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
  40 struct rds_page_remainder {
  41         struct page     *r_page;
  42         unsigned long   r_offset;
  43 };
  44
  45 static
  46 DEFINE_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  */
  68 int 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();
 145 out:
 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 }
 151 EXPORT_SYMBOL_GPL(rds_page_remainder_alloc);
 152
 153 void 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 }