Commit 1037b83b authored Jul 15, 2007 by Eric Dumazet Committed by Linus Torvalds Jul 16, 2007

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



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>

parent b92151ba

mm/page_alloc.c

+15 −0

Original line number	Diff line number	Diff line
		@@ -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);

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