From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-f177.google.com (mail-ig0-f177.google.com [209.85.213.177]) by kanga.kvack.org (Postfix) with ESMTP id DCC9E6B0009 for ; Thu, 11 Feb 2016 08:53:05 -0500 (EST) Received: by mail-ig0-f177.google.com with SMTP id y8so5839996igp.1 for ; Thu, 11 Feb 2016 05:53:05 -0800 (PST) Received: from mx2.parallels.com (mx2.parallels.com. [199.115.105.18]) by mx.google.com with ESMTPS id rh6si38045739igc.2.2016.02.11.05.53.04 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 11 Feb 2016 05:53:05 -0800 (PST) Subject: Re: [RFC PATCH 3/3] mm: increase scalability of global memory commitment accounting References: <1455115941-8261-1-git-send-email-aryabinin@virtuozzo.com> <1455115941-8261-3-git-send-email-aryabinin@virtuozzo.com> <1455127253.715.36.camel@schen9-desk2.jf.intel.com> <20160210132818.589451dbb5eafae3fdb4a7ec@linux-foundation.org> <1455150256.715.60.camel@schen9-desk2.jf.intel.com> From: Andrey Ryabinin Message-ID: <56BC9281.6090505@virtuozzo.com> Date: Thu, 11 Feb 2016 16:54:09 +0300 MIME-Version: 1.0 In-Reply-To: <1455150256.715.60.camel@schen9-desk2.jf.intel.com> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Tim Chen , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andi Kleen , Mel Gorman , Vladimir Davydov , Konstantin Khlebnikov On 02/11/2016 03:24 AM, Tim Chen wrote: > On Wed, 2016-02-10 at 13:28 -0800, Andrew Morton wrote: > >> >> If a process is unmapping 4MB then it's pretty crazy for us to be >> hitting the percpu_counter 32 separate times for that single operation. >> >> Is there some way in which we can batch up the modifications within the >> caller and update the counter less frequently? Perhaps even in a >> single hit? > > I think the problem is the batch size is too small and we overflow > the local counter into the global counter for 4M allocations. > The reason for the small batch size was because we use > percpu_counter_read_positive in __vm_enough_memory and it is not precise > and the error could grow with large batch size. > > Let's switch to the precise __percpu_counter_compare that is > unaffected by batch size. It will do precise comparison and only add up > the local per cpu counters when the global count is not precise > enough. > I'm not certain about this. for_each_online_cpu() under spinlock somewhat doubtful. And if we are close to limit we will be hitting slowpath all the time. > So maybe something like the following patch with a relaxed batch size. > I have not tested this patch much other than compiling and booting > the kernel. I wonder if this works for Andrey. We could relax the batch > size further, but that will mean that we will incur the overhead > of summing the per cpu counters earlier when the global count get close > to the allowed limit. > > Thanks. > > Tim > -- 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