Messages in this thread | | | Date | Fri, 27 Mar 2009 22:38:06 +0100 | From | Jan Kara <> | Subject | Re: ext3 IO latency measurements (was: Linux 2.6.29) |
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On Thu 26-03-09 15:57:25, Andrew Morton wrote: > On Thu, 26 Mar 2009 15:39:53 -0700 (PDT) Linus Torvalds <torvalds@linux-foundation.org> wrote: > > > On Thu, 26 Mar 2009, Jan Kara wrote: > > > > > > Reads are measurably better with the patch - the test with cat you > > > describe below took ~0.5s per file without the patch and always less than > > > 0.02s with the patch. So it seems to help something. > > > > That would seem to be a _huge_ improvement. > > It's strange that we still don't have an ext3_writepages(). Open a > transaction, do a large pile of writes, close the transaction again. > We don't even have a data=writeback writepages() implementation, which > should be fairly simple. Doable but not fairly simple ;) Firstly you have to restart a transaction when you've used up all the credits you originally started with (easy), secondly ext3 uses lock order PageLock -> "transaction start" which is unusable for the scheme you suggest. So we'd have to revert that - which needs larger audit of our locking scheme and that's probably the reason why noone has done it yet.
> Bizarre. > > Mingming had a shot at it a few years ago and I think Badari did as > well, but I guess it didn't work out. > > Falling back to generic_writepages() on our main local fs is a bit lame.
Honza -- Jan Kara <jack@suse.cz> SUSE Labs, CR
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