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Date: Thu, 8 Oct 2009 13:33:35 +0800 From: Wu Fengguang <fengguang.wu@...el.com> To: Peter Staubach <staubach@...hat.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, Theodore Tso <tytso@....edu>, Christoph Hellwig <hch@...radead.org>, Dave Chinner <david@...morbit.com>, Chris Mason <chris.mason@...cle.com>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, "Li, Shaohua" <shaohua.li@...el.com>, Myklebust Trond <Trond.Myklebust@...app.com>, "jens.axboe@...cle.com" <jens.axboe@...cle.com>, Jan Kara <jack@...e.cz>, Nick Piggin <npiggin@...e.de>, "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 00/45] some writeback experiments On Wed, Oct 07, 2009 at 11:18:22PM +0800, Wu Fengguang wrote: > On Wed, Oct 07, 2009 at 09:47:14PM +0800, Peter Staubach wrote: > > > > > # vmmon -d 1 nr_writeback nr_dirty nr_unstable # (per 1-second samples) > > > nr_writeback nr_dirty nr_unstable > > > 11227 41463 38044 > > > 11227 41463 38044 > > > 11227 41463 38044 > > > 11227 41463 38044 > > I guess in the above 4 seconds, either client or (more likely) server > is blocked. A blocked server cannot send ACKs to knock down both Yeah the server side is blocked. The nfsd are mostly blocked in generic_file_aio_write(), in particular, the i_mutex lock! I'm copying one or two big files over NFS, so the i_mutex lock is heavily contented. I'm using the default wsize=4096 for NFS-root.. wfg ~% ps -o pid,tid,class,rtprio,ni,pri,psr,pcpu,stat,wchan:24,comm ax|g nfs 329 329 TS - -5 24 1 0.0 S< worker_thread nfsiod 4690 4690 TS - -5 24 0 0.1 D< generic_file_aio_write nfsd 4691 4691 TS - -5 24 0 0.0 D< generic_file_aio_write nfsd 4692 4692 TS - -5 24 0 0.0 D< generic_file_aio_write nfsd 4693 4693 TS - -5 24 0 0.0 D< generic_file_aio_write nfsd 4694 4694 TS - -5 24 0 0.1 D< generic_file_aio_write nfsd 4695 4695 TS - -5 24 1 0.1 D< generic_file_aio_write nfsd 4696 4696 TS - -5 24 1 0.0 D< log_wait_commit nfsd 4697 4697 TS - -5 24 0 0.0 D< generic_file_aio_write nfsd wfg ~% ps -o pid,tid,class,rtprio,ni,pri,psr,pcpu,stat,wchan:24,comm ax|g nfs 329 329 TS - -5 24 1 0.0 S< worker_thread nfsiod 4690 4690 TS - -5 24 0 0.1 D< generic_file_aio_write nfsd 4691 4691 TS - -5 24 0 0.0 D< generic_file_aio_write nfsd 4692 4692 TS - -5 24 0 0.0 D< generic_file_aio_write nfsd 4693 4693 TS - -5 24 0 0.0 D< sync_buffer nfsd 4694 4694 TS - -5 24 0 0.1 D< generic_file_aio_write nfsd 4695 4695 TS - -5 24 1 0.1 D< generic_file_aio_write nfsd 4696 4696 TS - -5 24 1 0.0 D< generic_file_aio_write nfsd 4697 4697 TS - -5 24 0 0.0 D< generic_file_aio_write nfsd wfg ~% ps -o pid,tid,class,rtprio,ni,pri,psr,pcpu,stat,wchan:24,comm ax|g nfs 329 329 TS - -5 24 1 0.0 S< worker_thread nfsiod 4690 4690 TS - -5 24 0 0.1 D< generic_file_aio_write nfsd 4691 4691 TS - -5 24 0 0.1 D< get_request_wait nfsd 4692 4692 TS - -5 24 0 0.1 D< generic_file_aio_write nfsd 4693 4693 TS - -5 24 0 0.1 S< svc_recv nfsd 4694 4694 TS - -5 24 0 0.1 D< generic_file_aio_write nfsd 4695 4695 TS - -5 24 0 0.1 D< generic_file_aio_write nfsd 4696 4696 TS - -5 24 0 0.1 S< svc_recv nfsd 4697 4697 TS - -5 24 1 0.1 D< generic_file_aio_write nfsd wfg ~% ps -o pid,tid,class,rtprio,ni,pri,psr,pcpu,stat,wchan:24,comm ax|g nfs 329 329 TS - -5 24 1 0.0 S< worker_thread nfsiod 4690 4690 TS - -5 24 1 0.1 D< get_write_access nfsd 4691 4691 TS - -5 24 0 0.1 D< generic_file_aio_write nfsd 4692 4692 TS - -5 24 0 0.1 D< generic_file_aio_write nfsd 4693 4693 TS - -5 24 1 0.1 D< generic_file_aio_write nfsd 4694 4694 TS - -5 24 1 0.1 D< get_write_access nfsd 4695 4695 TS - -5 24 0 0.1 D< generic_file_aio_write nfsd 4696 4696 TS - -5 24 0 0.1 D< generic_file_aio_write nfsd 4697 4697 TS - -5 24 0 0.1 D< generic_file_aio_write nfsd Thanks, Fengguang > nr_writeback/nr_unstable. And the stuck nr_writeback will freeze > nr_dirty as well, because the dirtying process is throttled until > it receives enough "PG_writeback cleared" event, however the bdi-flush > thread is also blocked when trying to clear more PG_writeback, because > the client side nr_writeback limit has been reached. In summary, > > server blocked => nr_writeback stuck => nr_writeback limit reached > => bdi-flush blocked => no end_page_writeback() => dirtier blocked > => nr_dirty stuck > > Thanks, > Fengguang > > > > 11045 53987 6490 > > > 11033 53120 8145 > > > 11195 52143 10886 > > > 11211 52144 10913 > > > 11211 52144 10913 > > > 11211 52144 10913 > > > > > > btrfs seems to maintain a private pool of writeback pages, which can go out of > > > control: > > > > > > nr_writeback nr_dirty > > > 261075 132 > > > 252891 195 > > > 244795 187 > > > 236851 187 > > > 228830 187 > > > 221040 218 > > > 212674 237 > > > 204981 237 > > > > > > XFS has very interesting "bumpy writeback" behavior: it tends to wait > > > collect enough pages and then write the whole world. > > > > > > nr_writeback nr_dirty > > > 80781 0 > > > 37117 37703 > > > 37117 43933 > > > 81044 6 > > > 81050 0 > > > 43943 10199 > > > 43930 36355 > > > 43930 36355 > > > 80293 0 > > > 80285 0 > > > 80285 0 > > > > > > Thanks, > > > Fengguang > > > > > > -- > > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > > > the body of a message to majordomo@...r.kernel.org > > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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