From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f49.google.com (mail-pa0-f49.google.com [209.85.220.49]) by kanga.kvack.org (Postfix) with ESMTP id 684CC6B0038 for ; Thu, 25 Jun 2015 20:57:41 -0400 (EDT) Received: by pactm7 with SMTP id tm7so58779487pac.2 for ; Thu, 25 Jun 2015 17:57:41 -0700 (PDT) Received: from mail-pd0-x22d.google.com (mail-pd0-x22d.google.com. [2607:f8b0:400e:c02::22d]) by mx.google.com with ESMTPS id iw5si18071356pbc.27.2015.06.25.17.57.40 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 25 Jun 2015 17:57:40 -0700 (PDT) Received: by pdbci14 with SMTP id ci14so63762753pdb.2 for ; Thu, 25 Jun 2015 17:57:39 -0700 (PDT) Date: Fri, 26 Jun 2015 09:58:08 +0900 From: Sergey Senozhatsky Subject: Re: extremely long blockages when doing random writes to SSD Message-ID: <20150626005808.GA5704@swordfish> References: <20150624152518.d3a5408f2bde405df1e6e5c4@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Luigi Semenzato Cc: Andrew Morton , Linux Memory Management List Hello, On (06/25/15 11:24), Luigi Semenzato wrote: > I looked at this some more and I am not sure that there is any bug, or > other possible tuning. > > While the random-write process runs, iostat -x -k 1 reports these numbers: > > average queue size: around 300 > average write wait: typically 200 to 400 ms, but can be over 1000 ms > average read wait: typically 50 to 100 ms > > (more info at crbug.com/414709) > > The read latency may be enough to explain the jank. In addition, the > browser can do fsyncs, and I think that those will block for a long > time. > > Ionice doesn't seem to make a difference. I suspect that once the > blocks are in the output queue, it's first-come/first-serve. Is this > correct or am I confused? > > We can fix this on the application side but only partially. The OS > version updater can use O_SYNC. The problem is that his can happen in > a number of situations, such as when simply downloading a large file, > and in other code we don't control. > do you use CONFIG_IOSCHED_DEADLINE or CONFIG_IOSCHED_CFQ? -ss -- 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