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>
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@ -3584,6 +3584,21 @@ void *__init alloc_large_system_hash(const char *tablename,
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for (order = 0; ((1UL << order) << PAGE_SHIFT) < size; order++)
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;
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table = (void*) __get_free_pages(GFP_ATOMIC, order);
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/*
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* If bucketsize is not a power-of-two, we may free
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* some pages at the end of hash table.
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*/
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if (table) {
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unsigned long alloc_end = (unsigned long)table +
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(PAGE_SIZE << order);
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unsigned long used = (unsigned long)table +
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PAGE_ALIGN(size);
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split_page(virt_to_page(table), order);
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while (used < alloc_end) {
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free_page(used);
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used += PAGE_SIZE;
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}
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}
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}
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} while (!table && size > PAGE_SIZE && --log2qty);
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