From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id 135FD8D0040 for ; Tue, 29 Mar 2011 21:01:24 -0400 (EDT) Subject: Re: [PATCH]mmap: add alignment for some variables From: Shaohua Li In-Reply-To: <20110329152434.d662706f.akpm@linux-foundation.org> References: <1301277536.3981.27.camel@sli10-conroe> <1301360054.3981.31.camel@sli10-conroe> <20110329152434.d662706f.akpm@linux-foundation.org> Content-Type: text/plain; charset="UTF-8" Date: Wed, 30 Mar 2011 09:01:22 +0800 Message-ID: <1301446882.3981.33.camel@sli10-conroe> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Andi Kleen , linux-mm , lkml , Rik van Riel , Hugh Dickins On Wed, 2011-03-30 at 06:24 +0800, Andrew Morton wrote: > On Tue, 29 Mar 2011 08:54:14 +0800 > Shaohua Li wrote: > > > -struct percpu_counter vm_committed_as; > > +struct percpu_counter vm_committed_as ____cacheline_internodealigned_in_smp; > > Why ____cacheline_internodealigned_in_smp? That's pretty aggressive. > > afacit the main benefit from this will occur if the read-only > vm_committed_as.counters lands in the same cacheline as some > write-frequently storage. vm_committed_as can be frequently updated in some workloads too. > But that's a complete mad guess and I'd prefer not to have to guess. is below updated patch better to you? Make some variables have correct alignment/section to avoid cache issue. In a workload which heavily does mmap/munmap, the variables will be used frequently. Signed-off-by: Shaohua Li --- mm/mmap.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) Index: linux/mm/mmap.c =================================================================== --- linux.orig/mm/mmap.c 2011-03-30 08:45:05.000000000 +0800 +++ linux/mm/mmap.c 2011-03-30 08:59:23.000000000 +0800 @@ -84,10 +84,14 @@ pgprot_t vm_get_page_prot(unsigned long } EXPORT_SYMBOL(vm_get_page_prot); -int sysctl_overcommit_memory = OVERCOMMIT_GUESS; /* heuristic overcommit */ -int sysctl_overcommit_ratio = 50; /* default is 50% */ +int sysctl_overcommit_memory __read_mostly = OVERCOMMIT_GUESS; /* heuristic overcommit */ +int sysctl_overcommit_ratio __read_mostly = 50; /* default is 50% */ int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT; -struct percpu_counter vm_committed_as; +/* + * Make sure vm_committed_as in one cacheline and not cacheline shared with + * other variables. It can be updated by several CPUs frequently. + */ +struct percpu_counter vm_committed_as ____cacheline_internodealigned_in_smp; /* * Check that a process has enough memory to allocate a new virtual -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org