On Tue, Oct 25, 2016 at 02:41:44PM -0400, Josef Bacik wrote:
> 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 <jba...@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);
This misses dentries that we get through __d_lookup_rcu(), so I think
your change made it so most things aren't getting DCACHE_REFERENCED set
at all. Maybe something like this instead?
diff --git a/fs/dcache.c b/fs/dcache.c
index 5c7cc95..d7a56a8 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -412,15 +412,6 @@ static void d_lru_shrink_move(struct list_lru_one *lru,
struct dentry *dentry,
list_lru_isolate_move(lru, &dentry->d_lru, list);
}
-/*
- * dentry_lru_(add|del)_list) must be called with d_lock held.
- */
-static void dentry_lru_add(struct dentry *dentry)
-{
- if (unlikely(!(dentry->d_flags & DCACHE_LRU_LIST)))
- d_lru_add(dentry);
-}
-
/**
* d_drop - drop a dentry
* @dentry: dentry to drop
@@ -779,9 +770,12 @@ void dput(struct dentry *dentry)
goto kill_it;
}
- if (!(dentry->d_flags & DCACHE_REFERENCED))
- dentry->d_flags |= DCACHE_REFERENCED;
- dentry_lru_add(dentry);
+ if (likely(dentry->d_flags & DCACHE_LRU_LIST)) {
+ if (!(dentry->d_flags & DCACHE_REFERENCED))
+ dentry->d_flags |= DCACHE_REFERENCED;
+ } else {
+ d_lru_add(dentry);
+ }
dentry->d_lockref.count--;
spin_unlock(&dentry->d_lock);
diff --git a/fs/inode.c b/fs/inode.c
index 88110fd..16faca3 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -798,6 +798,8 @@ static struct inode *find_inode(struct super_block *sb,
__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;
@@ -825,6 +827,8 @@ static struct inode *find_inode_fast(struct super_block *sb,
__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;
@@ -1492,7 +1496,6 @@ 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;
--
Omar
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