[22/24] xfs: track reclaimable inodes using a LRU list
diff mbox series

Message ID 20190801021752.4986-23-david@fromorbit.com
State New
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Series
  • mm, xfs: non-blocking inode reclaim
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Commit Message

Dave Chinner Aug. 1, 2019, 2:17 a.m. UTC
From: Dave Chinner <dchinner@redhat.com>

Now that we don't do IO from the inode reclaim code, there is no
need to optimise inode scanning order for optimal IO
characteristics. The AIL takes care of that for us, so now reclaim
can focus on selecting the best inodes to reclaim.

Hence we can change the inode reclaim algorithm to a real LRU and
remove the need to use the radix tree to track and walk inodes under
reclaim. This frees up a radix tree bit and simplifies the code that
marks inodes are reclaim candidates. It also simplifies the reclaim
code - we don't need batching anymore and all the reclaim logic
can be added to the LRU isolation callback.

Further, we get node aware reclaim at the xfs_inode level, which
should help the per-node reclaim code free relevant inodes faster.

We can re-use the VFS inode lru pointers - once the inode has been
reclaimed from the VFS, we can use these pointers ourselves. Hence
we don't need to grow the inode to change the way we index
reclaimable inodes.

Start by adding the list_lru tracking in parallel with the existing
reclaim code. This makes it easier to see the LRU infrastructure
separate to the reclaim algorithm changes. Especially the locking
order, which is ip->i_flags_lock -> list_lru lock.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
 fs/xfs/xfs_icache.c | 31 +++++++------------------------
 fs/xfs/xfs_icache.h |  1 -
 fs/xfs/xfs_mount.h  |  1 +
 fs/xfs/xfs_super.c  | 31 ++++++++++++++++++++++++-------
 4 files changed, 32 insertions(+), 32 deletions(-)

Comments

Brian Foster Aug. 8, 2019, 4:36 p.m. UTC | #1
On Thu, Aug 01, 2019 at 12:17:50PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> Now that we don't do IO from the inode reclaim code, there is no
> need to optimise inode scanning order for optimal IO
> characteristics. The AIL takes care of that for us, so now reclaim
> can focus on selecting the best inodes to reclaim.
> 
> Hence we can change the inode reclaim algorithm to a real LRU and
> remove the need to use the radix tree to track and walk inodes under
> reclaim. This frees up a radix tree bit and simplifies the code that
> marks inodes are reclaim candidates. It also simplifies the reclaim
> code - we don't need batching anymore and all the reclaim logic
> can be added to the LRU isolation callback.
> 
> Further, we get node aware reclaim at the xfs_inode level, which
> should help the per-node reclaim code free relevant inodes faster.
> 
> We can re-use the VFS inode lru pointers - once the inode has been
> reclaimed from the VFS, we can use these pointers ourselves. Hence
> we don't need to grow the inode to change the way we index
> reclaimable inodes.
> 
> Start by adding the list_lru tracking in parallel with the existing
> reclaim code. This makes it easier to see the LRU infrastructure
> separate to the reclaim algorithm changes. Especially the locking
> order, which is ip->i_flags_lock -> list_lru lock.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
>  fs/xfs/xfs_icache.c | 31 +++++++------------------------
>  fs/xfs/xfs_icache.h |  1 -
>  fs/xfs/xfs_mount.h  |  1 +
>  fs/xfs/xfs_super.c  | 31 ++++++++++++++++++++++++-------
>  4 files changed, 32 insertions(+), 32 deletions(-)
> 
...
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index a59d3a21be5c..b5c4c1b6fd19 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
...
> @@ -1801,7 +1817,8 @@ xfs_fs_nr_cached_objects(
>  	/* Paranoia: catch incorrect calls during mount setup or teardown */
>  	if (WARN_ON_ONCE(!sb->s_fs_info))
>  		return 0;
> -	return xfs_reclaim_inodes_count(XFS_M(sb));
> +
> +	return list_lru_shrink_count(&XFS_M(sb)->m_inode_lru, sc);

Do we not need locking here, or are we just skipping it because this
apparently maintains a count field and accuracy isn't critical? If the
latter, a one liner comment would be useful.

