From: "Darrick J. Wong" <darrick.wong@oracle.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 01/26] xfs: Lower CIL flush limit for large logs Date: Wed, 30 Oct 2019 10:08:33 -0700 Message-ID: <20191030170833.GL15222@magnolia> (raw) In-Reply-To: <20191009032124.10541-2-david@fromorbit.com> On Wed, Oct 09, 2019 at 02:20:59PM +1100, Dave Chinner wrote: > From: Dave Chinner <dchinner@redhat.com> > > The current CIL size aggregation limit is 1/8th the log size. This > means for large logs we might be aggregating at least 250MB of dirty objects > in memory before the CIL is flushed to the journal. With CIL shadow > buffers sitting around, this means the CIL is often consuming >500MB > of temporary memory that is all allocated under GFP_NOFS conditions. > > Flushing the CIL can take some time to do if there is other IO > ongoing, and can introduce substantial log force latency by itself. > It also pins the memory until the objects are in the AIL and can be > written back and reclaimed by shrinkers. Hence this threshold also > tends to determine the minimum amount of memory XFS can operate in > under heavy modification without triggering the OOM killer. > > Modify the CIL space limit to prevent such huge amounts of pinned > metadata from aggregating. We can have 2MB of log IO in flight at > once, so limit aggregation to 16x this size. This threshold was > chosen as it little impact on performance (on 16-way fsmark) or log > traffic but pins a lot less memory on large logs especially under > heavy memory pressure. An aggregation limit of 8x had 5-10% > performance degradation and a 50% increase in log throughput for > the same workload, so clearly that was too small for highly > concurrent workloads on large logs. > > This was found via trace analysis of AIL behaviour. e.g. insertion > from a single CIL flush: > > xfs_ail_insert: old lsn 0/0 new lsn 1/3033090 type XFS_LI_INODE flags IN_AIL > > $ grep xfs_ail_insert /mnt/scratch/s.t |grep "new lsn 1/3033090" |wc -l > 1721823 > $ > > So there were 1.7 million objects inserted into the AIL from this > CIL checkpoint, the first at 2323.392108, the last at 2325.667566 which > was the end of the trace (i.e. it hadn't finished). Clearly a major > problem. > > Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> --D > --- > fs/xfs/xfs_log_priv.h | 29 +++++++++++++++++++++++------ > 1 file changed, 23 insertions(+), 6 deletions(-) > > diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h > index b880c23cb6e4..a3cc8a9a16d9 100644 > --- a/fs/xfs/xfs_log_priv.h > +++ b/fs/xfs/xfs_log_priv.h > @@ -323,13 +323,30 @@ struct xfs_cil { > * tries to keep 25% of the log free, so we need to keep below that limit or we > * risk running out of free log space to start any new transactions. > * > - * In order to keep background CIL push efficient, we will set a lower > - * threshold at which background pushing is attempted without blocking current > - * transaction commits. A separate, higher bound defines when CIL pushes are > - * enforced to ensure we stay within our maximum checkpoint size bounds. > - * threshold, yet give us plenty of space for aggregation on large logs. > + * In order to keep background CIL push efficient, we only need to ensure the > + * CIL is large enough to maintain sufficient in-memory relogging to avoid > + * repeated physical writes of frequently modified metadata. If we allow the CIL > + * to grow to a substantial fraction of the log, then we may be pinning hundreds > + * of megabytes of metadata in memory until the CIL flushes. This can cause > + * issues when we are running low on memory - pinned memory cannot be reclaimed, > + * and the CIL consumes a lot of memory. Hence we need to set an upper physical > + * size limit for the CIL that limits the maximum amount of memory pinned by the > + * CIL but does not limit performance by reducing relogging efficiency > + * significantly. > + * > + * As such, the CIL push threshold ends up being the smaller of two thresholds: > + * - a threshold large enough that it allows CIL to be pushed and progress to be > + * made without excessive blocking of incoming transaction commits. This is > + * defined to be 12.5% of the log space - half the 25% push threshold of the > + * AIL. > + * - small enough that it doesn't pin excessive amounts of memory but maintains > + * close to peak relogging efficiency. This is defined to be 16x the iclog > + * buffer window (32MB) as measurements have shown this to be roughly the > + * point of diminishing performance increases under highly concurrent > + * modification workloads. > */ > -#define XLOG_CIL_SPACE_LIMIT(log) (log->l_logsize >> 3) > +#define XLOG_CIL_SPACE_LIMIT(log) \ > + min_t(int, (log)->l_logsize >> 3, BBTOB(XLOG_TOTAL_REC_SHIFT(log)) << 4) > > /* > * ticket grant locks, queues and accounting have their own cachlines > -- > 2.23.0.rc1 >
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 [this message] 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 2019-10-12 0:19 ` Josef Bacik 2019-10-12 0:48 ` Dave Chinner
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