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SubjectRe: swsusp performance problems in 2.6.15-rc3-mm1
On Tue, Dec 06, 2005 at 12:05:04AM +0100, Rafael J. Wysocki wrote:
> On Monday, 5 December 2005 09:19, Andy Isaacson wrote:
> > On recent kernels such as 2.6.14-rc2-mm1, a swsusp of my laptop (1.25
> > GB, P4M 1.4 GHz) was a pretty fast process; freeing memory took about 3
> > seconds or less,
> It took much more time on my box, but I won't discuss with your
> experience. ;-)

I may be misremembering, it didn't seem important at the time. Less
than 10 seconds, anyways.

> > Certainly there's a tradeoff to be made, and I'm glad to lose the slow
> > re-paging after resume, but I'm hoping that some kind of improvement can
> > be made in the suspend/resume time.
> Yes, there is a tradeoff. Till now, we have used the simplistic approach
> based on freeing as much memory as possible before suspend. Now, we
> are freeing only as much memory as necessary, which is on the other
> end of the scale, so to speak. There are a whole lot of possibilities in
> between, and there's a question which one is the best. Frankly, I'm afraid
> the answer is very system-dependent.

If you wanted to compute "What's the absolute perfect 99.9999th
percentile amount to free", yes, that would be impossibly

But some kind of rule of thumb should get good results in most cases,
and it should be easy enough to add a knob for people who have
particular requirements.

> If you want a quick solution, you can get back to the previous behavior by
> commenting out the definition of FAST_FREE in kernel/power/power.h.

That's boring. :) The current behavior isn't bad enough to force me

> Alternatively, you can increase the value of PAGES_FOR_IO, defined
> in include/linux/suspend.h. To see any effect, you'll probably have to
> increase it by tens of thousands, but please note the box may be unable
> to suspend if it's too great (if you try this anyway, please let me know what
> number seems to be the best to you).
> Also, I can create a patch to improve this a bit, if you promise to help
> test/debug it. ;-)

I'll play with this a bit tonight but I'd love to see a patch that makes
it a tunable. Rebooting my laptop is sloooow and annoying (due to slow
startup scripts and losing all my state), but trying various suspend
settings sounds like a fun experiment.

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