[PATCH 5/5] fs: don't set *REFERENCED unless we are on the lru list

[Josef Bacik <jbacik@fb.com>]

With anything that populates the inode/dentry cache with a lot of one time use
inodes we can really put a lot of pressure on the system for things we don't
need to keep in cache.  It takes two runs through the LRU to evict these one use
entries, and if you have a lot of memory you can end up with 10's of millions of
entries in the dcache or icache that have never actually been touched since they
were first instantiated, and it will take a lot of CPU and a lot of pressure to
evict all of them.

So instead do what we do with pagecache, only set the *REFERENCED flags if we
are being used after we've been put onto the LRU.  This makes a significant
difference in the system's ability to evict these useless cache entries.  With a
fs_mark workload that creates 40 million files we get the following results (all
in files/sec)

Btrfs			Patched		Unpatched
Average Files/sec:	72209.3		63254.2
p50 Files/sec:		70850		57560
p90 Files/sec:		68757		53085
p99 Files/sec:		68757		53085

XFS			Patched		Unpatched
Average Files/sec:	61025.5		60719.5
p50 Files/sec:		60107		59465
p90 Files/sec: 		59300		57966
p99 Files/sec: 		59227		57528

Ext4			Patched		Unpatched
Average Files/sec:	121785.4	119248.0
p50 Files/sec:		120852		119274
p90 Files/sec:		116703		112783
p99 Files/sec:		114393		104934

The reason Btrfs has a much larger improvement is because it holds a lot more
things in memory so benefits more from faster slab reclaim, but across the board
is an improvement for each of the file systems.

Signed-off-by: Josef Bacik <jbacik@fb.com>
---
 fs/dcache.c | 15 ++++++++++-----
 fs/inode.c  |  5 ++++-
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 5c7cc95..a558075 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -779,8 +779,6 @@ repeat:
 			goto kill_it;
 	}
 
-	if (!(dentry->d_flags & DCACHE_REFERENCED))
-		dentry->d_flags |= DCACHE_REFERENCED;
 	dentry_lru_add(dentry);
 
 	dentry->d_lockref.count--;
@@ -803,6 +801,13 @@ static inline void __dget_dlock(struct dentry *dentry)
 	dentry->d_lockref.count++;
 }
 
+static inline void __dget_dlock_reference(struct dentry *dentry)
+{
+	if (dentry->d_flags & DCACHE_LRU_LIST)
+		dentry->d_flags |= DCACHE_REFERENCED;
+	dentry->d_lockref.count++;
+}
+
 static inline void __dget(struct dentry *dentry)
 {
 	lockref_get(&dentry->d_lockref);
@@ -875,7 +880,7 @@ again:
 			    (alias->d_flags & DCACHE_DISCONNECTED)) {
 				discon_alias = alias;
 			} else {
-				__dget_dlock(alias);
+				__dget_dlock_reference(alias);
 				spin_unlock(&alias->d_lock);
 				return alias;
 			}
@@ -886,7 +891,7 @@ again:
 		alias = discon_alias;
 		spin_lock(&alias->d_lock);
 		if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
-			__dget_dlock(alias);
+			__dget_dlock_reference(alias);
 			spin_unlock(&alias->d_lock);
 			return alias;
 		}
@@ -2250,7 +2255,7 @@ struct dentry *__d_lookup(const struct dentry *parent, const struct qstr *name)
 		if (!d_same_name(dentry, parent, name))
 			goto next;
 
-		dentry->d_lockref.count++;
+		__dget_dlock_reference(dentry);
 		found = dentry;
 		spin_unlock(&dentry->d_lock);
 		break;
diff --git a/fs/inode.c b/fs/inode.c
index 7e3ef3a..5937d3a 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -796,6 +796,8 @@ repeat:
 			__wait_on_freeing_inode(inode);
 			goto repeat;
 		}
+		if (!list_empty(&inode->i_lru))
+			inode->i_state |= I_REFERENCED;
 		__iget(inode);
 		spin_unlock(&inode->i_lock);
 		return inode;
@@ -823,6 +825,8 @@ repeat:
 			__wait_on_freeing_inode(inode);
 			goto repeat;
 		}
+		if (!list_empty(&inode->i_lru))
+			inode->i_state |= I_REFERENCED;
 		__iget(inode);
 		spin_unlock(&inode->i_lock);
 		return inode;
@@ -1463,7 +1467,6 @@ static void iput_final(struct inode *inode)
 		drop = generic_drop_inode(inode);
 
 	if (!drop && (sb->s_flags & MS_ACTIVE)) {
-		inode->i_state |= I_REFERENCED;
 		inode_add_lru(inode);
 		spin_unlock(&inode->i_lock);
 		return;
-- 
2.7.4