From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 18 May 2007 11:54:54 +0200 From: Eric Dumazet Subject: [PATCH] MM : alloc_large_system_hash() can free some memory for non power-of-two bucketsize Message-Id: <20070518115454.d3e32f4d.dada1@cosmosbay.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton , "linux-mm@kvack.org" Cc: linux kernel , David Miller List-ID: 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 --- diff --git a/mm/page_alloc.c b/mm/page_alloc.c index ae96dd8..2e0ba08 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3350,6 +3350,20 @@ 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); + while (used < alloc_end) { + free_page(used); + used += PAGE_SIZE; + } + } } } while (!table && size > PAGE_SIZE && --log2qty); -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org