From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0BC11C433EF for ; Thu, 24 Feb 2022 08:53:15 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 9F5BA8D0003; Thu, 24 Feb 2022 03:53:14 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 9A56B8D0001; Thu, 24 Feb 2022 03:53:14 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8BBB68D0003; Thu, 24 Feb 2022 03:53:14 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.hostedemail.com [64.99.140.25]) by kanga.kvack.org (Postfix) with ESMTP id 7F3BA8D0001 for ; Thu, 24 Feb 2022 03:53:14 -0500 (EST) Received: from smtpin03.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 564B221475 for ; Thu, 24 Feb 2022 08:53:14 +0000 (UTC) X-FDA: 79177059108.03.2D13817 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by imf19.hostedemail.com (Postfix) with ESMTP id 945071A0005 for ; Thu, 24 Feb 2022 08:53:13 +0000 (UTC) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id 757211F39D; Thu, 24 Feb 2022 08:53:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1645692792; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=8C4+gSdHMlHl52I6AqAMZLL28rQul65Dt9Lg29GnGjM=; b=MQpiomIbgDTdVjqGJwF7tPFvgn5lIFIfWTZ9VUzFqhEWYaXMLeshftcyp9ZfkLMLrkjQ68 udJyj4lixfCRfHTXtwUJkKzUMb5mUIhzEdnP0iJ02wUDKP4R/7rUB9U2EKjwH1ynB4+0gU knXl7w5B9i72Rt0X/sQU2D2lMzWFvxA= Received: from suse.cz (unknown [10.100.201.86]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 43E7CA3B99; Thu, 24 Feb 2022 08:53:12 +0000 (UTC) Date: Thu, 24 Feb 2022 09:53:11 +0100 From: Michal Hocko To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, pmladek@suse.com, peterz@infradead.org, guro@fb.com, shakeelb@google.com, minchan@kernel.org, timmurray@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v3 1/1] mm: count time in drain_all_pages during direct reclaim as memory pressure Message-ID: References: <20220223194812.1299646-1-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220223194812.1299646-1-surenb@google.com> X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 945071A0005 X-Rspam-User: Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=MQpiomIb; spf=pass (imf19.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.29 as permitted sender) smtp.mailfrom=mhocko@suse.com; dmarc=pass (policy=quarantine) header.from=suse.com X-Stat-Signature: cyb9m1z9ca4otte4m69763zefuhxfo8m X-HE-Tag: 1645692793-445629 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed 23-02-22 11:48:12, 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%) Although the draining is done in the slow path these numbers suggest that we should really reconsider the use of WQ both for draining and other purposes (like vmstats). > 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 > Signed-off-by: Suren Baghdasaryan > Acked-by: Johannes Weiner Acked-by: Michal Hocko Thanks! > --- > changes in v3: > - Moved psi_memstall_leave after the "out" label > > mm/page_alloc.c | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 3589febc6d31..029bceb79861 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4595,13 +4595,12 @@ __perform_reclaim(gfp_t gfp_mask, unsigned int order, > const struct alloc_context *ac) > { > unsigned int noreclaim_flag; > - unsigned long pflags, progress; > + unsigned long progress; > > cond_resched(); > > /* We now go into synchronous reclaim */ > cpuset_memory_pressure_bump(); > - psi_memstall_enter(&pflags); > fs_reclaim_acquire(gfp_mask); > noreclaim_flag = memalloc_noreclaim_save(); > > @@ -4610,7 +4609,6 @@ __perform_reclaim(gfp_t gfp_mask, unsigned int order, > > memalloc_noreclaim_restore(noreclaim_flag); > fs_reclaim_release(gfp_mask); > - psi_memstall_leave(&pflags); > > cond_resched(); > > @@ -4624,11 +4622,13 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order, > unsigned long *did_some_progress) > { > struct page *page = NULL; > + unsigned long pflags; > bool drained = false; > > + psi_memstall_enter(&pflags); > *did_some_progress = __perform_reclaim(gfp_mask, order, ac); > if (unlikely(!(*did_some_progress))) > - return NULL; > + goto out; > > retry: > page = get_page_from_freelist(gfp_mask, order, alloc_flags, ac); > @@ -4644,6 +4644,8 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order, > drained = true; > goto retry; > } > +out: > + psi_memstall_leave(&pflags); > > return page; > } > -- > 2.35.1.473.g83b2b277ed-goog -- Michal Hocko SUSE Labs