From: Brian Foster <bfoster@redhat.com>
To: Dave Chinner <david@fromorbit.com>
Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 28/28] xfs: rework unreferenced inode lookups
Date: Tue, 19 Nov 2019 10:13:44 -0500 [thread overview]
Message-ID: <20191119151344.GD10763@bfoster> (raw)
In-Reply-To: <20191118010047.GS4614@dread.disaster.area>
On Mon, Nov 18, 2019 at 12:00:47PM +1100, Dave Chinner wrote:
> On Fri, Nov 15, 2019 at 12:26:00PM -0500, Brian Foster wrote:
> > On Fri, Nov 15, 2019 at 09:16:02AM +1100, Dave Chinner wrote:
> > > On Wed, Nov 06, 2019 at 05:18:46PM -0500, Brian Foster wrote:
> > > If so, most of this patch will go away....
> > >
> > > > > + * attached to the buffer so we don't need to do anything more here.
> > > > > */
> > > > > - if (ip != free_ip) {
> > > > > - if (!xfs_ilock_nowait(ip, XFS_ILOCK_EXCL)) {
> > > > > - rcu_read_unlock();
> > > > > - delay(1);
> > > > > - goto retry;
> > > > > - }
> > > > > -
> > > > > - /*
> > > > > - * Check the inode number again in case we're racing with
> > > > > - * freeing in xfs_reclaim_inode(). See the comments in that
> > > > > - * function for more information as to why the initial check is
> > > > > - * not sufficient.
> > > > > - */
> > > > > - if (ip->i_ino != inum) {
> > > > > + if (__xfs_iflags_test(ip, XFS_ISTALE)) {
> > > >
> > > > Is there a correctness reason for why we move the stale check to under
> > > > ilock (in both iflush/ifree)?
> > >
> > > It's under the i_flags_lock, and so I moved it up under the lookup
> > > hold of the i_flags_lock so we don't need to cycle it again.
> > >
> >
> > Yeah, but in both cases it looks like it moved to under the ilock as
> > well, which comes after i_flags_lock. IOW, why grab ilock for stale
> > inodes when we're just going to skip them?
>
> Because I was worrying about serialising against reclaim before
> changing the state of the inode. i.e. if the inode has already been
> isolated by not yet disposed of, we shouldn't touch the inode state
> at all. Serialisation against reclaim in this patch is via the
> ILOCK, hence we need to do that before setting ISTALE....
>
Yeah, I think my question still isn't clear... I'm not talking about
setting ISTALE. The code I referenced above is where we test for it and
skip the inode if it is already set. For example, the code referenced
above in xfs_ifree_get_one_inode() currently does the following with
respect to i_flags_lock, ILOCK and XFS_ISTALE:
...
spin_lock(i_flags_lock)
xfs_ilock_nowait(XFS_ILOCK_EXCL)
if !XFS_ISTALE
skip
set XFS_ISTALE
...
The reclaim isolate code does this, however:
spin_trylock(i_flags_lock)
if !XFS_ISTALE
skip
xfs_ilock(XFS_ILOCK_EXCL)
...
So my question is why not do something like the following in the
_get_one_inode() case?
...
spin_lock(i_flags_lock)
if !XFS_ISTALE
skip
xfs_ilock_nowait(XFS_ILOCK_EXCL)
set XFS_ISTALE
...
IOW, what is the need, if any, to acquire ilock in the iflush/ifree
paths before testing for XFS_ISTALE? Is there some specific intermediate
state I'm missing or is this just unintentional? The reason I ask is
ilock failure triggers that ugly delay(1) and retry thing, so it seems
slightly weird to allow that for a stale inode we're ultimately going to
skip (regardless of whether that would actually ever occur).
Brian
> IOWs, ISTALE is not protected by ILOCK, we just can't modify the
> inode state until after we've gained the ILOCK to protect against
> reclaim....
