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Subject[PATCH] vfs: avoid call to inode_lru_list_del() if possible
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Le mercredi 27 juillet 2011 à 16:44 -0400, Christoph Hellwig a écrit :
> On Wed, Jul 27, 2011 at 05:21:05PM +0200, Eric Dumazet wrote:
> > If I am not mistaken, we can add unlocked checks on the three hot spots.
> >
> > After following patch, a close(socket(PF_INET, SOCK_DGRAM, 0)) pair on
> > my dev machine takes ~3us instead of ~9us.
> >
> > Maybe its better to split it in three patches, just let me know.
>
> I think three patches would be a lot cleaner.
>
> As for safety of the unlocked checks:
>
> - inode are either hashed when created or never, so that one looks
> fine.
> - same for the sb list.
> - the writeback list is a bit more dynamic as we move things around
> quite a bit. But in additon to the inode_wb_list_del call from
> evict() it only ever gets remove in writeback_single_inode, which
> for a freeing inode can only be called from the callers of evict().
>
> Btw, I wonder if you should micro-optimize things a bit further by
> moving the unhashed checks from the deletion functions into the callers
> and thus save a function call for each of them.
>

Here is the last patch, addressing inode_lru_list_del() call.

Only the call done from iput_final() can obviously benefit from checking
i_lru being empty or not, so it makes sense to perform the check at
caller site instead of doing it in inode_lru_list_del()

[PATCH] vfs: avoid call to inode_lru_list_del() if possible

inode_lru_list_del() is expensive because of per superblock lru locking,
while some inodes are not in lru list.

Adding a check in iput_final() can speedup pipe/sockets workloads on
SMP.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
---
fs/inode.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/inode.c b/fs/inode.c
index d0c72ff..b8b8939 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1328,7 +1328,8 @@ static void iput_final(struct inode *inode)
}

inode->i_state |= I_FREEING;
- inode_lru_list_del(inode);
+ if (!list_empty(&inode->i_lru))
+ inode_lru_list_del(inode);
spin_unlock(&inode->i_lock);

evict(inode);

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