path: root/mm/filemap.c
diff options
authorAndi Kleen <>2011-05-28 08:25:51 -0700
committerAl Viro <>2011-05-28 12:02:09 -0400
commit69b4573296469fd3f70cf7044693074980517067 (patch)
treeaea41eacb2a0f32748145a59bb8dc300b4485f36 /mm/filemap.c
parentd76ee18a8551e33ad7dbd55cac38bc7b094f3abb (diff)
Cache xattr security drop check for write v2
Some recent benchmarking on btrfs showed that a major scaling bottleneck on large systems on btrfs is currently the xattr lookup on every write. Why xattr lookup on every write I hear you ask? write wants to drop suid and security related xattrs that could set o capabilities for executables. To do that it currently looks up security.capability on EVERY write (even for non executables) to decide whether to drop it or not. In btrfs this causes an additional tree walk, hitting some per file system locks and quite bad scalability. In a simple read workload on a 8S system I saw over 90% CPU time in spinlocks related to that. Chris Mason tells me this is also a problem in ext4, where it hits the global mbcache lock. This patch adds a simple per inode to avoid this problem. We only do the lookup once per file and then if there is no xattr cache the decision. All xattr changes clear the flag. I also used the same flag to avoid the suid check, although that one is pretty cheap. A file system can also set this flag when it creates the inode, if it has a cheap way to do so. This is done for some common file systems in followon patches. With this patch a major part of the lock contention disappears for btrfs. Some testing on smaller systems didn't show significant performance changes, but at least it helps the larger systems and is generally more efficient. v2: Rename is_sgid. add file system helper. Cc: Cc: Cc: Cc: Cc: Serge E. Hallyn <> Signed-off-by: Andi Kleen <> Signed-off-by: Al Viro <>
Diffstat (limited to 'mm/filemap.c')
1 files changed, 12 insertions, 2 deletions
diff --git a/mm/filemap.c b/mm/filemap.c
index dac95a24deac..d7b10578a64b 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1982,16 +1982,26 @@ static int __remove_suid(struct dentry *dentry, int kill)
int file_remove_suid(struct file *file)
struct dentry *dentry = file->f_path.dentry;
- int killsuid = should_remove_suid(dentry);
- int killpriv = security_inode_need_killpriv(dentry);
+ struct inode *inode = dentry->d_inode;
+ int killsuid;
+ int killpriv;
int error = 0;
+ /* Fast path for nothing security related */
+ if (IS_NOSEC(inode))
+ return 0;
+ killsuid = should_remove_suid(dentry);
+ killpriv = security_inode_need_killpriv(dentry);
if (killpriv < 0)
return killpriv;
if (killpriv)
error = security_inode_killpriv(dentry);
if (!error && killsuid)
error = __remove_suid(dentry, killsuid);
+ if (!error)
+ inode->i_flags |= S_NOSEC;
return error;