arch/arm26/machine/small_page.c

   1 /*
   2  *  linux/arch/arm/mm/small_page.c
   3  *
   4  *  Copyright (C) 1996  Russell King
   5  *  Copyright (C) 2003  Ian Molton
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  *
  11  *  Changelog:
  12  *   26/01/1996 RMK     Cleaned up various areas to make little more generic
  13  *   07/02/1999 RMK     Support added for 16K and 32K page sizes
  14  *                      containing 8K blocks
  15  */
  16 #include <linux/signal.h>
  17 #include <linux/sched.h>
  18 #include <linux/kernel.h>
  19 #include <linux/errno.h>
  20 #include <linux/string.h>
  21 #include <linux/types.h>
  22 #include <linux/ptrace.h>
  23 #include <linux/mman.h>
  24 #include <linux/mm.h>
  25 #include <linux/swap.h>
  26 #include <linux/smp.h>
  27
  28 #include <asm/bitops.h>
  29 #include <asm/pgtable.h>
  30
  31 #define PEDANTIC
  32
  33 /*
  34  * Requirement:
  35  *  We need to be able to allocate naturally aligned memory of finer
  36  *  granularity than the page size.  This is typically used for the
  37  *  second level page tables on 32-bit ARMs.
  38  *
  39  * Theory:
  40  *  We "misuse" the Linux memory management system.  We use alloc_page
  41  *  to allocate a page and then mark it as reserved.  The Linux memory
  42  *  management system will then ignore the "offset", "next_hash" and
  43  *  "pprev_hash" entries in the mem_map for this page.
  44  *
  45  *  We then use a bitstring in the "offset" field to mark which segments
  46  *  of the page are in use, and manipulate this as required during the
  47  *  allocation and freeing of these small pages.
  48  *
  49  *  We also maintain a queue of pages being used for this purpose using
  50  *  the "next_hash" and "pprev_hash" entries of mem_map;
  51  */
  52
  53 struct order {
  54         struct list_head queue;
  55         unsigned int mask;              /* (1 << shift) - 1             */
  56         unsigned int shift;             /* (1 << shift) size of page    */
  57         unsigned int block_mask;        /* nr_blocks - 1                */
  58         unsigned int all_used;          /* (1 << nr_blocks) - 1         */
  59 };
  60
  61
  62 static struct order orders[] = {
  63 #if PAGE_SIZE == 32768
  64         { LIST_HEAD_INIT(orders[0].queue), 2047, 11, 15, 0x0000ffff },
  65         { LIST_HEAD_INIT(orders[1].queue), 8191, 13,  3, 0x0000000f }
  66 #else
  67 #error unsupported page size (ARGH!)
  68 #endif
  69 };
  70
  71 #define USED_MAP(pg)                    ((pg)->index)
  72 #define TEST_AND_CLEAR_USED(pg,off)     (test_and_clear_bit(off, &USED_MAP(pg)))
  73 #define SET_USED(pg,off)                (set_bit(off, &USED_MAP(pg)))
  74
  75 static spinlock_t small_page_lock = SPIN_LOCK_UNLOCKED;
  76
  77 static unsigned long __get_small_page(int priority, struct order *order)
  78 {
  79         unsigned long flags;
  80         struct page *page;
  81         int offset;
  82
  83         do {
  84                 spin_lock_irqsave(&small_page_lock, flags);
  85
  86                 if (list_empty(&order->queue))
  87                         goto need_new_page;
  88
  89                 page = list_entry(order->queue.next, struct page, list);
  90 again:
  91 #ifdef PEDANTIC
  92                 if (USED_MAP(page) & ~order->all_used)
  93                         PAGE_BUG(page);
  94 #endif
  95                 offset = ffz(USED_MAP(page));
  96                 SET_USED(page, offset);
  97                 if (USED_MAP(page) == order->all_used)
  98                         list_del_init(&page->lru);
  99                 spin_unlock_irqrestore(&small_page_lock, flags);
 100
 101                 return (unsigned long) page_address(page) + (offset << order->shift);
 102
 103 need_new_page:
 104                 spin_unlock_irqrestore(&small_page_lock, flags);
 105                 page = alloc_page(priority);
 106                 spin_lock_irqsave(&small_page_lock, flags);
 107
 108                 if (list_empty(&order->queue)) {
 109                         if (!page)
 110                                 goto no_page;
 111                         SetPageReserved(page);
 112                         USED_MAP(page) = 0;
 113                         list_add(&page->lru, &order->queue);
 114                         goto again;
 115                 }
 116
 117                 spin_unlock_irqrestore(&small_page_lock, flags);
 118                 __free_page(page);
 119         } while (1);
 120
 121 no_page:
 122         spin_unlock_irqrestore(&small_page_lock, flags);
 123         return 0;
 124 }
 125
 126 static void __free_small_page(unsigned long spage, struct order *order)
 127 {
 128         unsigned long flags;
 129         struct page *page;
 130
 131         if (virt_addr_valid(spage)) {
 132                 page = virt_to_page(spage);
 133
 134                 /*
 135                  * The container-page must be marked Reserved
 136                  */
 137                 if (!PageReserved(page) || spage & order->mask)
 138                         goto non_small;
 139
 140 #ifdef PEDANTIC
 141                 if (USED_MAP(page) & ~order->all_used)
 142                         PAGE_BUG(page);
 143 #endif
 144
 145                 spage = spage >> order->shift;
 146                 spage &= order->block_mask;
 147
 148                 /*
 149                  * the following must be atomic wrt get_page
 150                  */
 151                 spin_lock_irqsave(&small_page_lock, flags);
 152
 153                 if (USED_MAP(page) == order->all_used)
 154                         list_add(&page->lru, &order->queue);
 155
 156                 if (!TEST_AND_CLEAR_USED(page, spage))
 157                         goto already_free;
 158
 159                 if (USED_MAP(page) == 0)
 160                         goto free_page;
 161
 162                 spin_unlock_irqrestore(&small_page_lock, flags);
 163         }
 164         return;
 165
 166 free_page:
 167         /*
 168          * unlink the page from the small page queue and free it
 169          */
 170         list_del_init(&page->lru);
 171         spin_unlock_irqrestore(&small_page_lock, flags);
 172         ClearPageReserved(page);
 173         __free_page(page);
 174         return;
 175
 176 non_small:
 177         printk("Trying to free non-small page from %p\n", __builtin_return_address(0));
 178         return;
 179 already_free:
 180         printk("Trying to free free small page from %p\n", __builtin_return_address(0));
 181 }
 182
 183 unsigned long get_page_8k(int priority)
 184 {
 185         return __get_small_page(priority, orders+1);
 186 }
 187
 188 void free_page_8k(unsigned long spage)
 189 {
 190         __free_small_page(spage, orders+1);
 191 }