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/*
* linux/arch/arm/mm/small_page.c
*
* Copyright (C) 1996 Russell King
*
* Changelog:
* 26/01/1996 RMK Cleaned up various areas to make little more generic
* 07/02/1999 RMK Support added for 16K and 32K page sizes
* containing 8K blocks
*/
#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/ptrace.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/smp.h>
#include <asm/bitops.h>
#include <asm/pgtable.h>
#define PEDANTIC
/*
* Requirement:
* We need to be able to allocate naturally aligned memory of finer
* granularity than the page size. This is typically used for the
* second level page tables on 32-bit ARMs.
*
* Theory:
* We "misuse" the Linux memory management system. We use alloc_page
* to allocate a page and then mark it as reserved. The Linux memory
* management system will then ignore the "offset", "next_hash" and
* "pprev_hash" entries in the mem_map for this page.
*
* We then use a bitstring in the "offset" field to mark which segments
* of the page are in use, and manipulate this as required during the
* allocation and freeing of these small pages.
*
* We also maintain a queue of pages being used for this purpose using
* the "next_hash" and "pprev_hash" entries of mem_map;
*/
struct order {
struct page *queue;
unsigned int mask; /* (1 << shift) - 1 */
unsigned int shift; /* (1 << shift) size of page */
unsigned int block_mask; /* nr_blocks - 1 */
unsigned int all_used; /* (1 << nr_blocks) - 1 */
};
static struct order orders[] = {
#if PAGE_SIZE == 4096
{ NULL, 2047, 11, 1, 0x00000003 }
#elif PAGE_SIZE == 32768
{ NULL, 2047, 11, 15, 0x0000ffff },
{ NULL, 8191, 13, 3, 0x0000000f }
#else
#error unsupported page size
#endif
};
#define USED_MAP(pg) ((pg)->index)
#define TEST_AND_CLEAR_USED(pg,off) (test_and_clear_bit(off, &USED_MAP(pg)))
#define SET_USED(pg,off) (set_bit(off, &USED_MAP(pg)))
static void add_page_to_queue(struct page *page, struct page **p)
{
#ifdef PEDANTIC
if (page->pprev_hash)
PAGE_BUG(page);
#endif
page->next_hash = *p;
if (*p)
(*p)->pprev_hash = &page->next_hash;
*p = page;
page->pprev_hash = p;
}
static void remove_page_from_queue(struct page *page)
{
if (page->pprev_hash) {
if (page->next_hash)
page->next_hash->pprev_hash = page->pprev_hash;
*page->pprev_hash = page->next_hash;
page->pprev_hash = NULL;
}
}
static unsigned long __get_small_page(int priority, struct order *order)
{
unsigned long flags;
struct page *page;
int offset;
save_flags(flags);
if (!order->queue)
goto need_new_page;
cli();
page = order->queue;
again:
#ifdef PEDANTIC
if (USED_MAP(page) & ~order->all_used)
PAGE_BUG(page);
#endif
offset = ffz(USED_MAP(page));
SET_USED(page, offset);
if (USED_MAP(page) == order->all_used)
remove_page_from_queue(page);
restore_flags(flags);
return page_address(page) + (offset << order->shift);
need_new_page:
page = alloc_page(priority);
if (!order->queue) {
if (!page)
goto no_page;
SetPageReserved(page);
USED_MAP(page) = 0;
cli();
add_page_to_queue(page, &order->queue);
} else {
__free_page(page);
cli();
page = order->queue;
}
goto again;
no_page:
restore_flags(flags);
return 0;
}
static void __free_small_page(unsigned long spage, struct order *order)
{
unsigned long flags;
unsigned long nr;
struct page *page;
nr = MAP_NR(spage);
if (nr < max_mapnr) {
page = mem_map + nr;
/*
* The container-page must be marked Reserved
*/
if (!PageReserved(page) || spage & order->mask)
goto non_small;
#ifdef PEDANTIC
if (USED_MAP(page) & ~order->all_used)
PAGE_BUG(page);
#endif
spage = spage >> order->shift;
spage &= order->block_mask;
/*
* the following must be atomic wrt get_page
*/
save_flags_cli(flags);
if (USED_MAP(page) == order->all_used)
add_page_to_queue(page, &order->queue);
if (!TEST_AND_CLEAR_USED(page, spage))
goto already_free;
if (USED_MAP(page) == 0)
goto free_page;
restore_flags(flags);
}
return;
free_page:
/*
* unlink the page from the small page queue and free it
*/
remove_page_from_queue(page);
restore_flags(flags);
ClearPageReserved(page);
__free_page(page);
return;
non_small:
printk("Trying to free non-small page from %p\n", __builtin_return_address(0));
return;
already_free:
printk("Trying to free free small page from %p\n", __builtin_return_address(0));
}
unsigned long get_page_2k(int priority)
{
return __get_small_page(priority, orders+0);
}
void free_page_2k(unsigned long spage)
{
__free_small_page(spage, orders+0);
}
#if PAGE_SIZE > 8192
unsigned long get_page_8k(int priority)
{
return __get_small_page(priority, orders+1);
}
void free_page_8k(unsigned long spage)
{
__free_small_page(spage, orders+1);
}
#endif
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