Re: [PATCH 02/28] xfs: Throttle commits on delayed background CIL push

[Darrick J. Wong]

On Sat, Nov 02, 2019 at 08:40:40AM +1100, Dave Chinner wrote:
> On Fri, Nov 01, 2019 at 08:04:26AM -0400, Brian Foster wrote:
> > On Fri, Nov 01, 2019 at 10:45:52AM +1100, Dave Chinner wrote:
> > > From: Dave Chinner <dchinner@xxxxxxxxxx>
> > > 
> > > In certain situations the background CIL push can be indefinitely
> > > delayed. While we have workarounds from the obvious cases now, it
> > > doesn't solve the underlying issue. This issue is that there is no
> > > upper limit on the CIL where we will either force or wait for
> > > a background push to start, hence allowing the CIL to grow without
> > > bound until it consumes all log space.
> > > 
> > > To fix this, add a new wait queue to the CIL which allows background
> > > pushes to wait for the CIL context to be switched out. This happens
> > > when the push starts, so it will allow us to block incoming
> > > transaction commit completion until the push has started. This will
> > > only affect processes that are running modifications, and only when
> > > the CIL threshold has been significantly overrun.
> > > 
> > > This has no apparent impact on performance, and doesn't even trigger
> > > until over 45 million inodes had been created in a 16-way fsmark
> > > test on a 2GB log. That was limiting at 64MB of log space used, so
> > > the active CIL size is only about 3% of the total log in that case.
> > > The concurrent removal of those files did not trigger the background
> > > sleep at all.
> > > 
> > > Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> > > Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
> > > ---
> > 
> > I don't recall posting an R-b tag for this one...
> 
> Argh, sorry. I must have screwed up transcribing them from the
> mailing list.
> 
> > That said, I think my only outstanding feedback (side discussion aside)
> > was the code factoring in xlog_cil_push_background().
> 
> I'll go back and look at that, 'cause clearly I was looking at the
> wrong patch when I screwed up the rvb tag...

I'll keep an eye on the list for a revised series.

--D

> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@xxxxxxxxxxxxx