Brian

>  }
>  
>  static long
> -- 
> 2.22.0
>
Dave Chinner Aug. 9, 2019, 12:10 a.m. UTC | #2
On Thu, Aug 08, 2019 at 12:36:53PM -0400, Brian Foster wrote:
> On Thu, Aug 01, 2019 at 12:17:50PM +1000, Dave Chinner wrote:
> > From: Dave Chinner <dchinner@redhat.com>
> > 
> > Now that we don't do IO from the inode reclaim code, there is no
> > need to optimise inode scanning order for optimal IO
> > characteristics. The AIL takes care of that for us, so now reclaim
> > can focus on selecting the best inodes to reclaim.
> > 
> > Hence we can change the inode reclaim algorithm to a real LRU and
> > remove the need to use the radix tree to track and walk inodes under
> > reclaim. This frees up a radix tree bit and simplifies the code that
> > marks inodes are reclaim candidates. It also simplifies the reclaim
> > code - we don't need batching anymore and all the reclaim logic
> > can be added to the LRU isolation callback.
> > 
> > Further, we get node aware reclaim at the xfs_inode level, which
> > should help the per-node reclaim code free relevant inodes faster.
> > 
> > We can re-use the VFS inode lru pointers - once the inode has been
> > reclaimed from the VFS, we can use these pointers ourselves. Hence
> > we don't need to grow the inode to change the way we index
> > reclaimable inodes.
> > 
> > Start by adding the list_lru tracking in parallel with the existing
> > reclaim code. This makes it easier to see the LRU infrastructure
> > separate to the reclaim algorithm changes. Especially the locking
> > order, which is ip->i_flags_lock -> list_lru lock.
> > 
> > Signed-off-by: Dave Chinner <dchinner@redhat.com>
> > ---
> >  fs/xfs/xfs_icache.c | 31 +++++++------------------------
> >  fs/xfs/xfs_icache.h |  1 -
> >  fs/xfs/xfs_mount.h  |  1 +
> >  fs/xfs/xfs_super.c  | 31 ++++++++++++++++++++++++-------
> >  4 files changed, 32 insertions(+), 32 deletions(-)
> > 
> ...
> > diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> > index a59d3a21be5c..b5c4c1b6fd19 100644
> > --- a/fs/xfs/xfs_super.c
> > +++ b/fs/xfs/xfs_super.c
> ...
> > @@ -1801,7 +1817,8 @@ xfs_fs_nr_cached_objects(
> >  	/* Paranoia: catch incorrect calls during mount setup or teardown */
> >  	if (WARN_ON_ONCE(!sb->s_fs_info))
> >  		return 0;
> > -	return xfs_reclaim_inodes_count(XFS_M(sb));
> > +
> > +	return list_lru_shrink_count(&XFS_M(sb)->m_inode_lru, sc);
> 
> Do we not need locking here,

No locking is needed - we have no global lock that protects the
list_lru that we could use to serialise the count - that would
completely destroy the scalability advantages the list_lru provide.
As it is, shrinker counts have always been inherently racy and so we
don't really care for accuracy anywhere in the shrinker code. Hence
there is no need to attempt to be accurate here, just like didn't
attempt to be accurate for the per AG reclaimable inode count
aggregation that this replaces.

> or are we just skipping it because this
> apparently maintains a count field and accuracy isn't critical? If the
> latter, a one liner comment would be useful.

I don't think it needs comments as they would be stating the
obvious.  We don't have comments explaining this in any other
shrinker - it's jsut assumed that anyone working with shrinkers
already knows that the counts are not required to be exactly
accurate...

Cheers,

Dave.

