Messages in this thread | | | Date | Tue, 23 Jun 2009 08:01:37 -0700 | From | Andrew Morton <> | Subject | Re: merging the per-bdi writeback patchset |
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On Tue, 23 Jun 2009 10:55:05 +0200 Jens Axboe <jens.axboe@oracle.com> wrote:
> 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 :-)
Yeah, sorry.
> > 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.
That's a bug, isn't it? This
/* Is another pdflush already flushing this queue? */ if (current_is_pdflush() && !writeback_acquire(bdi)) break;
isn't working.
> 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.
hm, true. 100% starved, or just "slowed down"? The latter I trust - otherwise there are still failure modes?
> > 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.
OK.
How many kernel threads do the 1000-spindle people end up with?
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