From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lb0-f182.google.com (mail-lb0-f182.google.com [209.85.217.182]) by kanga.kvack.org (Postfix) with ESMTP id F2CFF6B0032 for ; Thu, 8 Jan 2015 07:16:37 -0500 (EST) Received: by mail-lb0-f182.google.com with SMTP id u10so2496927lbd.13 for ; Thu, 08 Jan 2015 04:16:37 -0800 (PST) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id qp3si7765677lbb.81.2015.01.08.04.10.47 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 08 Jan 2015 04:10:47 -0800 (PST) Message-ID: <54AE73C5.4000409@suse.cz> Date: Thu, 08 Jan 2015 13:10:45 +0100 From: Vlastimil Babka MIME-Version: 1.0 Subject: Re: Dirty pages underflow on 3.14.23 References: <20150106150250.GA26895@phnom.home.cmpxchg.org> <20150107212858.GA6664@hostway.ca> <54ADA99A.90501@suse.cz> <20150108010426.GB6664@hostway.ca> In-Reply-To: <20150108010426.GB6664@hostway.ca> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Simon Kirby Cc: Holger Hoffst?tte , linux-mm@kvack.org, linux-kernel@vger.kernel.org On 01/08/2015 02:04 AM, Simon Kirby wrote: > On Wed, Jan 07, 2015 at 10:48:10PM +0100, Vlastimil Babka wrote: > >> On 01/07/2015 10:28 PM, Simon Kirby wrote: >> >> > Hmm...A possibly-related issue...Before trying this, after a fresh boot, >> > /proc/vmstat showed: >> > >> > nr_alloc_batch 4294541205 >> >> This can happen, and not be a problem in general. However, there was a fix >> abe5f972912d086c080be4bde67750630b6fb38b in 3.17 for a potential performance >> issue if this counter overflows on single processor configuration. It was marked >> stable, but the 3.16 series was discontinued before the fix could be backported. >> So if you are on single-core, you might hit the performance issue. > > That particular commit seems to just change the code path in that case, > but should it be underflowing at all on UP? Yes, the code using this counter is either treating it as signed, or includes a <0 tests. It's just the /proc output might be confusing here... >> > Still, nr_alloc_batch reads as 4294254379 after MySQL restart, and now >> > seems to stay up there. >> >> Hm if it stays there, then you are probably hitting the performance issue. Look >> at /proc/zoneinfo, which zone has the underflow. It means this zone will get >> unfair amount of allocations, while others may contain stale data and would be >> better candidates. > > In this case, it has only 640MB, and there's only DMA and Normal. This is > affecting Normal, and DMA is so small that it probably doesn't matter. > > Simon- > > -- > 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 > -- 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