lkml.org 
[lkml]   [2011]   [May]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH 3/3] mm: slub: Default slub_max_order to 0
    From
    Date
    On Thu, 2011-05-12 at 22:29 +0200, Johannes Weiner wrote:
    > On Thu, May 12, 2011 at 03:04:12PM -0500, James Bottomley wrote:
    > > On Thu, 2011-05-12 at 14:44 -0500, James Bottomley wrote:
    > > > On Thu, 2011-05-12 at 13:37 -0500, James Bottomley wrote:
    > > > > On Thu, 2011-05-12 at 18:55 +0300, Pekka Enberg wrote:
    > > > > > On Thu, 2011-05-12 at 10:43 -0500, James Bottomley wrote:
    > > > > > > However, since you admit even you see problems, let's concentrate on
    > > > > > > fixing them rather than recriminations?
    > > > > >
    > > > > > Yes, please. So does dropping max_order to 1 help?
    > > > > > PAGE_ALLOC_COSTLY_ORDER is set to 3 in 2.6.39-rc7.
    > > > >
    > > > > Just booting with max_slab_order=1 (and none of the other patches
    > > > > applied) I can still get the machine to go into kswapd at 99%, so it
    > > > > doesn't seem to make much of a difference.
    > > > >
    > > > > Do you want me to try with the other two patches and max_slab_order=1?
    > > >
    > > > OK, so patches 1 + 2 plus setting slub_max_order=1 still manages to
    > > > trigger the problem (kswapd spinning at 99%). This is still with
    > > > PREEMPT; it's possible that non-PREEMPT might be better, so I'll try
    > > > patches 1+2+3 with PREEMPT just to see if the perturbation is caused by
    > > > it.
    > >
    > > Confirmed, I'm afraid ... I can trigger the problem with all three
    > > patches under PREEMPT. It's not a hang this time, it's just kswapd
    > > taking 100% system time on 1 CPU and it won't calm down after I unload
    > > the system.
    >
    > That is kind of expected, though. If one CPU is busy with a streaming
    > IO load generating new pages, kswapd is busy reclaiming the old ones
    > so that the generator does not have to do the reclaim itself.
    >
    > By unload, do you mean stopping the generator?

    Correct.

    > And if so, how quickly
    > after you stop the generator does kswapd go back to sleep?

    It doesn't. At least not on its own; the CPU stays pegged. If I start
    other work (like a kernel compile), then sometimes it does go back to
    nothing.

    I'm speculating that this is the hang case for non-PREEMPT.

    James




    \
     
     \ /
      Last update: 2011-05-12 22:35    [W:0.023 / U:29.316 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site