>
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@fromorbit.com
>
next prev parent reply other threads:[~2019-11-19 15:13 UTC|newest]
Thread overview: 72+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-31 23:45 [PATCH 00/28] mm, xfs: non-blocking inode reclaim Dave Chinner
2019-10-31 23:45 ` [PATCH 01/28] xfs: Lower CIL flush limit for large logs Dave Chinner
2019-10-31 23:45 ` [PATCH 02/28] xfs: Throttle commits on delayed background CIL push Dave Chinner
2019-11-01 12:04 ` Brian Foster
2019-11-01 21:40 ` Dave Chinner
2019-11-04 22:48 ` Darrick J. Wong
2019-10-31 23:45 ` [PATCH 03/28] xfs: don't allow log IO to be throttled Dave Chinner
2019-10-31 23:45 ` [PATCH 04/28] xfs: Improve metadata buffer reclaim accountability Dave Chinner
2019-11-01 12:05 ` Brian Foster
2019-11-04 23:21 ` Darrick J. Wong
2019-10-31 23:45 ` [PATCH 05/28] xfs: correctly acount for reclaimable slabs Dave Chinner
2019-10-31 23:45 ` [PATCH 06/28] xfs: factor common AIL item deletion code Dave Chinner
2019-11-04 23:16 ` Darrick J. Wong
2019-10-31 23:45 ` [PATCH 07/28] xfs: tail updates only need to occur when LSN changes Dave Chinner
2019-11-04 23:18 ` Darrick J. Wong
2019-10-31 23:45 ` [PATCH 08/28] xfs: factor inode lookup from xfs_ifree_cluster Dave Chinner
2019-11-01 12:05 ` Brian Foster
2019-11-04 23:20 ` Darrick J. Wong
2019-10-31 23:45 ` [PATCH 09/28] mm: directed shrinker work deferral Dave Chinner
2019-11-04 15:25 ` Brian Foster
2019-11-14 20:49 ` Dave Chinner
2019-11-15 17:21 ` Brian Foster
2019-11-18 0:49 ` Dave Chinner
2019-11-19 15:12 ` Brian Foster
2019-10-31 23:46 ` [PATCH 10/28] shrinkers: use defer_work for GFP_NOFS sensitive shrinkers Dave Chinner
2019-10-31 23:46 ` [PATCH 11/28] mm: factor shrinker work calculations Dave Chinner
2019-11-02 10:55 ` kbuild test robot
2019-11-04 15:29 ` Brian Foster
2019-11-14 20:59 ` Dave Chinner
2019-10-31 23:46 ` [PATCH 12/28] shrinker: defer work only to kswapd Dave Chinner
2019-11-04 15:29 ` Brian Foster
2019-11-14 21:11 ` Dave Chinner
2019-11-15 17:23 ` Brian Foster
2019-10-31 23:46 ` [PATCH 13/28] shrinker: clean up variable types and tracepoints Dave Chinner
2019-11-04 15:30 ` Brian Foster
2019-10-31 23:46 ` [PATCH 14/28] mm: reclaim_state records pages reclaimed, not slabs Dave Chinner
2019-11-04 19:58 ` Brian Foster
2019-10-31 23:46 ` [PATCH 15/28] mm: back off direct reclaim on excessive shrinker deferral Dave Chinner
2019-11-04 19:58 ` Brian Foster
2019-11-14 21:28 ` Dave Chinner
2019-10-31 23:46 ` [PATCH 16/28] mm: kswapd backoff for shrinkers Dave Chinner
2019-11-04 19:58 ` Brian Foster
2019-11-14 21:41 ` Dave Chinner
2019-10-31 23:46 ` [PATCH 17/28] xfs: synchronous AIL pushing Dave Chinner
2019-11-05 17:05 ` Brian Foster
2019-10-31 23:46 ` [PATCH 18/28] xfs: don't block kswapd in inode reclaim Dave Chinner
2019-10-31 23:46 ` [PATCH 19/28] xfs: reduce kswapd blocking on inode locking Dave Chinner
2019-11-05 17:05 ` Brian Foster
2019-10-31 23:46 ` [PATCH 20/28] xfs: kill background reclaim work Dave Chinner
2019-11-05 17:05 ` Brian Foster
2019-10-31 23:46 ` [PATCH 21/28] xfs: use AIL pushing for inode reclaim IO Dave Chinner
2019-11-05 17:06 ` Brian Foster
2019-10-31 23:46 ` [PATCH 22/28] xfs: remove mode from xfs_reclaim_inodes() Dave Chinner
2019-10-31 23:46 ` [PATCH 23/28] xfs: track reclaimable inodes using a LRU list Dave Chinner
2019-10-31 23:46 ` [PATCH 24/28] xfs: reclaim inodes from the LRU Dave Chinner
2019-11-06 17:21 ` Brian Foster
2019-11-14 21:51 ` Dave Chinner
2019-10-31 23:46 ` [PATCH 25/28] xfs: remove unusued old inode reclaim code Dave Chinner
2019-11-06 17:21 ` Brian Foster
2019-10-31 23:46 ` [PATCH 26/28] xfs: use xfs_ail_push_all in xfs_reclaim_inodes Dave Chinner
2019-11-06 17:22 ` Brian Foster
2019-11-14 21:53 ` Dave Chinner
2019-10-31 23:46 ` [PATCH 27/28] rwsem: introduce down/up_write_non_owner Dave Chinner
2019-10-31 23:46 ` [PATCH 28/28] xfs: rework unreferenced inode lookups Dave Chinner
2019-11-06 22:18 ` Brian Foster
2019-11-14 22:16 ` Dave Chinner
2019-11-15 13:13 ` Christoph Hellwig
2019-11-15 17:26 ` Brian Foster
2019-11-18 1:00 ` Dave Chinner
2019-11-19 15:13 ` Brian Foster [this message]
2019-11-19 21:18 ` Dave Chinner
2019-11-20 12:42 ` Brian Foster
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