Patch
diff mbox series

diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
index aaa1f840a86c..610f643df9f6 100644
--- a/fs/xfs/xfs_icache.c
+++ b/fs/xfs/xfs_icache.c
@@ -370,12 +370,11 @@  xfs_iget_cache_hit(
 
 		/*
 		 * We need to set XFS_IRECLAIM to prevent xfs_reclaim_inode
-		 * from stomping over us while we recycle the inode.  We can't
-		 * clear the radix tree reclaimable tag yet as it requires
-		 * pag_ici_lock to be held exclusive.
+		 * from stomping over us while we recycle the inode. Remove it
+		 * from the LRU straight away so we can re-init the VFS inode.
 		 */
 		ip->i_flags |= XFS_IRECLAIM;
-
+		list_lru_del(&mp->m_inode_lru, &inode->i_lru);
 		spin_unlock(&ip->i_flags_lock);
 		rcu_read_unlock();
 
@@ -390,6 +389,7 @@  xfs_iget_cache_hit(
 			spin_lock(&ip->i_flags_lock);
 			wake = !!__xfs_iflags_test(ip, XFS_INEW);
 			ip->i_flags &= ~(XFS_INEW | XFS_IRECLAIM);
+			list_lru_add(&mp->m_inode_lru, &inode->i_lru);
 			if (wake)
 				wake_up_bit(&ip->i_flags, __XFS_INEW_BIT);
 			ASSERT(ip->i_flags & XFS_IRECLAIMABLE);
@@ -1141,6 +1141,9 @@  xfs_reclaim_inode(
 	ino = ip->i_ino; /* for radix_tree_delete */
 	ip->i_flags = XFS_IRECLAIM;
 	ip->i_ino = 0;
+
+	/* XXX: temporary until lru based reclaim */
+	list_lru_del(&pag->pag_mount->m_inode_lru, &VFS_I(ip)->i_lru);
 	spin_unlock(&ip->i_flags_lock);
 
 	xfs_iunlock(ip, XFS_ILOCK_EXCL);
@@ -1330,26 +1333,6 @@  xfs_reclaim_inodes_nr(
 	return xfs_reclaim_inodes_ag(mp, sync_mode, nr_to_scan);
 }
 
-/*
- * Return the number of reclaimable inodes in the filesystem for
- * the shrinker to determine how much to reclaim.
- */
-int
-xfs_reclaim_inodes_count(
-	struct xfs_mount	*mp)
-{
-	struct xfs_perag	*pag;
-	xfs_agnumber_t		ag = 0;
-	int			reclaimable = 0;
-
-	while ((pag = xfs_perag_get_tag(mp, ag, XFS_ICI_RECLAIM_TAG))) {
-		ag = pag->pag_agno + 1;
-		reclaimable += pag->pag_ici_reclaimable;
-		xfs_perag_put(pag);
-	}
-	return reclaimable;
-}
-
 STATIC int
 xfs_inode_match_id(
 	struct xfs_inode	*ip,
diff --git a/fs/xfs/xfs_icache.h b/fs/xfs/xfs_icache.h
index 1c9b9edb2986..0ab08b58cd45 100644
--- a/fs/xfs/xfs_icache.h
+++ b/fs/xfs/xfs_icache.h
@@ -50,7 +50,6 @@  struct xfs_inode * xfs_inode_alloc(struct xfs_mount *mp, xfs_ino_t ino);
 void xfs_inode_free(struct xfs_inode *ip);
 
 void xfs_reclaim_inodes(struct xfs_mount *mp);
-int xfs_reclaim_inodes_count(struct xfs_mount *mp);
 long xfs_reclaim_inodes_nr(struct xfs_mount *mp, int nr_to_scan);
 
 void xfs_inode_set_reclaim_tag(struct xfs_inode *ip);
diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index 2049e764faed..4a4ecbc22246 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -75,6 +75,7 @@  typedef struct xfs_mount {
 	uint8_t			m_rt_sick;
 
 	struct xfs_ail		*m_ail;		/* fs active log item list */
+	struct list_lru		m_inode_lru;
 
 	struct xfs_sb		m_sb;		/* copy of fs superblock */
 	spinlock_t		m_sb_lock;	/* sb counter lock */
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index a59d3a21be5c..b5c4c1b6fd19 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -919,28 +919,30 @@  xfs_fs_destroy_inode(
 	struct inode		*inode)
 {
 	struct xfs_inode	*ip = XFS_I(inode);
+	struct xfs_mount	*mp = ip->i_mount;
 
 	trace_xfs_destroy_inode(ip);
 
