alloc);
 152
 153void rds_page_exit(void)
 154{
 155        unsigned int cpu;
 156
 157        for_each_possible_cpu(cpu) {
 158                struct rds_page_remainder *rem;
 159
 160                rem = &per_cpu(rds_page_remainders, cpu);
 161                rdsdebug("cpu %u\n", cpu);
 162
 163                if (rem->r_page)
 164                        __free_page(rem->r_page);
 165                rem->r_page = NULL;
 166        }
 167}
 168