Re: [PATCH 00/45] some writeback experiments
From: Wu Fengguang
Date: Thu Oct 08 2009 - 01:46:15 EST
On Thu, Oct 08, 2009 at 01:33:35PM +0800, Wu Fengguang wrote:
> 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..
Just switched to 512k wsize, and things improved: in most time the 8
nfsd are not all blocked. However, the bumpiness still remains:
nr_writeback nr_dirty nr_unstable
11105 58080 15042
11105 58080 15042
11233 54583 18626
11101 51964 22036
11105 51978 22065
11233 52362 22577
10985 58538 13500
11233 53748 19721
11047 51999 21778
11105 50262 23572
11105 50262 20441
10985 52772 20721
10977 52109 21516
11105 48296 26629
11105 48296 26629
10985 52191 21042
11166 51456 22296
10980 50681 24466
11233 45352 30488
11233 45352 30488
11105 45475 30616
11131 45313 20355
11233 51126 22637
11233 51126 22637
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 S< svc_recv nfsd
4691 4691 TS - -5 24 0 0.1 S< svc_recv nfsd
4692 4692 TS - -5 24 0 0.1 R< ? nfsd
4693 4693 TS - -5 24 0 0.1 S< svc_recv nfsd
4694 4694 TS - -5 24 0 0.1 S< svc_recv nfsd
4695 4695 TS - -5 24 0 0.1 S< svc_recv nfsd
4696 4696 TS - -5 24 0 0.1 S< svc_recv nfsd
4697 4697 TS - -5 24 0 0.1 R< ? 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 S< svc_recv nfsd
4692 4692 TS - -5 24 1 0.1 D< log_wait_commit nfsd
4693 4693 TS - -5 24 0 0.1 D< generic_file_aio_write nfsd
4694 4694 TS - -5 24 0 0.1 S< svc_recv 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 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 S< svc_recv nfsd
4691 4691 TS - -5 24 0 0.1 S< svc_recv nfsd
4692 4692 TS - -5 24 1 0.1 R< ? nfsd
4693 4693 TS - -5 24 1 0.1 R< ? nfsd
4694 4694 TS - -5 24 1 0.1 R< ? nfsd
4695 4695 TS - -5 24 1 0.1 S< svc_recv nfsd
4696 4696 TS - -5 24 0 0.1 S< svc_recv nfsd
4697 4697 TS - -5 24 1 0.1 S< svc_recv 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< generic_file_aio_write nfsd
4691 4691 TS - -5 24 0 0.1 S< svc_recv nfsd
4692 4692 TS - -5 24 1 0.1 D< nfsd_sync nfsd
4693 4693 TS - -5 24 1 0.1 D< sync_buffer nfsd
4694 4694 TS - -5 24 1 0.1 D< generic_file_aio_write nfsd
4695 4695 TS - -5 24 1 0.1 S< svc_recv 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
Thanks,
Fengguang
> 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
> > > >
> > > > --
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