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

Alex Elder
2010-09-14T18:47:56Z

On Tue, 2010-09-14 at 20:56 +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.

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@sgi.com>

> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> ---
> 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

. . .