From: Christoph Hellwig <hch@infradead.org>
To: Dave Chinner <david@fromorbit.com>
Cc: xfs@oss.sgi.com
Subject: Re: [PATCH] xfs: single thread inode cache shrinking.
Date: Wed, 8 Sep 2010 23:00:57 -0400 [thread overview]
Message-ID: <20100909030057.GA32472@infradead.org> (raw)
In-Reply-To: <1283959243-29176-1-git-send-email-david@fromorbit.com>
On Thu, Sep 09, 2010 at 01:20:43AM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> Having multiple CPUs trying to do the same cache shrinking work can
> be actively harmful to perforamnce when the shrinkers land in the
> same AGs. They then lockstep on perag locks, causing contention and
> slowing each other down. Reclaim walking is sufficiently efficient
> that we do no need parallelism to make significant progress, so stop
> parallel access at the door.
>
> Instead, keep track of the number of objects the shrinkers want
> cleaned and make sure the single running shrinker does not stop
> until it has hit the threshold that the other shrinker calls have
> built up.
>
> This increases the cold-cache unlink rate of a 8-way parallel unlink
> workload from about 15,000 unlinks/s to 60-70,000 unlinks/s for the
> same CPU usage (~700%), resulting in the runtime for a 200M inode
> unlink workload dropping from 4h50m to just under 1 hour.
The code looks good, but long term I think this needs to be fixed
in the caller, not in every shrinker instance.
Reviewed-by: Christoph Hellwig <hch@lst.de>
> + nr_to_scan += atomic64_read(&mp->m_ino_shrink_nr);
> + atomic64_set(&mp->m_ino_shrink_nr, 0);
To be totally race free this should use atomic64_cmpxchg.
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next prev parent reply other threads:[~2010-09-09 3:00 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-08 15:20 [PATCH] xfs: single thread inode cache shrinking Dave Chinner
2010-09-09 3:00 ` Christoph Hellwig [this message]
2010-09-10 3:29 ` Dave Chinner
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