Messages in this thread | | | Date | Tue, 23 Jun 2009 10:55:05 +0200 | From | Jens Axboe <> | Subject | Re: merging the per-bdi writeback patchset |
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On Tue, Jun 23 2009, Andrew Morton wrote: > On Tue, 23 Jun 2009 10:11:56 +0200 Jens Axboe <jens.axboe@oracle.com> wrote: > > > Things are looking good for this patchset and it's been in -next for > > almost a week without any reports of problems. So I'd like to merge it > > for 2.6.31 if at all possible. Any objections? > > erk. I was rather expecting I'd have time to have a look at it all.
OK, we can wait if we have to, just trying to avoid having to keep this fresh for one full cycle. I have posted this patchset 11 times though over months, so it's not like it's a new piece of work :-)
> It's unclear to me actually _why_ the performance changes which were > observed have actually occurred. In fact it's a bit unclear (to me) > why the patchset was written and what it sets out to achieve :(
It started out trying to get rid of the pdflush uneven writeout. If you look at various pdflush intensive workloads, even on a single disk you often have 5 or more pdflush threads working the same device. It's just not optimal. Another issue was starvation with request allocation. Given that pdflush does non-blocking writes (it has to, by design), pdflush can potentially be starved if someone else is working the device.
> A long time ago the XFS guys (Dave Chinner iirc) said that XFS needs > more than one thread per device to keep the device saturated. Did that > get addressed?
It supports up to 32-threads per device, but Chinner et all have been silent. So the support is there and there's a super_operations->inode_get_wb() to map a dirty inode to a writeback device. Nobody is doing that yet though.
> (kthread_run() returns an ERR_PTR() on error, btw - not NULL.)
Oh thanks, will fix that up.
-- Jens Axboe
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