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Re: [PATCH 7/9] xfs: push the AIL from memory reclaim and periodic sync

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: [PATCH 7/9] xfs: push the AIL from memory reclaim and periodic sync
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Thu, 7 Apr 2011 10:15:48 +1000
Cc: xfs@xxxxxxxxxxx
In-reply-to: <20110406183356.GA23275@xxxxxxxxxxxxx>
References: <1302070758-17312-1-git-send-email-david@xxxxxxxxxxxxx> <1302070758-17312-8-git-send-email-david@xxxxxxxxxxxxx> <20110406183356.GA23275@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
On Wed, Apr 06, 2011 at 02:33:56PM -0400, Christoph Hellwig wrote:
> The patch looks correct, but I wonder what the performance implications
> of flushing the AIL every 30 seconds are.  Did you benchmark the
> patchset to see what it does to performance numbers for metadata
> intensive workloads?

In my measurements it's made no difference.

If the workload is being sustained for more than a few seconds, then
memory reclaim typically becomes active and the push from there
becomes the dominating factor. This effectively makes the syncd work
trigger a no-op.

If the push from the syncd work does trigger work to be done, it's
generally because the filesystem has gone to idle or only has a low
level of modifications being done. In either case, it doesn't affect
performance, especially with delaylog pinning the working set of
metadata in memory...

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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