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From: Dave Chinner <david@fromorbit.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: linux-xfs@vger.kernel.org, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 23/26] xfs: reclaim inodes from the LRU
Date: Thu, 31 Oct 2019 10:25:38 +1100
Message-ID: <20191030232538.GR4614@dread.disaster.area> (raw)
In-Reply-To: <20191011105618.GE12811@infradead.org>

On Fri, Oct 11, 2019 at 03:56:18AM -0700, Christoph Hellwig wrote:
> > +++ b/fs/xfs/xfs_icache.c
> > @@ -1193,7 +1193,7 @@ xfs_reclaim_inode(
> >   *
> >   * Return the number of inodes freed.
> >   */
> > -STATIC int
> > +int
> >  xfs_reclaim_inodes_ag(
> >  	struct xfs_mount	*mp,
> >  	int			flags,
> 
> This looks odd.  This function actually is unused now.  I think you
> want to fold in the patch that removes it instead of this little hack
> to make the compiler happy.

I think it might have been a stray.

> 
> > -	xfs_reclaim_inodes_ag(mp, SYNC_WAIT, INT_MAX);
> > +        struct xfs_ireclaim_args *ra = arg;
> > +        struct inode		*inode = container_of(item, struct inode, i_lru);
> > +        struct xfs_inode	*ip = XFS_I(inode);
> 
> Whitespace damage, and a line > 80 chars.

Fixed.
> 
> > +out_ifunlock:
> > +	xfs_ifunlock(ip);
> 
> This error path will instantly deadlock, given that xfs_ifunlock takes
> i_flags_lock through xfs_iflags_clear, and we already hold it here.

Good catch. Clearly it's hard to hit a flush locked inode here...

> > +	/*
> > +	 * Remove the inode from the per-AG radix tree.
> > +	 *
> > +	 * Because radix_tree_delete won't complain even if the item was never
> > +	 * added to the tree assert that it's been there before to catch
> > +	 * problems with the inode life time early on.
> > +	 */
> > +	pag = xfs_perag_get(mp, XFS_INO_TO_AGNO(mp, ino));
> > +	spin_lock(&pag->pag_ici_lock);
> > +	if (!radix_tree_delete(&pag->pag_ici_root, XFS_INO_TO_AGINO(mp, ino)))
> > +		ASSERT(0);
> 
> Well, it "complains" by returning NULL instead of the entry.  So I think
> that comment could use some updates or simply be removed.

Removed.

> 
> > +void
> > +xfs_dispose_inodes(
> > +	struct list_head	*freeable)
> > +{
> > +	while (!list_empty(freeable)) {
> > +		struct inode *inode;
> > +
> > +		inode = list_first_entry(freeable, struct inode, i_lru);
> 
> This could use list_first_entry_or_null in the while loop, or not.
> Or list_pop_entry if we had it, but Linus hates that :)

Changed to use list_first_entry_or_null().

> 
> > +xfs_reclaim_inodes(
> > +	struct xfs_mount	*mp)
> > +{
> > +	while (list_lru_count(&mp->m_inode_lru)) {
> > +		struct xfs_ireclaim_args ra;
> > +		long freed, to_free;
> > +
> > +		INIT_LIST_HEAD(&ra.freeable);
> > +		ra.lowest_lsn = NULLCOMMITLSN;
> > +		to_free = list_lru_count(&mp->m_inode_lru);
> 
> Do we want a helper to initialize the xfs_ireclaim_args?  That would
> solve the "issue" of not initializing dirty_skipped in a few users
> and make it a little easier to use.

Done.

> > +
> > +		freed = list_lru_walk(&mp->m_inode_lru, xfs_inode_reclaim_isolate,
> 
> Line > 80 chars.

Fixed.

> > +static inline int __xfs_iflock_nowait(struct xfs_inode *ip)
> > +{
> > +	if (ip->i_flags & XFS_IFLOCK)
> > +		return false;
> > +	ip->i_flags |= XFS_IFLOCK;
> > +	return true;
> > +}
> 
> I wonder if simply open coding this would be simpler, given how magic
> xfs_inode_reclaim_isolate already is, and given that we really shouldn't
> use this helper anywhere else.

Well, I kind of just added an __xfs_ifunlock() wrapper to pair with
it because of the deadlock you caught above. I've added
lockdep_assert_held() to both of them to indicate the context in
which they should be used. While it's special case, I really would
like to keep the internals of flush locking code together as much as
possible.

Longer term (i.e. a future patchset), I really want to clean up how
we use the i_flags_lock and the i_flags bits. At the time the iflags
wrappers made sense, but now we have as many open coded flags as we
do wrapped. And in many of these cases I think we'd be better off
using bitops for them (e.g. bitops for the flush lock bit make these
new helpers go away), and the i_flags_lock can be removed and
replaced by the VFS inode i_lock for operations that require an
internal spinlock to serialise...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com


  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
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 [this message]
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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