1. 13 7月, 2011 8 次提交
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    • D
      xfs: unpin stale inodes directly in IOP_COMMITTED · 1316d4da
      Dave Chinner 提交于
      When inodes are marked stale in a transaction, they are treated
      specially when the inode log item is being inserted into the AIL.
      It tries to avoid moving the log item forward in the AIL due to a
      race condition with the writing the underlying buffer back to disk.
      The was "fixed" in commit de25c181 ("xfs: avoid moving stale inodes
      in the AIL").
      
      To avoid moving the item forward, we return a LSN smaller than the
      commit_lsn of the completing transaction, thereby trying to trick
      the commit code into not moving the inode forward at all. I'm not
      sure this ever worked as intended - it assumes the inode is already
      in the AIL, but I don't think the returned LSN would have been small
      enough to prevent moving the inode. It appears that the reason it
      worked is that the lower LSN of the inodes meant they were inserted
      into the AIL and flushed before the inode buffer (which was moved to
      the commit_lsn of the transaction).
      
      The big problem is that with delayed logging, the returning of the
      different LSN means insertion takes the slow, non-bulk path.  Worse
      yet is that insertion is to a position -before- the commit_lsn so it
      is doing a AIL traversal on every insertion, and has to walk over
      all the items that have already been inserted into the AIL. It's
      expensive.
      
      To compound the matter further, with delayed logging inodes are
      likely to go from clean to stale in a single checkpoint, which means
      they aren't even in the AIL at all when we come across them at AIL
      insertion time. Hence these were all getting inserted into the AIL
      when they simply do not need to be as inodes marked XFS_ISTALE are
      never written back.
      
      Transactional/recovery integrity is maintained in this case by the
      other items in the unlink transaction that were modified (e.g. the
      AGI btree blocks) and committed in the same checkpoint.
      
      So to fix this, simply unpin the stale inodes directly in
      xfs_inode_item_committed() and return -1 to indicate that the AIL
      insertion code does not need to do any further processing of these
      inodes.
      Signed-off-by: NDave Chinner <dchinner@redhat.com>
      Reviewed-by: NChristoph Hellwig <hch@lst.de>
      Signed-off-by: NAlex Elder <aelder@sgi.com>
      1316d4da