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ext4: clarify impact of 'commit' mount option

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The description of 'commit' mount option dates back to ext3 times.
Update the description to match current meaning for ext4.

Reported-by: Paul Richards <paul.richards@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20191218111210.14161-1-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Jan Kara 2019-12-18 12:12:10 +01:00 committed by Theodore Ts'o
parent 68d7b2d838
commit 23f6b02405
1 changed files with 11 additions and 8 deletions
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19
Documentation/admin-guide/ext4.rst
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@ -181,14 +181,17 @@ When mounting an ext4 filesystem, the following option are accepted:
system after its metadata has been committed to the journal.
commit=nrsec (*)
Ext4 can be told to sync all its data and metadata every 'nrsec'
seconds. The default value is 5 seconds. This means that if you lose
your power, you will lose as much as the latest 5 seconds of work (your
filesystem will not be damaged though, thanks to the journaling). This
default value (or any low value) will hurt performance, but it's good
for data-safety. Setting it to 0 will have the same effect as leaving
it at the default (5 seconds). Setting it to very large values will
improve performance.
This setting limits the maximum age of the running transaction to
'nrsec' seconds. The default value is 5 seconds. This means that if
you lose your power, you will lose as much as the latest 5 seconds of
metadata changes (your filesystem will not be damaged though, thanks
to the journaling). This default value (or any low value) will hurt
performance, but it's good for data-safety. Setting it to 0 will have
the same effect as leaving it at the default (5 seconds). Setting it
to very large values will improve performance. Note that due to
delayed allocation even older data can be lost on power failure since
writeback of those data begins only after time set in
/proc/sys/vm/dirty_expire_centisecs.
barrier=<0|1(*)>, barrier(*), nobarrier
This enables/disables the use of write barriers in the jbd code.