Messages in this thread | | | Date | Tue, 3 Aug 2021 13:44:02 -0300 | From | Marcelo Tosatti <> | Subject | Re: [patch 2/4] task isolation: sync vmstats on return to userspace |
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On Tue, Aug 03, 2021 at 05:13:03PM +0200, nsaenzju@redhat.com wrote: > On Fri, 2021-07-30 at 17:18 -0300, Marcelo Tosatti wrote: > > The logic to disable vmstat worker thread, when entering > > nohz full, does not cover all scenarios. For example, it is possible > > for the following to happen: > > > > 1) enter nohz_full, which calls refresh_cpu_vm_stats, syncing the stats. > > 2) app runs mlock, which increases counters for mlock'ed pages. > > 3) start -RT loop > > > > Since refresh_cpu_vm_stats from nohz_full logic can happen _before_ > > the mlock, vmstat shepherd can restart vmstat worker thread on > > the CPU in question. > > > > To fix this, use the task isolation prctl interface to quiesce > > deferred actions when returning to userspace. > > Even though this is mostly targeted at nohz_full users, I believe I haven't > seen anything in this series that forces the feature to be run on nohz_full > CPUs (this is a good thing IMO).
I don't think there is such a dependency either.
> So, I'd suggest to reword the patch > description so it doesn't imply nohz_full is necessary to use this.
Its describing a fact from nohz_full where it can't guarantee entering userspace with vmstat turned off (which is a reply to Christopher's earlier comment that "this should just work with nohz_full and logic to shutdown the vmstat delayed work timer").
Will add a comment to make it explicit that the series does not depend on nohz_full.
Thanks.
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