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Re: [PATCH 35/36] repair: Increase default repair parallelism on large f

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH 35/36] repair: Increase default repair parallelism on large filesystems
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Wed, 13 Nov 2013 08:10:29 -0800
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1384324860-25677-36-git-send-email-david@xxxxxxxxxxxxx>
References: <1384324860-25677-1-git-send-email-david@xxxxxxxxxxxxx> <1384324860-25677-36-git-send-email-david@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Wed, Nov 13, 2013 at 05:40:59PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
> Large filesystems or high AG count filesystems generally have more
> inherent parallelism in the backing storage. We shoul dmake use of
> this by default to speed up repair times. Make xfs_repair use an
> "auto-stride" configuration on filesystems with enough AGs to be
> considered "multidisk" configurations.
> This difference in elaspsed time to repair a 100TB filesystem with
> 50 million inodes in it with all metadata in flash is:
>               Time    IOPS    BW      CPU     RAM
> vanilla:      2719s    2900    55MB/s  25%    0.95GB
> patched:       908s   varied  varied  varied  2.33GB
> With the patched kernel, there were IO peaks of over 1.3GB/s during
> AG scanning. Some phases now run at noticably different speeds
>       - phase 3 ran at ~180% CPU, 18,000 IOPS and 130MB/s,
>       - phase 4 ran at ~280% CPU, 12,000 IOPS and 100MB/s
>       - the other phases were similar to the vanilla repair.
> Memory usage is increased because of the increased buffer cache
> size as a result of concurrent AG scanning using it.

Looks good as long as you stick your promise to clean up the magic
numbers later.

Reviewed-by: Christoph Hellwig <hch@xxxxxx>

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