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From: Brian Foster <bfoster@redhat.com>
To: Dave Chinner <david@fromorbit.com>
Cc: linux-xfs@vger.kernel.org, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 17/24] xfs: don't block kswapd in inode reclaim
Date: Wed, 7 Aug 2019 07:14:10 -0400	[thread overview]
Message-ID: <20190807111410.GB19707@bfoster> (raw)
In-Reply-To: <20190806212704.GI7777@dread.disaster.area>

On Wed, Aug 07, 2019 at 07:27:04AM +1000, Dave Chinner wrote:
> On Tue, Aug 06, 2019 at 02:21:31PM -0400, Brian Foster wrote:
> > On Thu, Aug 01, 2019 at 12:17:45PM +1000, Dave Chinner wrote:
> > > From: Dave Chinner <dchinner@redhat.com>
> > > 
> > > We have a number of reasons for blocking kswapd in XFS inode
> > > reclaim, mainly all to do with the fact that memory reclaim has no
> > > feedback mechanisms to throttle on dirty slab objects that need IO
> > > to reclaim.
> > > 
> > > As a result, we currently throttle inode reclaim by issuing IO in
> > > the reclaim context. The unfortunate side effect of this is that it
> > > can cause long tail latencies in reclaim and for some workloads this
> > > can be a problem.
> > > 
> > > Now that the shrinkers finally have a method of telling kswapd to
> > > back off, we can start the process of making inode reclaim in XFS
> > > non-blocking. The first thing we need to do is not block kswapd, but
> > > so that doesn't cause immediate serious problems, make sure inode
> > > writeback is always underway when kswapd is running.
> > > 
> > > Signed-off-by: Dave Chinner <dchinner@redhat.com>
> > > ---
> > >  fs/xfs/xfs_icache.c | 17 ++++++++++++++---
> > >  1 file changed, 14 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
> > > index 0b0fd10a36d4..2fa2f8dcf86b 100644
> > > --- a/fs/xfs/xfs_icache.c
> > > +++ b/fs/xfs/xfs_icache.c
> > > @@ -1378,11 +1378,22 @@ xfs_reclaim_inodes_nr(
> > >  	struct xfs_mount	*mp,
> > >  	int			nr_to_scan)
> > >  {
> > > -	/* kick background reclaimer and push the AIL */
> > > +	int			sync_mode = SYNC_TRYLOCK;
> > > +
> > > +	/* kick background reclaimer */
> > >  	xfs_reclaim_work_queue(mp);
> > > -	xfs_ail_push_all(mp->m_ail);
> > >  
> > > -	return xfs_reclaim_inodes_ag(mp, SYNC_TRYLOCK | SYNC_WAIT, &nr_to_scan);
> > > +	/*
> > > +	 * For kswapd, we kick background inode writeback. For direct
> > > +	 * reclaim, we issue and wait on inode writeback to throttle
> > > +	 * reclaim rates and avoid shouty OOM-death.
> > > +	 */
> > > +	if (current_is_kswapd())
> > > +		xfs_ail_push_all(mp->m_ail);
> > 
> > So we're unblocking kswapd from dirty items, but we already kick the AIL
> > regardless of kswapd or not in inode reclaim. Why the change to no
> > longer kick the AIL in the !kswapd case? Whatever the reasoning, a
> > mention in the commit log would be helpful...
> 
> Because we used to block reclaim, we never knew how long it would be
> before it came back (say it had to write 1024 inode buffers), so
> every time we entered reclaim here we kicked the AIL in case we did
> get blocked for a long time.
> 
> Now kswapd doesn't block at all, we know it's going to enter this
> code repeatedly while direct reclaim is blocked, and so we only need
> it to kick background inode writeback via kswapd rather than all
> reclaim now.
> 

Got it. Can you include this reasoning in the commit log description
please?

Brian

> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@fromorbit.com

  reply	other threads:[~2019-08-07 11:14 UTC|newest]

