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Date: Wed, 23 Feb 2022 23:10:02 -0800 From: Shakeel Butt <shakeelb@...gle.com> To: Suren Baghdasaryan <surenb@...gle.com> Cc: akpm@...ux-foundation.org, hannes@...xchg.org, mhocko@...e.com, pmladek@...e.com, peterz@...radead.org, guro@...com, minchan@...nel.org, timmurray@...gle.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org, kernel-team@...roid.com Subject: Re: [PATCH v3 1/1] mm: count time in drain_all_pages during direct reclaim as memory pressure On Wed, Feb 23, 2022 at 11:48:12AM -0800, Suren Baghdasaryan wrote: > When page allocation in direct reclaim path fails, the system will > make one attempt to shrink per-cpu page lists and free pages from > high alloc reserves. Draining per-cpu pages into buddy allocator can > be a very slow operation because it's done using workqueues and the > task in direct reclaim waits for all of them to finish before > proceeding. Currently this time is not accounted as psi memory stall. > While testing mobile devices under extreme memory pressure, when > allocations are failing during direct reclaim, we notices that psi > events which would be expected in such conditions were not triggered. > After profiling these cases it was determined that the reason for > missing psi events was that a big chunk of time spent in direct > reclaim is not accounted as memory stall, therefore psi would not > reach the levels at which an event is generated. Further investigation > revealed that the bulk of that unaccounted time was spent inside > drain_all_pages call. > A typical captured case when drain_all_pages path gets activated: > __alloc_pages_slowpath took 44.644.613ns > __perform_reclaim took 751.668ns (1.7%) > drain_all_pages took 43.887.167ns (98.3%) > PSI in this case records the time spent in __perform_reclaim but > ignores drain_all_pages, IOW it misses 98.3% of the time spent in > __alloc_pages_slowpath. > Annotate __alloc_pages_direct_reclaim in its entirety so that delays > from handling page allocation failure in the direct reclaim path are > accounted as memory stall. > Reported-by: Tim Murray <timmurray@...gle.com> > Signed-off-by: Suren Baghdasaryan <surenb@...gle.com> > Acked-by: Johannes Weiner <hannes@...xchg.org> Reviewed-by: Shakeel Butt <shakeelb@...gle.com>
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