Re: [patch v3] mm, page_alloc: reintroduce page allocation stall warning

[Michal Hocko]

On Mon 30-03-26 18:20:57, David Rientjes wrote:
> Previously, we had warnings when a single page allocation took longer
> than reasonably expected.  This was introduced in commit 63f53dea0c98
> ("mm: warn about allocations which stall for too long").
> 
> The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
> warn about allocations which stall for too long") because it was possible
> to generate memory pressure that would effectively stall further progress
> through printk execution.
> 
> Page allocation stalls in excess of 10 seconds are always useful to debug
> because they can result in severe userspace unresponsiveness.  Adding
> this artifact can be used to correlate with userspace going out to lunch
> and to understand the state of memory at the time.
> 
> There should be a reasonable expectation that this warning will never
> trigger given it is very passive, it will only be emitted when a page
> allocation takes longer than 10 seconds.  If it does trigger, this
> reveals an issue that should be fixed: a single page allocation should
> never loop for more than 10 seconds without oom killing to make memory
> available.
> 
> Unlike the original implementation, this implementation only reports
> stalls once for the system every 10 seconds.  Otherwise, many concurrent
> reclaimers could spam the kernel log unnecessarily.  Stalls are only
> reported when calling into direct reclaim.
> 
> Acked-by: Vlastimil Babka (SUSE) <vbabka@xxxxxxxxxx>
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>

OK, let's go with this and tune it up as we find a need in the future.
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Thanks!
-- 
Michal Hocko
SUSE Labs