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authorDave Chinner <dchinner@redhat.com>2010-12-20 12:02:19 +1100
committerDave Chinner <david@fromorbit.com>2010-12-20 12:02:19 +1100
commit0e57f6a36f9be03e5abb755f524ee91c4aebe854 (patch)
tree4de7d393444171525ca8c6b73026493ffa8e1b12 /Documentation/logo.gif
parenteb3efa1249b6413be930bdf13d10b6238028a440 (diff)
downloadlinux-0e57f6a36f9be03e5abb755f524ee91c4aebe854.tar.bz2
xfs: bulk AIL insertion during transaction commit
When inserting items into the AIL from the transaction committed callbacks, we take the AIL lock for every single item that is to be inserted. For a CIL checkpoint commit, this can be tens of thousands of individual inserts, yet almost all of the items will be inserted at the same point in the AIL because they have the same index. To reduce the overhead and contention on the AIL lock for such operations, introduce a "bulk insert" operation which allows a list of log items with the same LSN to be inserted in a single operation via a list splice. To do this, we need to pre-sort the log items being committed into a temporary list for insertion. The complexity is that not every log item will end up with the same LSN, and not every item is actually inserted into the AIL. Items that don't match the commit LSN will be inserted and unpinned as per the current one-at-a-time method (relatively rare), while items that are not to be inserted will be unpinned and freed immediately. Items that are to be inserted at the given commit lsn are placed in a temporary array and inserted into the AIL in bulk each time the array fills up. As a result of this, we trade off AIL hold time for a significant reduction in traffic. lock_stat output shows that the worst case hold time is unchanged, but contention from AIL inserts drops by an order of magnitude and the number of lock traversal decreases significantly. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de>
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