From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx137.postini.com [74.125.245.137]) by kanga.kvack.org (Postfix) with SMTP id B95436B00FD for ; Tue, 21 Feb 2012 19:34:41 -0500 (EST) Message-ID: <4F443814.6050209@fb.com> Date: Tue, 21 Feb 2012 16:34:28 -0800 From: Arun Sharma MIME-Version: 1.0 Subject: Re: [PATCH] mm: Enable MAP_UNINITIALIZED for archs with mmu References: <1326912662-18805-1-git-send-email-asharma@fb.com> <20120119114206.653b88bd.kamezawa.hiroyu@jp.fujitsu.com> <4F1E013E.9060009@fb.com> <20120124120704.3f09b206.kamezawa.hiroyu@jp.fujitsu.com> <4F1F5EB8.3000407@fb.com> In-Reply-To: <4F1F5EB8.3000407@fb.com> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: KAMEZAWA Hiroyuki Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Balbir Singh , akpm@linux-foundation.org On 1/24/12 5:45 PM, Arun Sharma wrote: > On 1/23/12 7:07 PM, KAMEZAWA Hiroyuki wrote: > >> You can see reduction of clear_page() cost by removing GFP_ZERO but >> what's your application's total performance ? Is it good enough >> considering >> many risks ? > > I see 90k calls/sec to clear_page_c when running our application. I > don't have data on the impact of GFP_ZERO alone, but an earlier > experiment when we tuned malloc to not call madvise(MADV_DONTNEED) > aggressively saved us 3% CPU. So I'm expecting this to be a 1-2% win. I saw some additional measurement data today. We were running at a lower-than-default value for the rate at which our malloc implementation releases unused faulted-in memory to the kernel via madvise(). This was done just to reduce the impact of clear_page() on application performance. But it cost us at least several hundred megs (if not more) in additional RSS. We compared the impact of increasing the madvise rate to the default[1]. This used to cause a 3% CPU regression earlier. But with the patch, the regression was completely gone and we recovered a bunch of memory in terms of reduced RSS. Hope this additional data is useful. Happy to clean up the patch and implement the opt-in flags. -Arun [1] The default rate is 32:1, i.e. no more than 1/32th of the heap is unused and dirty (i.e. contributing to RSS). -- 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