 	ASSERT(!rwsem_is_locked(&inode->i_rwsem));
-	XFS_STATS_INC(ip->i_mount, vn_rele);
-	XFS_STATS_INC(ip->i_mount, vn_remove);
+	XFS_STATS_INC(mp, vn_rele);
+	XFS_STATS_INC(mp, vn_remove);
 
 	xfs_inactive(ip);
 
-	if (!XFS_FORCED_SHUTDOWN(ip->i_mount) && ip->i_delayed_blks) {
+	if (!XFS_FORCED_SHUTDOWN(mp) && ip->i_delayed_blks) {
 		xfs_check_delalloc(ip, XFS_DATA_FORK);
 		xfs_check_delalloc(ip, XFS_COW_FORK);
 		ASSERT(0);
 	}
 
-	XFS_STATS_INC(ip->i_mount, vn_reclaim);
+	XFS_STATS_INC(mp, vn_reclaim);
 
 	/*
 	 * We should never get here with one of the reclaim flags already set.
 	 */
-	ASSERT_ALWAYS(!xfs_iflags_test(ip, XFS_IRECLAIMABLE));
-	ASSERT_ALWAYS(!xfs_iflags_test(ip, XFS_IRECLAIM));
+	spin_lock(&ip->i_flags_lock);
+	ASSERT_ALWAYS(!__xfs_iflags_test(ip, XFS_IRECLAIMABLE));
+	ASSERT_ALWAYS(!__xfs_iflags_test(ip, XFS_IRECLAIM));
 
 	/*
 	 * We always use background reclaim here because even if the
@@ -949,6 +951,9 @@  xfs_fs_destroy_inode(
 	 * this more efficiently than we can here, so simply let background
 	 * reclaim tear down all inodes.
 	 */
+	__xfs_iflags_set(ip, XFS_IRECLAIMABLE);
+	list_lru_add(&mp->m_inode_lru, &VFS_I(ip)->i_lru);
+	spin_unlock(&ip->i_flags_lock);
 	xfs_inode_set_reclaim_tag(ip);
 }
 
@@ -1541,6 +1546,15 @@  xfs_mount_alloc(
 	if (!mp)
 		return NULL;
 
+	/*
+	 * The inode lru needs to be associated with the superblock shrinker,
+	 * and like the rest of the superblock shrinker, it's memcg aware.
+	 */
+	if (list_lru_init_memcg(&mp->m_inode_lru, &sb->s_shrink)) {
+		kfree(mp);
+		return NULL;
+	}
+
 	mp->m_super = sb;
 	spin_lock_init(&mp->m_sb_lock);
 	spin_lock_init(&mp->m_agirotor_lock);
@@ -1748,6 +1762,7 @@  xfs_fs_fill_super(
  out_free_fsname:
 	sb->s_fs_info = NULL;
 	xfs_free_fsname(mp);
+	list_lru_destroy(&mp->m_inode_lru);
 	kfree(mp);
  out:
 	return error;
@@ -1780,6 +1795,7 @@  xfs_fs_put_super(
 
 	sb->s_fs_info = NULL;
 	xfs_free_fsname(mp);
+	list_lru_destroy(&mp->m_inode_lru);
 	kfree(mp);
 }
 
@@ -1801,7 +1817,8 @@  xfs_fs_nr_cached_objects(
 	/* Paranoia: catch incorrect calls during mount setup or teardown */
 	if (WARN_ON_ONCE(!sb->s_fs_info))
 		return 0;
-	return xfs_reclaim_inodes_count(XFS_M(sb));
+
+	return list_lru_shrink_count(&XFS_M(sb)->m_inode_lru, sc);
 }
 
 static long