Messages in this thread | | | Date | Sat, 30 May 2020 00:04:01 +0800 | From | Feng Tang <> | Subject | Re: [PATCH 0/3] make vm_committed_as_batch aware of vm overcommit policy |
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On Fri, May 29, 2020 at 08:50:25AM -0700, Andi Kleen wrote: > > > > ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); > > - if (ret == 0 && write) > > + if (ret == 0 && write) { > > + if (sysctl_overcommit_memory == OVERCOMMIT_NEVER) > > + schedule_on_each_cpu(sync_overcommit_as); > > The schedule is not atomic. > There's still a race window here over all the CPUs where the WARN_ON could > happen because you change the global first.
The re-computing of batch number comes after this sync, so at this point the batch is still the bigger one, and won't trigger the warning.
> Probably you would need another global that says "i'm currently changing > the mode" and then skip the WARN_ON in that window. Maybe a sequence lock. > > Seems all overkill to me. Better to kill the warning.
Yes, the cost is high, schedule_on_each_cpu is labeled as "very slow" in the code comments.
Thanks, Feng
> > -Andi
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