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From: Brian Foster <bfoster@redhat.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>,
	linux-xfs@vger.kernel.org, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 16/26] xfs: synchronous AIL pushing
Date: Fri, 11 Oct 2019 11:29:45 -0400
Message-ID: <20191011152945.GH61257@bfoster> (raw)
In-Reply-To: <20191011101825.GA29171@infradead.org>

On Fri, Oct 11, 2019 at 03:18:25AM -0700, Christoph Hellwig wrote:
> On Wed, Oct 09, 2019 at 02:21:14PM +1100, Dave Chinner wrote:
> > Factor the common AIL deletion code that does all the wakeups into a
> > helper so we only have one copy of this somewhat tricky code to
> > interface with all the wakeups necessary when the LSN of the log
> > tail changes.
> > 
> > xfs_ail_push_sync() is temporary infrastructure to facilitate
> > non-blocking, IO-less inode reclaim throttling that allows further
> > structural changes to be made. Once those structural changes are
> > made, the need for this function goes away and it is removed,
> > leaving us with only the xfs_ail_update_finish() factoring when this
> > is all done.
> 
> The xfs_ail_update_finish work here is in an earlier patch, so the
> changelog will need some updates.
> 
> > +	spin_lock(&ailp->ail_lock);
> > +	while ((lip = xfs_ail_min(ailp)) != NULL) {
> > +		prepare_to_wait(&ailp->ail_push, &wait, TASK_UNINTERRUPTIBLE);
> > +		if (XFS_FORCED_SHUTDOWN(ailp->ail_mount) ||
> > +		    XFS_LSN_CMP(threshold_lsn, lip->li_lsn) <= 0)

Wasn't this supposed to change to < 0? The rfc series had that logic,
but it changed from <= to < later in the wrong patch.

> > +			break;
> > +		/* XXX: cmpxchg? */
> > +		while (XFS_LSN_CMP(threshold_lsn, ailp->ail_target) > 0)
> > +			xfs_trans_ail_copy_lsn(ailp, &ailp->ail_target, &threshold_lsn);
> 
> This code looks broken on 32-bit given that xfs_trans_ail_copy_lsn takes
> the ail_lock there.  Just replacing the xfs_trans_ail_copy_lsn call with
> a direct assignment would fix that, no need for cmpxchg either as far
> as I can tell (and it would fix that too long line as well).
> 
> But a:
> 
> 		while (XFS_LSN_CMP(threshold_lsn, ailp->ail_target) > 0)
> 			ailp->ail_target = threshold_lsn;
> 
> still looks odd, I think this should simply be an if. 
> 
> > +		wake_up_process(ailp->ail_task);
> > +		spin_unlock(&ailp->ail_lock);
> 
> xfsaild will take ail_lock pretty quickly.  I think we should drop
> the lock before waking it.

Can't we replace this whole thing with something that repurposes
xfs_ail_push_all_sync()? That only requires some tweaks to the existing
function and the new _push_all_sync() wrapper ends up looking something
like:

	while ((threshold_lsn = xfs_ail_max_lsn(ailp)) != 0)
		xfs_ail_push_sync(ailp, threshold_lsn);

There's an extra lock cycle, but that's still only on tail updates. That
doesn't seem unreasonable to me for the usage of _push_all_sync().

Brian


  reply index

Thread overview: 87+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-09  3:20 [PATCH V2 00/26] mm, xfs: non-blocking inode reclaim 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 [this message]
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
2019-10-12  0:19     ` Josef Bacik
2019-10-12  0:48       ` Dave Chinner

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