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authorTheodore Ts'o <tytso@mit.edu>2009-01-03 20:27:38 -0500
committerTheodore Ts'o <tytso@mit.edu>2009-01-03 20:27:38 -0500
commit30773840c19cea60dcef39545960d541b1ac1cf8 (patch)
treef220a2dce451a40dc7264e8fd70c77c5a3908873 /Documentation/filesystems/ext4.txt
parentd7cfa4684d82f58e5d7cb73b8a3c88c169937f25 (diff)
ext4: add fsync batch tuning knobs
Add new mount options, min_batch_time and max_batch_time, which controls how long the jbd2 layer should wait for additional filesystem operations to get batched with a synchronous write transaction. Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Diffstat (limited to 'Documentation/filesystems/ext4.txt')
-rw-r--r--Documentation/filesystems/ext4.txt29
1 files changed, 29 insertions, 0 deletions
diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt
index f75ab101c00..e3fcbea3ec8 100644
--- a/Documentation/filesystems/ext4.txt
+++ b/Documentation/filesystems/ext4.txt
@@ -283,6 +283,35 @@ delalloc (*) Deferring block allocation until write-out time.
nodelalloc Disable delayed allocation. Blocks are allocation
when data is copied from user to page cache.
+max_batch_time=usec Maximum amount of time ext4 should wait for
+ additional filesystem operations to be batch
+ together with a synchronous write operation.
+ Since a synchronous write operation is going to
+ force a commit and then a wait for the I/O
+ complete, it doesn't cost much, and can be a
+ huge throughput win, we wait for a small amount
+ of time to see if any other transactions can
+ piggyback on the synchronous write. The
+ algorithm used is designed to automatically tune
+ for the speed of the disk, by measuring the
+ amount of time (on average) that it takes to
+ finish committing a transaction. Call this time
+ the "commit time". If the time that the
+ transactoin has been running is less than the
+ commit time, ext4 will try sleeping for the
+ commit time to see if other operations will join
+ the transaction. The commit time is capped by
+ the max_batch_time, which defaults to 15000us
+ (15ms). This optimization can be turned off
+ entirely by setting max_batch_time to 0.
+
+min_batch_time=usec This parameter sets the commit time (as
+ described above) to be at least min_batch_time.
+ It defaults to zero microseconds. Increasing
+ this parameter may improve the throughput of
+ multi-threaded, synchronous workloads on very
+ fast disks, at the cost of increasing latency.
+
Data Mode
=========
There are 3 different data modes: