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MM: alloc_large_system_hash() can free some memory for non power-of-two bucketsize

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alloc_large_system_hash() is called at boot time to allocate space for
several large hash tables.

Lately, TCP hash table was changed and its bucketsize is not a power-of-two
anymore.

On most setups, alloc_large_system_hash() allocates one big page (order >
0) with __get_free_pages(GFP_ATOMIC, order).  This single high_order page
has a power-of-two size, bigger than the needed size.

We can free all pages that wont be used by the hash table.

On a 1GB i386 machine, this patch saves 128 KB of LOWMEM memory.

TCP established hash table entries: 32768 (order: 6, 393216 bytes)

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Eric Dumazet 2007-07-15 23:38:05 -07:00 committed by Linus Torvalds
parent b92151bab9
commit 1037b83bd0
1 changed files with 15 additions and 0 deletions
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15
mm/page_alloc.c
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@ -3584,6 +3584,21 @@ void *__init alloc_large_system_hash(const char *tablename,
for (order = 0; ((1UL << order) << PAGE_SHIFT) < size; order++)
;
table = (void*) __get_free_pages(GFP_ATOMIC, order);
/*
* If bucketsize is not a power-of-two, we may free
* some pages at the end of hash table.
*/
if (table) {
unsigned long alloc_end = (unsigned long)table +
(PAGE_SIZE << order);
unsigned long used = (unsigned long)table +
PAGE_ALIGN(size);
split_page(virt_to_page(table), order);
while (used < alloc_end) {
free_page(used);
used += PAGE_SIZE;
}
}
}
} while (!table && size > PAGE_SIZE && --log2qty);