Thread overview: 87+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-01  2:17 [RFC] [PATCH 00/24] mm, xfs: non-blocking inode reclaim Dave Chinner
2019-08-01  2:17 ` [PATCH 01/24] mm: directed shrinker work deferral Dave Chinner
2019-08-02 15:27   ` Brian Foster
2019-08-04  1:49     ` Dave Chinner
2019-08-05 17:42       ` Brian Foster
2019-08-05 23:43         ` Dave Chinner
2019-08-06 12:27           ` Brian Foster
2019-08-06 22:22             ` Dave Chinner
2019-08-07 11:13               ` Brian Foster
2019-08-01  2:17 ` [PATCH 02/24] shrinkers: use will_defer for GFP_NOFS sensitive shrinkers Dave Chinner
2019-08-02 15:27   ` Brian Foster
2019-08-04  1:50     ` Dave Chinner
2019-08-01  2:17 ` [PATCH 03/24] mm: factor shrinker work calculations Dave Chinner
2019-08-02 15:08   ` Nikolay Borisov
2019-08-04  2:05     ` Dave Chinner
2019-08-02 15:31   ` Brian Foster
2019-08-01  2:17 ` [PATCH 04/24] shrinker: defer work only to kswapd Dave Chinner
2019-08-02 15:34   ` Brian Foster
2019-08-04 16:48   ` Nikolay Borisov
2019-08-04 21:37     ` Dave Chinner
2019-08-07 16:12   ` kbuild test robot
2019-08-07 18:00   ` kbuild test robot
2019-08-01  2:17 ` [PATCH 05/24] shrinker: clean up variable types and tracepoints Dave Chinner
2019-08-01  2:17 ` [PATCH 06/24] mm: reclaim_state records pages reclaimed, not slabs Dave Chinner
2019-08-01  2:17 ` [PATCH 07/24] mm: back off direct reclaim on excessive shrinker deferral Dave Chinner
2019-08-01  2:17 ` [PATCH 08/24] mm: kswapd backoff for shrinkers Dave Chinner
2019-08-01  2:17 ` [PATCH 09/24] xfs: don't allow log IO to be throttled Dave Chinner
2019-08-01 13:39   ` Chris Mason
2019-08-01 23:58     ` Dave Chinner
2019-08-02  8:12       ` Christoph Hellwig
2019-08-02 14:11       ` Chris Mason
2019-08-02 18:34         ` Matthew Wilcox
2019-08-02 23:28         ` Dave Chinner
2019-08-05 18:32           ` Chris Mason
2019-08-05 23:09             ` Dave Chinner
2019-08-01  2:17 ` [PATCH 10/24] xfs: fix missed wakeup on l_flush_wait Dave Chinner
2019-08-01  2:17 ` [PATCH 11/24] xfs:: account for memory freed from metadata buffers Dave Chinner
2019-08-01  8:16   ` Christoph Hellwig
2019-08-01  9:21     ` Dave Chinner
2019-08-06  5:51       ` Christoph Hellwig
2019-08-01  2:17 ` [PATCH 12/24] xfs: correctly acount for reclaimable slabs Dave Chinner
2019-08-06  5:52   ` Christoph Hellwig
2019-08-06 21:05     ` Dave Chinner
2019-08-01  2:17 ` [PATCH 13/24] xfs: synchronous AIL pushing Dave Chinner
2019-08-05 17:51   ` Brian Foster
2019-08-05 23:21     ` Dave Chinner
2019-08-06 12:29       ` Brian Foster
2019-08-01  2:17 ` [PATCH 14/24] xfs: tail updates only need to occur when LSN changes Dave Chinner
2019-08-05 17:53   ` Brian Foster
2019-08-05 23:28     ` Dave Chinner
2019-08-06  5:33       ` Dave Chinner
2019-08-06 12:53         ` Brian Foster
2019-08-06 21:11           ` Dave Chinner
2019-08-01  2:17 ` [PATCH 15/24] xfs: eagerly free shadow buffers to reduce CIL footprint Dave Chinner
2019-08-05 18:03   ` Brian Foster
2019-08-05 23:33     ` Dave Chinner
2019-08-06 12:57       ` Brian Foster
2019-08-06 21:21         ` Dave Chinner
2019-08-01  2:17 ` [PATCH 16/24] xfs: Lower CIL flush limit for large logs Dave Chinner
2019-08-04 17:12   ` Nikolay Borisov
2019-08-01  2:17 ` [PATCH 17/24] xfs: don't block kswapd in inode reclaim Dave Chinner
2019-08-06 18:21   ` Brian Foster
2019-08-06 21:27     ` Dave Chinner
2019-08-07 11:14       ` Brian Foster [this message]
2019-08-01  2:17 ` [PATCH 18/24] xfs: reduce kswapd blocking on inode locking Dave Chinner
2019-08-06 18:22   ` Brian Foster
2019-08-06 21:33     ` Dave Chinner
2019-08-07 11:30       ` Brian Foster
2019-08-07 23:16         ` Dave Chinner
2019-08-01  2:17 ` [PATCH 19/24] xfs: kill background reclaim work Dave Chinner
2019-08-01  2:17 ` [PATCH 20/24] xfs: use AIL pushing for inode reclaim IO Dave Chinner
2019-08-07 18:09   ` Brian Foster
2019-08-07 23:10     ` Dave Chinner
2019-08-08 16:20       ` Brian Foster
2019-08-01  2:17 ` [PATCH 21/24] xfs: remove mode from xfs_reclaim_inodes() Dave Chinner
2019-08-01  2:17 ` [PATCH 22/24] xfs: track reclaimable inodes using a LRU list Dave Chinner
2019-08-08 16:36   ` Brian Foster
2019-08-09  0:10     ` Dave Chinner
2019-08-01  2:17 ` [PATCH 23/24] xfs: reclaim inodes from the LRU Dave Chinner
2019-08-08 16:39   ` Brian Foster
2019-08-09  1:20     ` Dave Chinner
2019-08-09 12:36       ` Brian Foster
2019-08-11  2:17         ` Dave Chinner
2019-08-11 12:46           ` Brian Foster
2019-08-01  2:17 ` [PATCH 24/24] xfs: remove unusued old inode reclaim code Dave Chinner
2019-08-06  5:57 ` [RFC] [PATCH 00/24] mm, xfs: non-blocking inode reclaim Christoph Hellwig
2019-08-06 21:37   ` Dave Chinner

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