Messages in this thread | | | Date | Thu, 22 Jan 2015 16:16:20 +0100 | From | Vlastimil Babka <> | Subject | Re: [PATCH v2] mm: vmscan: fix the page state calculation in too_many_isolated |
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On 01/21/2015 03:39 PM, Michal Hocko wrote: > On Mon 19-01-15 09:57:08, Vinayak Menon wrote: >> On 01/18/2015 01:18 AM, Christoph Lameter wrote: >>> On Sat, 17 Jan 2015, Vinayak Menon wrote: >>> >>>> which had not updated the vmstat_diff. This CPU was in idle for around 30 >>>> secs. When I looked at the tvec base for this CPU, the timer associated with >>>> vmstat_update had its expiry time less than current jiffies. This timer had >>>> its deferrable flag set, and was tied to the next non-deferrable timer in the >>> >>> We can remove the deferrrable flag now since the vmstat threads are only >>> activated as necessary with the recent changes. Looks like this could fix >>> your issue? >>> >> >> Yes, this should fix my issue. > > Does it? Because I would prefer not getting into un-synced state much > more than playing around one specific place which shows the problems > right now. > >> But I think we may need the fix in too_many_isolated, since there can still >> be a delay of few seconds (HZ by default and even more because of reasons >> pointed out by Michal) which will result in reclaimers unnecessarily >> entering congestion_wait. No ? > > I think we can solve this as well. We can stick vmstat_shepherd into a > kernel thread with a loop with the configured timeout and then create a > mask of CPUs which need the update and run vmstat_update from > IPI context (smp_call_function_many). > We would have to drop cond_resched from refresh_cpu_vm_stats of > course. The nr_zones x NR_VM_ZONE_STAT_ITEMS in the IPI context > shouldn't be excessive but I haven't measured that so I might be easily > wrong. > > Anyway, that should work more reliably than the current scheme and > should help to reduce pointless wakeups which the original patchset was > addressing. Or am I missing something?
Maybe to further reduce wakeups, a CPU could check and update its counters before going idle? (unless that already happens)
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