Messages in this thread | | | Date | Wed, 20 Jun 2007 11:20:59 +0200 | From | Jens Axboe <> | Subject | Re: Change in default vm_dirty_ratio |
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On Wed, Jun 20 2007, Peter Zijlstra wrote: > On Wed, 2007-06-20 at 11:14 +0200, Jens Axboe wrote: > > On Wed, Jun 20 2007, Andrew Morton wrote: > > > Perhaps our queues are too long - if the VFS _does_ back off, it'll take > > > some time for that to have an effect. > > > > > > Perhaps the fact that the queue size knows nothing about the _size_ of the > > > requests in the queue is a problem. > > > > It's complicated, the size may not matter a lot. 128 sequential 512kb IO > > may complete faster than 128 random 4kb IO's. > > Yes, is there any way a queue could be limited to a certain amount of > 'completion time' ?
Not easily, we'd need some sort of disk profile for that to be remotely reliable.
> > > Back away even further here. > > > > > > What user-visible problem(s) are we attemping to fix? > > > > I'd like innocent-app-doing-little-write-or-fsync not being stalled by > > big-bad-app-doing-lots-of-dirtying. > > Could you please try this per BDI dirty limit -v7 patch series, the very > last patch tries to address this by taking the per task dirty rate into > account.
Yeah, I've been watching your patchset with interesting. Hope it'll get merged some time soon, I think it's a real problem.
> Although, on the fsync, ext3 seems to want to do a global fsync, which > will still make the experience suck. :-(
Yeah well, extX sucks on many levels :-)
-- Jens Axboe
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