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Re: [PATCH 01/18] xfs: single thread inode cache shrinking.

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH 01/18] xfs: single thread inode cache shrinking.
From: Alex Elder <aelder@xxxxxxx>
Date: Tue, 14 Sep 2010 13:48:26 -0500
Cc: xfs@xxxxxxxxxxx
In-reply-to: <1284461777-1496-2-git-send-email-david@xxxxxxxxxxxxx>
References: <1284461777-1496-1-git-send-email-david@xxxxxxxxxxxxx> <1284461777-1496-2-git-send-email-david@xxxxxxxxxxxxx>
Reply-to: aelder@xxxxxxx
On Tue, 2010-09-14 at 20:56 +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
> 
> 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.

This is an aside, but...

Shrinking still hits the first AG's more than the rest,
right?  I.e. if AG 0 has nr_to_scan reclaimable inodes, no
other AG's get their inodes reclaimed?

Anyway, this change looks good.

Reviewed-by: Alex Elder <aelder@xxxxxxx>

> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> ---
>  fs/xfs/linux-2.6/xfs_sync.c |   21 +++++++++++++++++++--
>  fs/xfs/xfs_mount.h          |    2 ++
>  2 files changed, 21 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/linux-2.6/xfs_sync.c b/fs/xfs/linux-2.6/xfs_sync.c
> index d59c4a6..bc54cd6 100644

. . .


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