From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pb0-f43.google.com (mail-pb0-f43.google.com [209.85.160.43]) by kanga.kvack.org (Postfix) with ESMTP id E6A536B00DD for ; Fri, 25 Oct 2013 19:32:35 -0400 (EDT) Received: by mail-pb0-f43.google.com with SMTP id md12so4760573pbc.2 for ; Fri, 25 Oct 2013 16:32:35 -0700 (PDT) Received: from psmtp.com ([74.125.245.137]) by mx.google.com with SMTP id ei3si5398912pbc.350.2013.10.25.16.32.34 for ; Fri, 25 Oct 2013 16:32:35 -0700 (PDT) Date: Sat, 26 Oct 2013 00:32:25 +0100 From: Fengguang Wu Subject: Re: Disabling in-memory write cache for x86-64 in Linux II Message-ID: <20131025233225.GA32051@localhost> References: <160824051.3072.1382685914055.JavaMail.mail@webmail07> <154617470.12445.1382725583671.JavaMail.mail@webmail11> <1999200.Zdacx0scmY@diego-arch> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1999200.Zdacx0scmY@diego-arch> Sender: owner-linux-mm@kvack.org List-ID: To: Diego Calleja Cc: "Artem S. Tashkinov" , david@lang.hm, neilb@suse.de, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, linux-fsdevel@vger.kernel.org, axboe@kernel.dk, linux-mm@kvack.org On Fri, Oct 25, 2013 at 09:40:13PM +0200, Diego Calleja wrote: > El Viernes, 25 de octubre de 2013 18:26:23 Artem S. Tashkinov escribiA3: > > Oct 25, 2013 05:26:45 PM, david wrote: > > >actually, I think the problem is more the impact of the huge write later > > >on. > > Exactly. And not being able to use applications which show you IO > > performance like Midnight Commander. You might prefer to use "cp -a" but I > > cannot imagine my life without being able to see the progress of a copying > > operation. With the current dirty cache there's no way to understand how > > you storage media actually behaves. > > > This is a problem I also have been suffering for a long time. It's not so much > how much and when the systems syncs dirty data, but how unreponsive the > desktop becomes when it happens (usually, with rsync + large files). Most > programs become completely unreponsive, specially if they have a large memory > consumption (ie. the browser). I need to pause rsync and wait until the > systems writes out all dirty data if I want to do simple things like scrolling > or do any action that uses I/O, otherwise I need to wait minutes. That's a problem. And it's kind of independent of the dirty threshold -- if you are doing large file copies in the background, it will lead to continuous disk writes and stalls anyway -- the large dirty threshold merely delays the write IO time. > I have 16 GB of RAM and excluding the browser (which usually uses about half > of a GB) and KDE itself, there are no memory hogs, so it seem like it's > something that shouldn't happen. I can understand that I/O operations are > laggy when there is some other intensive I/O ongoing, but right now the system > becomes completely unreponsive. If I am unlucky and Konsole also becomes > unreponsive, I need to switch to a VT (which also takes time). > > I haven't reported it before in part because I didn't know how to do it, "my > browser stalls" is not a very useful description and I didn't know what kind > of data I'm supposed to report. What's the kernel you are running? And it's writing to a hard disk? The stalls are most likely caused by either one of 1) write IO starves read IO 2) direct page reclaim blocked when - trying to writeout PG_dirty pages - trying to lock PG_writeback pages Which may be confirmed by running ps -eo ppid,pid,user,stat,pcpu,comm,wchan:32 or echo w > /proc/sysrq-trigger # and check dmesg during the stalls. The latter command works more reliably. Thanks, Fengguang -- 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