From: Brian Foster <bfoster@redhat.com> To: Dave Chinner <david@fromorbit.com> Cc: Christoph Hellwig <hch@infradead.org>, linux-xfs@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 16/26] xfs: synchronous AIL pushing Date: Sat, 12 Oct 2019 08:08:36 -0400 Message-ID: <20191012120836.GB3307@bfoster> (raw) In-Reply-To: <20191011232716.GO16973@dread.disaster.area> On Sat, Oct 12, 2019 at 10:27:16AM +1100, Dave Chinner wrote: > On Fri, Oct 11, 2019 at 11:29:45AM -0400, Brian Foster wrote: > > 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. > > I probably forgot because this code gets removed at the end of the > series. Hence I haven't cared about exact correctness of neatness > as it's just temporary scaffolding to keep stuff from breaking > horribly as the changeover to non-blocking algorithms is done. > > It works well enough that I can't break it as it stands - I've > tested each patch individually with both load and fstests, and so > this code as it stands doesn't introduce any bisect landmines - it > prevents a bunch of problems in OOM conditions by retaining the > blocking behaviour of reclaim until we no longer need it... > Ok, I guess I forgot that this was temporary. FWIW, I think it's worth fixing the small things like this comparison and the couple things Christoph points out, if nothing else to facilitate review. Disregard the larger refactoring feedback.. Brian > > > > + 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). > > Oh, right. I'll fix that. > > > > 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(). > > The whole thing goes away, so there is zero point in trying to > optimise or perfect this code. It's temporary code, treat it as > such. > > Cheers, > > Dave. > -- > Dave Chinner > david@fromorbit.com
next prev parent 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 2019-10-11 23:27 ` Dave Chinner 2019-10-12 12:08 ` Brian Foster [this message] 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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