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Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME inodes

From Eryu Guan <eguan@redhat.com>
Newsgroups linux.kernel
Subject Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME inodes
Date 2015-08-20 08:20 +0200
Message-ID <pZrmG-4VL-19@gated-at.bofh.it> (permalink)
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On Wed, Aug 19, 2015 at 07:56:11AM +1000, Dave Chinner wrote:
> On Tue, Aug 18, 2015 at 12:54:39PM -0700, Tejun Heo wrote:
> > Hello,
> > 
> > On Tue, Aug 18, 2015 at 10:47:18AM -0700, Tejun Heo wrote:
> > > Hmm... the only possibility I can think of is tot_write_bandwidth
> > > being zero when it shouldn't be.  I've been staring at the code for a
> > > while now but nothing rings a bell.  Time for another debug patch, I
> > > guess.
> > 
> > So, I can now reproduce the bug (it takes a lot of trials but lowering
> > the number of tested files helps quite a bit) and instrumented all the
> > early exit paths w/o the fix patch.  bdi_has_dirty_io() and
> > wb_has_dirty_io() are never out of sync with the actual dirty / io
> > lists even when the test 048 fails, so the bug at least is not caused
> > by writeback skipping due to buggy bdi/wb_has_dirty_io() result.
> > Whenever it skips, all the lists are actually empty (verified while
> > holding list_lock).
> > 
> > One suspicion I have is that this could be a subtle timing issue which
> > is being exposed by the new short-cut path.  Anything which adds delay
> > seems to make the issue go away.  Dave, does anything ring a bell?
> 
> No, it doesn't. The data writeback mechanisms XFS uses are all
> generic. It marks inodes I_DIRTY_PAGES and lets the generic code
> take care of everything else. Yes, we do delayed allocation during
> writeback, and we log the inode size updates during IO completion,
> so if inode sizes are not getting updated, then Occam's Razor
> suggests that writeback is not happening.
> 
> I'd suggest looking at some of the XFS tracepoints during the test:
> 
> tracepoint			trigger
> xfs_file_buffered_write		once per write syscall
> xfs_file_sync			once per fsync per inode
> xfs_vm_writepage		every ->writepage call
> xfs_setfilesize			every IO completion that updates inode size

I gave the tracepoints a try, but my root fs is xfs so I got many
noises. I'll try to install a new vm with ext4 as root fs. But I'm not
sure if the new vm could reproduce the failure, will see.

BTW, I guess xfs_vm_writepage should be xfs_writepage, and xfs_file_sync
should be xfs_file_fsync?

Thanks,
Eryu
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[PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME inodes Tejun Heo <tj@kernel.org> - 2015-08-14 00:50 +0200
  Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Jan Kara <jack@suse.cz> - 2015-08-14 13:20 +0200
    Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Damien Wyart <damien.wyart@gmail.com> - 2015-08-14 17:30 +0200
      Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Tejun Heo <tj@kernel.org> - 2015-08-17 22:10 +0200
        Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Damien Wyart <damien.wyart@gmail.com> - 2015-08-18 07:40 +0200
    Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Tejun Heo <tj@kernel.org> - 2015-08-17 22:10 +0200
      Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Jan Kara <jack@suse.cz> - 2015-08-18 11:20 +0200
        Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Tejun Heo <tj@kernel.org> - 2015-08-18 19:50 +0200
          Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Tejun Heo <tj@kernel.org> - 2015-08-18 22:00 +0200
            Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Dave Chinner <david@fromorbit.com> - 2015-08-19 00:00 +0200
              Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Eryu Guan <eguan@redhat.com> - 2015-08-20 08:20 +0200
                Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Tejun Heo <tj@kernel.org> - 2015-08-20 19:00 +0200
                Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Dave Chinner <david@fromorbit.com> - 2015-08-21 01:10 +0200
                Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Tejun Heo <tj@kernel.org> - 2015-08-24 20:20 +0200
                Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Dave Chinner <david@fromorbit.com> - 2015-08-25 00:30 +0200
                Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Tejun Heo <tj@kernel.org> - 2015-08-25 01:00 +0200
              Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Eryu Guan <eguan@redhat.com> - 2015-08-21 12:30 +0200
                Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Dave Chinner <david@fromorbit.com> - 2015-08-22 02:40 +0200
                Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Eryu Guan <eguan@redhat.com> - 2015-08-22 06:50 +0200
                Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Dave Chinner <david@fromorbit.com> - 2015-08-24 03:20 +0200
                Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Eryu Guan <eguan@redhat.com> - 2015-08-24 05:20 +0200
                Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Dave Chinner <david@fromorbit.com> - 2015-08-24 08:30 +0200
                Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Eryu Guan <eguan@redhat.com> - 2015-08-24 10:40 +0200
                Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Dave Chinner <david@fromorbit.com> - 2015-08-24 11:00 +0200
                Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Jan Kara <jack@suse.cz> - 2015-08-24 11:30 +0200
                Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Tejun Heo <tj@kernel.org> - 2015-08-24 17:00 +0200
                Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Tejun Heo <tj@kernel.org> - 2015-08-24 19:20 +0200
                Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Jan Kara <jack@suse.cz> - 2015-08-24 21:10 +0200
                Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Tejun Heo <tj@kernel.org> - 2015-08-24 21:40 +0200
                Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Jan Kara <jack@suse.cz> - 2015-08-24 23:10 +0200
                Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Tejun Heo <tj@kernel.org> - 2015-08-24 23:50 +0200
                Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Dave Chinner <david@fromorbit.com> - 2015-08-25 01:00 +0200
                Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME  inodes Tejun Heo <tj@kernel.org> - 2015-08-25 01:00 +0200
  [PATCH v2 block/for-linus] writeback: sync_inodes_sb() must write  out I_DIRTY_TIME inodes and always call wait_sb_inodes() Tejun Heo <tj@kernel.org> - 2015-08-25 20:20 +0200
    Re: [PATCH v2 block/for-linus] writeback: sync_inodes_sb() must write  out I_DIRTY_TIME inodes and always call wait_sb_inodes() Jens Axboe <axboe@kernel.dk> - 2015-08-25 22:40 +0200
    Re: [PATCH v2 block/for-linus] writeback: sync_inodes_sb() must  write out I_DIRTY_TIME inodes and always call wait_sb_inodes() Jan Kara <jack@suse.cz> - 2015-08-26 11:10 +0200

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