Re: [RFC] ext3: per-process soft-syncing data=ordered mode

[Jan Kara]

> Greetings!
> 
> data=ordered mode has proven reliable over the years, and it does this by 
> ordering filedata flushes before metadata flushes.  But this sometimes 
> causes contention in the order of a 10x slowdown for certain apps, either 
> due to the misuse of fsync or due to inherent behaviour like db's, as well 
> as inherent starvation issues exposed by the data=ordered mode.
> 
> data=writeback mode alleviates data=order mode slowdowns, but only works 
> per-mount and is too dangerous to run as a default mode.
> 
> This RFC proposes to introduce a tunable which allows to disable fsync and 
> changes ordered into writeback writeout on a per-process basis like this:
> 
>       echo 1 > /proc/`pidof process`/softsync
  I guess disabling fsync() was already commented on enough. Regarding
switching to writeback mode on per-process basis - not easily possible
because sometimes data is not written out by the process which stored
them (think of mmaped file). And in case of DB, they use direct-io
anyway most of the time so they don't care about journaling mode anyway.
  But as Diego wrote, there is definitely some room for improvement in
current data=ordered mode so the difference shouldn't be as big in the
end.

								Honza
-- 
Jan Kara <jack@xxxxxxx>
SuSE CR Labs
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/