From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <464F5FE4.2010607@cosmosbay.com> Date: Sat, 19 May 2007 22:36:52 +0200 From: Eric Dumazet MIME-Version: 1.0 Subject: Re: [PATCH] MM : alloc_large_system_hash() can free some memory for non power-of-two bucketsize References: <20070518115454.d3e32f4d.dada1@cosmosbay.com> <20070519013724.3d4b74e0.akpm@linux-foundation.org> <464F3CCF.2070901@cosmosbay.com> <20070519.115442.30184476.davem@davemloft.net> In-Reply-To: <20070519.115442.30184476.davem@davemloft.net> Content-Type: multipart/mixed; boundary="------------000202020007030807040908" Sender: owner-linux-mm@kvack.org Return-Path: To: David Miller , akpm@linux-foundation.org Cc: dhowells@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: This is a multi-part message in MIME format. --------------000202020007030807040908 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit David Miller a ecrit : > From: Eric Dumazet > Date: Sat, 19 May 2007 20:07:11 +0200 > >> Maybe David has an idea how this can be done properly ? >> >> ref : http://marc.info/?l=linux-netdev&m=117706074825048&w=2 > > You need to use __GFP_COMP or similar to make this splitting+freeing > thing work. > > Otherwise the individual pages don't have page references, only > the head page of the high-order page will. > Oh thanks David for the hint. I added a split_page() call and it seems to work now. [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 --------------000202020007030807040908 Content-Type: text/plain; name="alloc_large.patch" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="alloc_large.patch" diff --git a/mm/page_alloc.c b/mm/page_alloc.c index ae96dd8..7c219eb 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3350,6 +3350,21 @@ 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); --------------000202020007030807040908-- -- 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