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From: Dave Chinner <david@fromorbit.com>
To: Josef Bacik <josef@toxicpanda.com>
Cc: linux-xfs@vger.kernel.org, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH V2 00/26] mm, xfs: non-blocking inode reclaim
Date: Sat, 12 Oct 2019 10:48:42 +1100
Message-ID: <20191011234842.GQ16973@dread.disaster.area> (raw)
In-Reply-To: <20191011190305.towurweq7gsah4vr@macbook-pro-91.dhcp.thefacebook.com>

On Fri, Oct 11, 2019 at 03:03:08PM -0400, Josef Bacik wrote:
> On Wed, Oct 09, 2019 at 02:20:58PM +1100, Dave Chinner wrote:
> > Hi folks,
> > 
> > This is the second version of the RFC I originally posted here:
> > 
> > https://lore.kernel.org/linux-xfs/20190801021752.4986-1-david@fromorbit.com/
> > 
> > The original description of the patchset is below, the issues and
> > approach to solving them has not changed. THere is some
> > restructuring of the patch set - the first few patches are all the
> > XFS fixes that can be merged regardless of the rest of the patchset,
> > but the non-blocking reclaim is somewhat dependent of them for
> > correct behaviour. The second set of patches are the shrinker
> > infrastructure changes needed for the shrinkers to feed back
> > reclaim progress to the main reclaim instructure and act on the
> > feedback. The last set of patches are the XFS changes needed to
> > convert inode reclaim over to a non-blocking, IO-less algorithm.
> 
> I looked through the MM patches and other than the congestion thing they look
> reasonable.  I think I can probably use this stuff to drop the use of the btree
> inode.  However I'm wondering if it would be a good idea to add an explicit
> backoff thing for heavy metadata dirty'ing operations.  Btrfs generates a lot
> more dirty metadata than most, partly why my attempt to deal with this was tied
> to using balance dirty pages since it already has all of the backoff logic.

That's an orthorgonal problem, I think. We still need the IO-less
reclaim in XFS regardless of how we throttle build up of dirty
metadata...

> Perhaps an explict balance_dirty_metadata() that we put after all
> metadata operations so we have a good way to throttle dirtiers
> when we aren't able to keep up?  Just a thought, based on my
> previous experiences trying to tackle this issue for btrfs, what
> you've done already may be enough to address these concerns.

The biggest issue is that different filesystems need different
mechanisms for throttling dirty metadata build-up. In ext4/XFS, the
amount of dirty metadata is bound by the log size, but that can
still be massively more metadata than the disk subsystem can handle
in a finite time.

IOWs, for XFS, the way to throttle dirty metadata buildup is to
limit the amount of log space we allow the filesystem to use when we
are able to throttle incoming transaction reservations. Nothing in
the VFS/mm subsystem can see any of this inside XFS, so I'm not
really sure how generic we could make a metadata dirtying throttle
implementation....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com


