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ocfs2: Add a mount option "coherency=*" to handle cluster coherency for O_DIRECT writes.

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Currently, the default behavior of O_DIRECT writes was allowing
concurrent writing among nodes to the same file, with no cluster
coherency guaranteed (no EX lock held).  This can leave stale data in
the cache for buffered reads on other nodes.

The new mount option introduce a chance to choose two different
behaviors for O_DIRECT writes:

    * coherency=full, as the default value, will disallow
                      concurrent O_DIRECT writes by taking
                      EX locks.

    * coherency=buffered, allow concurrent O_DIRECT writes
                          without EX lock among nodes, which
                          gains high performance at risk of
                          getting stale data on other nodes.

Signed-off-by: Tristan Ye <tristan.ye@oracle.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>
This commit is contained in:
Tristan Ye
2010-10-11 16:46:39 +08:00
committed by Joel Becker
parent 75d9bbc738
commit 7bdb0d18bf
4 changed files with 52 additions and 2 deletions
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7
Documentation/filesystems/ocfs2.txt
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@ -87,3 +87,10 @@ dir_resv_level= (*) By default, directory reservations will scale with file
reservations - users should rarely need to change this
value. If allocation reservations are turned off, this
option will have no effect.
coherency=full (*) Disallow concurrent O_DIRECT writes, cluster inode
lock will be taken to force other nodes drop cache,
therefore full cluster coherency is guaranteed even
for O_DIRECT writes.
coherency=buffered Allow concurrent O_DIRECT writes without EX lock among
nodes, which gains high performance at risk of getting
stale data on other nodes.