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[98.15.154.102]) by smtp.gmail.com with ESMTPSA id f207sm210953qke.22.2022.02.23.10.54.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 23 Feb 2022 10:54:57 -0800 (PST) Date: Wed, 23 Feb 2022 13:54:56 -0500 From: Johannes Weiner To: Suren Baghdasaryan Cc: Minchan Kim , akpm@linux-foundation.org, mhocko@suse.com, peterz@infradead.org, guro@fb.com, shakeelb@google.com, timmurray@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH 1/1] mm: count time in drain_all_pages during direct reclaim as memory pressure Message-ID: References: <20220219174940.2570901-1-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Feb 20, 2022 at 08:52:38AM -0800, Suren Baghdasaryan wrote: > On Sat, Feb 19, 2022 at 4:40 PM Minchan Kim wrote: > > > > On Sat, Feb 19, 2022 at 09:49:40AM -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 > > > > Yes, drain_all_pages is serious slow(100ms - 150ms on Android) > > especially when CPUs are fully packed. It was also spotted in CMA > > allocation even when there was on no memory pressure. > > Thanks for the input, Minchan! > In my tests I've seen 50-60ms delays in a single drain_all_pages but I > can imagine there are cases worse than these. > > > > > > proceeding. Currently this time is not accounted as psi memory stall. > > > > Good spot. > > > > > > > > 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. > > > > > > Annotate drain_all_pages and unreserve_highatomic_pageblock during > > > page allocation failure in the direct reclaim path so that delays > > > caused by these calls are accounted as memory stall. > > > > > > Reported-by: Tim Murray > > > Signed-off-by: Suren Baghdasaryan > > > --- > > > mm/page_alloc.c | 4 ++++ > > > 1 file changed, 4 insertions(+) > > > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > > index 3589febc6d31..7fd0d392b39b 100644 > > > --- a/mm/page_alloc.c > > > +++ b/mm/page_alloc.c > > > @@ -4639,8 +4639,12 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order, > > > * Shrink them and try again > > > */ > > > if (!page && !drained) { > > > + unsigned long pflags; > > > + > > > + psi_memstall_enter(&pflags); > > > unreserve_highatomic_pageblock(ac, false); > > > drain_all_pages(NULL); > > > + psi_memstall_leave(&pflags); > > > > Instead of annotating the specific drain_all_pages, how about > > moving the annotation from __perform_reclaim to > > __alloc_pages_direct_reclaim? > > I'm fine with that approach too. Let's wait for Johannes' input before > I make any changes. I think the change makes sense, even if the workqueue fix speeds up the drain. I agree with Minchan about moving the annotation upward. With it moved, please feel free to add Acked-by: Johannes Weiner