  reply index

Thread overview: 87+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-09  3:20 Dave Chinner
2019-10-09  3:20 ` [PATCH 01/26] xfs: Lower CIL flush limit for large logs Dave Chinner
2019-10-11 12:39   ` Brian Foster
2019-10-30 17:08   ` Darrick J. Wong
2019-10-09  3:21 ` [PATCH 02/26] xfs: Throttle commits on delayed background CIL push Dave Chinner
2019-10-11 12:38   ` Brian Foster
2019-10-09  3:21 ` [PATCH 03/26] xfs: don't allow log IO to be throttled Dave Chinner
2019-10-11  9:35   ` Christoph Hellwig
2019-10-11 12:39   ` Brian Foster
2019-10-30 17:14   ` Darrick J. Wong
2019-10-09  3:21 ` [PATCH 04/26] xfs: Improve metadata buffer reclaim accountability Dave Chinner
2019-10-11 12:39   ` Brian Foster
2019-10-11 12:57     ` Christoph Hellwig
2019-10-11 23:14       ` Dave Chinner
2019-10-11 23:13     ` Dave Chinner
2019-10-12 12:05       ` Brian Foster
2019-10-13  3:14         ` Dave Chinner
2019-10-14 13:05           ` Brian Foster
2019-10-30 17:25   ` Darrick J. Wong
2019-10-30 21:43     ` Dave Chinner
2019-10-31  3:06       ` Darrick J. Wong
2019-10-31 20:50         ` Dave Chinner
2019-10-31 21:05           ` Darrick J. Wong
2019-10-31 21:22             ` Christoph Hellwig
2019-11-03 21:26             ` Dave Chinner
2019-11-04 23:08               ` Darrick J. Wong
2019-10-09  3:21 ` [PATCH 05/26] xfs: correctly acount for reclaimable slabs Dave Chinner
2019-10-11 12:39   ` Brian Foster
2019-10-30 17:16   ` Darrick J. Wong
2019-10-09  3:21 ` [PATCH 06/26] xfs: synchronous AIL pushing Dave Chinner
2019-10-11  9:42   ` Christoph Hellwig
2019-10-11 12:40   ` Brian Foster
2019-10-11 23:15     ` Dave Chinner
2019-10-09  3:21 ` [PATCH 07/26] xfs: tail updates only need to occur when LSN changes Dave Chinner
2019-10-11  9:50   ` Christoph Hellwig
2019-10-11 12:40   ` Brian Foster
2019-10-09  3:21 ` [PATCH 08/26] mm: directed shrinker work deferral Dave Chinner
2019-10-14  8:46   ` Christoph Hellwig
2019-10-14 13:06     ` Brian Foster
2019-10-18  7:59     ` Dave Chinner
2019-10-09  3:21 ` [PATCH 09/26] shrinkers: use defer_work for GFP_NOFS sensitive shrinkers Dave Chinner
2019-10-09  3:21 ` [PATCH 10/26] mm: factor shrinker work calculations Dave Chinner
2019-10-09  3:21 ` [PATCH 11/26] shrinker: defer work only to kswapd Dave Chinner
2019-10-09  3:21 ` [PATCH 12/26] shrinker: clean up variable types and tracepoints Dave Chinner
2019-10-09  3:21 ` [PATCH 13/26] mm: reclaim_state records pages reclaimed, not slabs Dave Chinner
2019-10-09  3:21 ` [PATCH 14/26] mm: back off direct reclaim on excessive shrinker deferral Dave Chinner
2019-10-11 16:21   ` Matthew Wilcox
2019-10-11 23:20     ` Dave Chinner
2019-10-09  3:21 ` [PATCH 15/26] mm: kswapd backoff for shrinkers Dave Chinner
2019-10-09  3:21 ` [PATCH 16/26] xfs: synchronous AIL pushing Dave Chinner
2019-10-11 10:18   ` Christoph Hellwig
2019-10-11 15:29     ` Brian Foster
2019-10-11 23:27       ` Dave Chinner
2019-10-12 12:08         ` Brian Foster
2019-10-09  3:21 ` [PATCH 17/26] xfs: don't block kswapd in inode reclaim Dave Chinner
2019-10-11 15:29   ` Brian Foster
2019-10-09  3:21 ` [PATCH 18/26] xfs: reduce kswapd blocking on inode locking Dave Chinner
2019-10-11 10:29   ` Christoph Hellwig
2019-10-09  3:21 ` [PATCH 19/26] xfs: kill background reclaim work Dave Chinner
2019-10-11 10:31   ` Christoph Hellwig
2019-10-09  3:21 ` [PATCH 20/26] xfs: use AIL pushing for inode reclaim IO Dave Chinner
2019-10-11 17:38   ` Brian Foster
2019-10-09  3:21 ` [PATCH 21/26] xfs: remove mode from xfs_reclaim_inodes() Dave Chinner
2019-10-11 10:39   ` Christoph Hellwig
2019-10-14 13:07   ` Brian Foster
2019-10-09  3:21 ` [PATCH 22/26] xfs: track reclaimable inodes using a LRU list Dave Chinner
2019-10-11 10:42   ` Christoph Hellwig
2019-10-14 13:07   ` Brian Foster
2019-10-09  3:21 ` [PATCH 23/26] xfs: reclaim inodes from the LRU Dave Chinner
2019-10-11 10:56   ` Christoph Hellwig
2019-10-30 23:25     ` Dave Chinner
2019-10-09  3:21 ` [PATCH 24/26] xfs: remove unusued old inode reclaim code Dave Chinner
2019-10-09  3:21 ` [PATCH 25/26] xfs: rework unreferenced inode lookups Dave Chinner
2019-10-11 12:55   ` Christoph Hellwig
2019-10-11 13:39     ` Peter Zijlstra
2019-10-11 23:38     ` Dave Chinner
2019-10-14 13:07   ` Brian Foster
2019-10-17  1:24     ` Dave Chinner
2019-10-17  7:57       ` Brian Foster
2019-10-18 20:29         ` Dave Chinner
2019-10-09  3:21 ` [PATCH 26/26] xfs: use xfs_ail_push_all_sync in xfs_reclaim_inodes Dave Chinner
2019-10-11  9:55   ` Christoph Hellwig
2019-10-09  7:06 ` [PATCH V2 00/26] mm, xfs: non-blocking inode reclaim Christoph Hellwig
2019-10-11 19:03 ` Josef Bacik
2019-10-11 23:48   ` Dave Chinner [this message]
2019-10-12  0:19     ` Josef Bacik
2019-10-12  0:48       ` Dave Chinner

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