From 1037b83bd04e31449dc9323f1e8ddada4264ef66 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Sun, 15 Jul 2007 23:38:05 -0700 Subject: [PATCH] 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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/page_alloc.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 092b2d8f2f0..8dadda6e1fe 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -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); -- 2.20.1