Messages in this thread Patch in this message | | | Subject | Re: writeout stalls in current -git | From | Peter Zijlstra <> | Date | Tue, 06 Nov 2007 11:20:41 +0100 |
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On Mon, 2007-11-05 at 15:57 -0800, Andrew Morton wrote:
> > > Subject: mm: speed up writeback ramp-up on clean systems > > > > > > We allow violation of bdi limits if there is a lot of room on the > > > system. Once we hit half the total limit we start enforcing bdi limits > > > and bdi ramp-up should happen. Doing it this way avoids many small > > > writeouts on an otherwise idle system and should also speed up the > > > ramp-up. > > Given the problems we're having in there I'm a bit reluctant to go tossing > hastily put together and inadequately tested stuff onto the fire. And > that's what this patch looks like to me.
Not really hastily, I think it was written before the stuff hit mainline. Inadequately tested, perhaps, its been in my and probably Wu's kernels for a while. Granted that's not a lot of testing in the face of those who have problems atm.
> Wanna convince me otherwise?
I'm perfectly happy with this patch earning its credits in -mm for a while and maybe going in around -rc4 or something like that (hoping that by then we've fixed these nagging issues).
Another patch I did come up with yesterday - not driven by any problems in that area - could perhaps join this one on that path:
--- Subject: mm: bdi: tweak task dirty penalty
Penalizing heavy dirtiers with 1/8-th the total dirty limit might be rather excessive on large memory machines. Use sqrt to scale it sub-linearly.
Update the comment while we're there.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> --- mm/page-writeback.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)
Index: linux-2.6-2/mm/page-writeback.c =================================================================== --- linux-2.6-2.orig/mm/page-writeback.c +++ linux-2.6-2/mm/page-writeback.c @@ -213,17 +213,21 @@ static inline void task_dirties_fraction } /* - * scale the dirty limit + * Task specific dirty limit: * - * task specific dirty limit: + * dirty -= 8 * sqrt(dirty) * p_{t} * - * dirty -= (dirty/8) * p_{t} + * Penalize tasks that dirty a lot of pages by lowering their dirty limit. This + * avoids infrequent dirtiers from getting stuck in this other guys dirty + * pages. + * + * Use a sub-linear function to scale the penalty, we only need a little room. */ void task_dirty_limit(struct task_struct *tsk, long *pdirty) { long numerator, denominator; long dirty = *pdirty; - u64 inv = dirty >> 3; + u64 inv = 8*int_sqrt(dirty); task_dirties_fraction(tsk, &numerator, &denominator); inv *= numerator;
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