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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
    system-dependent.

    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
    back.

    > 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.

    -andy
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