From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <464F3CCF.2070901@cosmosbay.com> Date: Sat, 19 May 2007 20:07:11 +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> In-Reply-To: <20070519013724.3d4b74e0.akpm@linux-foundation.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton , David Howells Cc: "linux-mm@kvack.org" , linux kernel , David Miller List-ID: Andrew Morton a ecrit : > On Fri, 18 May 2007 11:54:54 +0200 Eric Dumazet wrote: > >> 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. > > Watch the 200-column text, please. > >> 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); >> > > It went BUG. > > static inline int put_page_testzero(struct page *page) > { > VM_BUG_ON(atomic_read(&page->_count) == 0); > return atomic_dec_and_test(&page->_count); > } > > http://userweb.kernel.org/~akpm/s5000523.jpg > http://userweb.kernel.org/~akpm/config-vmm.txt I see :( Maybe David has an idea how this can be done properly ? ref : http://marc.info/?l=linux-netdev&m=117706074825048&w=2 -- 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