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Re: [PATCH 3/9] xfs: convert ENOSPC inode flushing to use new syncd work

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH 3/9] xfs: convert ENOSPC inode flushing to use new syncd workqueue
From: Alex Elder <aelder@xxxxxxx>
Date: Thu, 07 Apr 2011 16:16:11 -0500
Cc: xfs@xxxxxxxxxxx
In-reply-to: <1302141445-27457-4-git-send-email-david@xxxxxxxxxxxxx>
References: <1302141445-27457-1-git-send-email-david@xxxxxxxxxxxxx> <1302141445-27457-4-git-send-email-david@xxxxxxxxxxxxx>
Reply-to: aelder@xxxxxxx
On Thu, 2011-04-07 at 11:57 +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
> 
> On of the problems with the current inode flush at ENOSPC is that we
> queue a flush per ENOSPC event, regardless of how many are already
> queued. Thi can result in    hundreds of queued flushes, most of
> which simply burn CPU scanned and do no real work. This simply slows
> down allocation at ENOSPC.
> 
> We really only need one active flush at a time, and we can easily
> implement that via the new xfs_syncd_wq. All we need to do is queue
> a flush if one is not already active, then block waiting for the
> currently active flush to complete. The result is that we only ever
> have a single ENOSPC inode flush active at a time and this greatly
> reduces the overhead of ENOSPC processing.
> 
> On my 2p test machine, this results in tests exercising ENOSPC
> conditions running significantly faster - 042 halves execution time,
> 083 drops from 60s to 5s, etc - while not introducing test
> regressions.
> 
> This allows us to remove the old xfssyncd threads and infrastructure
> as they are no longer used.

Looks good.  You got rid of a useless log force as well.

Reviewed-by: Alex Elder <aelder@xxxxxxx>

> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>


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