1. 30 5月, 2011 5 次提交
  2. 29 5月, 2011 1 次提交
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      Cache xattr security drop check for write v2 · 69b45732
      Andi Kleen 提交于
      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: chris.mason@oracle.com
      Cc: josef@redhat.com
      Cc: viro@zeniv.linux.org.uk
      Cc: agruen@linbit.com
      Cc: Serge E. Hallyn <serue@us.ibm.com>
      Signed-off-by: NAndi Kleen <ak@linux.intel.com>
      Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      69b45732
  3. 28 5月, 2011 30 次提交
  4. 27 5月, 2011 4 次提交