Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752411Ab0BHOIk (ORCPT ); Mon, 8 Feb 2010 09:08:40 -0500 Received: from 0122700014.0.fullrate.dk ([95.166.99.235]:40056 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752453Ab0BHOIi (ORCPT ); Mon, 8 Feb 2010 09:08:38 -0500 Date: Mon, 8 Feb 2010 15:08:37 +0100 From: Jens Axboe To: Jan Engelhardt Cc: Linux Kernel Mailing List Subject: Re: kswapd continuously active Message-ID: <20100208140837.GN1025@kernel.dk> References: <20100125130627.GO13771@kernel.dk> <20100205130002.GI1025@kernel.dk> <20100205131220.GK1025@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2439 Lines: 59 On Mon, Feb 08 2010, Jan Engelhardt wrote: > > On Sunday 2010-02-07 11:50, Jan Engelhardt wrote: > >On Friday 2010-02-05 14:24, Jan Engelhardt wrote: > >>>> The ext4 filesystem is already mounted with barrier=0. If there > >>>> is any block-level barriers I also can turn off, what would be > >>>> the command? > >>> > >>>barrier=0 is enough. I do wonder why your writeback rate is that slow, > >>>then. The disk has write back caching enabled? > >> > >>Yes, that seems to be the case at least. In fact the box is all fluffy > >>when nobody runs sync(1), which is what makes it so strange. > >> > >>sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't > >>support DPO or FUA > > > >Here is an alternate trace that just happened. > > > >INFO: task flush-8:0:343 blocked for more than 120 seconds. > >"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > >flush-8:0 D 0000000000555930 6664 343 2 0x18000000000 > >Call Trace: > > [00000000005555f4] start_this_handle+0x324/0x4b0 > > [0000000000555930] jbd2_journal_start+0x94/0xc0 > > [000000000052ddb8] ext4_da_writepages+0x1e0/0x460 > > [000000000049bf30] do_writepages+0x28/0x48 > > [00000000004e6d58] writeback_single_inode+0xf0/0x330 > > [00000000004e7b24] writeback_inodes_wb+0x4c8/0x5d8 > > [00000000004e7da4] wb_writeback+0x170/0x1ec > > [00000000004e8074] wb_do_writeback+0x188/0x1a4 > > [00000000004e80b8] bdi_writeback_task+0x28/0xa0 > > [00000000004a76c8] bdi_start_fn+0x64/0xc4 > > [0000000000475f84] kthread+0x58/0x6c > > [000000000042ade0] kernel_thread+0x30/0x48 > > [0000000000475ee0] kthreadd+0xb8/0x104 > > Could it be that there is something synchronize_rcu()-like in the > game that???? as a result of how RCU works???? just takes ages with 24 > VCPUs? The only synchronize_rcu() involved in the writeback code happens when a bdi exits, so you should not hit that. It'll do call_rcu() for work completions, but 1) you should not see a lot of work entries, and 2) lots of other kernel code will do that, too. Are you seeing a lot of CPU usage? What does eg perf top -a say? And what setup is this, I didn't realize you were running a virtualized setup? -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/