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   1 /*
   2  *  linux/arch/arm26/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  *   23/05/2004 IM      Fixed to use struct page->lru (thanks wli)
  16  *
  17  */
  18 #include <linux/signal.h>
  19 #include <linux/sched.h>
  20 #include <linux/kernel.h>
  21 #include <linux/errno.h>
  22 #include <linux/string.h>
  23 #include <linux/types.h>
  24 #include <linux/ptrace.h>
  25 #include <linux/mman.h>
  26 #include <linux/mm.h>
  27 #include <linux/swap.h>
  28 #include <linux/smp.h>
  29 #include <linux/bitops.h>
  30
  31 #include <asm/pgtable.h>
  32
  33 #define PEDANTIC
  34
  35 /*
  36  * Requirement:
  37  *  We need to be able to allocate naturally aligned memory of finer
  38  *  granularity than the page size.  This is typically used for the
  39  *  second level page tables on 32-bit ARMs.
  40  *
  41  * FIXME - this comment is *out of date*
  42  * Theory:
  43  *  We "misuse" the Linux memory management system.  We use alloc_page
  44  *  to allocate a page and then mark it as reserved.  The Linux memory
  45  *  management system will then ignore the "offset", "next_hash" and
  46  *  "pprev_hash" entries in the mem_map for this page.
  47  *
  48  *  We then use a bitstring in the "offset" field to mark which segments
  49  *  of the page are in use, and manipulate this as required during the
  50  *  allocation and freeing of these small pages.
  51  *
  52  *  We also maintain a queue of pages being used for this purpose using
  53  *  the "next_hash" and "pprev_hash" entries of mem_map;
  54  */
  55
  56 struct order {
  57         struct list_head queue;
  58         unsigned int mask;              /* (1 << shift) - 1             */
  59         unsigned int shift;             /* (1 << shift) size of page    */
  60         unsigned int block_mask;        /* nr_blocks - 1                */
  61         unsigned int all_used;          /* (1 << nr_blocks) - 1         */
  62 };
  63
  64
  65 static struct order orders[] = {
  66 #if PAGE_SIZE == 32768
  67         { LIST_HEAD_INIT(orders[0].queue), 2047, 11, 15, 0x0000ffff },
  68         { LIST_HEAD_INIT(orders[1].queue), 8191, 13,  3, 0x0000000f }
  69 #else
  70 #error unsupported page size (ARGH!)
  71 #endif
  72 };
  73
  74 #define USED_MAP(pg)                    ((pg)->index)
  75 #define TEST_AND_CLEAR_USED(pg,off)     (test_and_clear_bit(off, &USED_MAP(pg)))
  76 #define SET_USED(pg,off)                (set_bit(off, &USED_MAP(pg)))
  77
  78 static DEFINE_SPINLOCK(small_page_lock);
  79
  80 static unsigned long __get_small_page(int priority, struct order *order)
  81 {
  82         unsigned long flags;
  83         struct page *page;
  84         int offset;
  85
  86         do {
  87                 spin_lock_irqsave(&small_page_lock, flags);
  88
  89                 if (list_empty(&order->queue))
  90                         goto need_new_page;
  91
  92                 page = list_entry(order->queue.next, struct page, lru);
  93 again:
  94 #ifdef PEDANTIC
  95                 BUG_ON(USED_MAP(page) & ~order->all_used);
  96 #endif
  97                 offset = ffz(USED_MAP(page));
  98                 SET_USED(page, offset);
  99                 if (USED_MAP(page) == order->all_used)
 100                         list_del_init(&page->lru);
 101                 spin_unlock_irqrestore(&small_page_lock, flags);
 102
 103                 return (unsigned long) page_address(page) + (offset << order->shift);
 104
 105 need_new_page:
 106                 spin_unlock_irqrestore(&small_page_lock, flags);
 107                 page = alloc_page(priority);
 108                 spin_lock_irqsave(&small_page_lock, flags);
 109
 110                 if (list_empty(&order->queue)) {
 111                         if (!page)
 112                                 goto no_page;
 113                         SetPageReserved(page);
 114                         USED_MAP(page) = 0;
 115                         list_add(&page->lru, &order->queue);
 116                         goto again;
 117                 }
 118
 119                 spin_unlock_irqrestore(&small_page_lock, flags);
 120                 __free_page(page);
 121         } while (1);
 122
 123 no_page:
 124         spin_unlock_irqrestore(&small_page_lock, flags);
 125         return 0;
 126 }
 127
 128 static void __free_small_page(unsigned long spage, struct order *order)
 129 {
 130         unsigned long flags;
 131         struct page *page;
 132
 133         if (virt_addr_valid(spage)) {
 134                 page = virt_to_page(spage);
 135
 136                 /*
 137                  * The container-page must be marked Reserved
 138                  */
 139                 if (!PageReserved(page) || spage & order->mask)
 140                         goto non_small;
 141
 142 #ifdef PEDANTIC
 143                 BUG_ON(USED_MAP(page) & ~order->all_used);
 144 #endif
 145
 146                 spage = spage >> order->shift;
 147                 spage &= order->block_mask;
 148
 149                 /*
 150                  * the following must be atomic wrt get_page
 151                  */
 152                 spin_lock_irqsave(&small_page_lock, flags);
 153
 154                 if (USED_MAP(page) == order->all_used)
 155                         list_add(&page->lru, &order->queue);
 156
 157                 if (!TEST_AND_CLEAR_USED(page, spage))
 158                         goto already_free;
 159
 160                 if (USED_MAP(page) == 0)
 161                         goto free_page;
 162
 163                 spin_unlock_irqrestore(&small_page_lock, flags);
 164         }
 165         return;
 166
 167 free_page:
 168         /*
 169          * unlink the page from the small page queue and free it
 170          */
 171         list_del_init(&page->lru);
 172         spin_unlock_irqrestore(&small_page_lock, flags);
 173         ClearPageReserved(page);
 174         __free_page(page);
 175         return;
 176
 177 non_small:
 178         printk("Trying to free non-small page from %p\n", __builtin_return_address(0));
 179         return;
 180 already_free:
 181         printk("Trying to free free small page from %p\n", __builtin_return_address(0));
 182 }
 183
 184 unsigned long get_page_8k(int priority)
 185 {
 186         return __get_small_page(priority, orders+1);
 187 }
 188
 189 void free_page_8k(unsigned long spage)
 190 {
 191         __free_small_page(spage, orders+1);
 192 }