From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pb0-f49.google.com (mail-pb0-f49.google.com [209.85.160.49]) by kanga.kvack.org (Postfix) with ESMTP id 6306E6B0035 for ; Fri, 1 Nov 2013 17:11:37 -0400 (EDT) Received: by mail-pb0-f49.google.com with SMTP id xb4so4746047pbc.8 for ; Fri, 01 Nov 2013 14:11:37 -0700 (PDT) Received: from psmtp.com ([74.125.245.197]) by mx.google.com with SMTP id y7si5417203pbi.203.2013.11.01.14.11.35 for ; Fri, 01 Nov 2013 14:11:36 -0700 (PDT) Message-ID: <1383340291.2653.33.camel@buesod1.americas.hpqcorp.net> Subject: Re: [PATCH] mm: cache largest vma From: Davidlohr Bueso Date: Fri, 01 Nov 2013 14:11:31 -0700 In-Reply-To: <5274114B.7010302@gmail.com> References: <1383337039.2653.18.camel@buesod1.americas.hpqcorp.net> <5274114B.7010302@gmail.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: KOSAKI Motohiro Cc: Andrew Morton , Hugh Dickins , Michel Lespinasse , Ingo Molnar , Mel Gorman , Rik van Riel , Guan Xuetao , aswin@hp.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org On Fri, 2013-11-01 at 16:38 -0400, KOSAKI Motohiro wrote: > (11/1/13 4:17 PM), Davidlohr Bueso wrote: > > While caching the last used vma already does a nice job avoiding > > having to iterate the rbtree in find_vma, we can improve. After > > studying the hit rate on a load of workloads and environments, > > it was seen that it was around 45-50% - constant for a standard > > desktop system (gnome3 + evolution + firefox + a few xterms), > > and multiple java related workloads (including Hadoop/terasort), > > and aim7, which indicates it's better than the 35% value documented > > in the code. > > > > By also caching the largest vma, that is, the one that contains > > most addresses, there is a steady 10-15% hit rate gain, putting > > it above the 60% region. This improvement comes at a very low > > overhead for a miss. Furthermore, systems with !CONFIG_MMU keep > > the current logic. > > I'm slightly surprised this cache makes 15% hit. Which application > get a benefit? You listed a lot of applications, but I'm not sure > which is highly depending on largest vma. Well I chose the largest vma because it gives us a greater chance of being already cached when we do the lookup for the faulted address. The 15% improvement was with Hadoop. According to my notes it was at ~48% with the baseline kernel and increased to ~63% with this patch. In any case I didn't measure the rates on a per-task granularity, but at a general system level. When a system is first booted I can see that the mmap_cache access rate becomes the determinant factor and when adding a workload it doesn't change much. One exception to this was a kernel build, where we go from ~50% to ~89% hit rate on a vanilla kernel. Thanks, Davidlohr -- 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