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Fri, 07 Jan 2022 15:36:15 -0800 (PST) Date: Fri, 7 Jan 2022 16:36:11 -0700 From: Yu Zhao To: Michal Hocko Cc: Andrew Morton , Linus Torvalds , Andi Kleen , Catalin Marinas , Dave Hansen , Hillf Danton , Jens Axboe , Jesse Barnes , Johannes Weiner , Jonathan Corbet , Matthew Wilcox , Mel Gorman , Michael Larabel , Rik van Riel , Vlastimil Babka , Will Deacon , Ying Huang , linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, page-reclaim@google.com, x86@kernel.org, Konstantin Kharlamov Subject: Re: [PATCH v6 6/9] mm: multigenerational lru: aging Message-ID: References: <20220104202227.2903605-1-yuzhao@google.com> <20220104202227.2903605-7-yuzhao@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=KVMWEcwA; spf=pass (imf19.hostedemail.com: domain of yuzhao@google.com designates 209.85.166.44 as permitted sender) smtp.mailfrom=yuzhao@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspamd-Queue-Id: 3FC971A0002 X-Stat-Signature: abosw8cit95twbwzt3bkjem59nsh8sqx X-Rspamd-Server: rspam04 X-HE-Tag: 1641598576-223930 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 Fri, Jan 07, 2022 at 02:11:29PM +0100, Michal Hocko wrote: > On Tue 04-01-22 13:22:25, Yu Zhao wrote: > [...] > > +static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_control *sc) > > +{ > > + struct mem_cgroup *memcg; > > + bool success = false; > > + unsigned long min_ttl = READ_ONCE(lru_gen_min_ttl); > > + > > + VM_BUG_ON(!current_is_kswapd()); > > + > > + current->reclaim_state->mm_walk = &pgdat->mm_walk; > > + > > + memcg = mem_cgroup_iter(NULL, NULL, NULL); > > + do { > > + struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat); > > + > > + if (age_lruvec(lruvec, sc, min_ttl)) > > + success = true; > > + > > + cond_resched(); > > + } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL))); > > + > > + if (!success && mutex_trylock(&oom_lock)) { > > + struct oom_control oc = { > > + .gfp_mask = sc->gfp_mask, > > + .order = sc->order, > > + }; > > + > > + if (!oom_reaping_in_progress()) > > + out_of_memory(&oc); > > + > > + mutex_unlock(&oom_lock); > > + } > > Why do you need to trigger oom killer from this path? Why cannot you > rely on the page allocator to do that like we do now? This is per desktop users' (repeated) requests. The can't tolerate thrashing as servers do because of UI lags; and they usually don't have fancy tools like oomd. Related discussions I saw: https://github.com/zen-kernel/zen-kernel/issues/218 https://lore.kernel.org/lkml/20101028191523.GA14972@google.com/ https://lore.kernel.org/lkml/20211213051521.21f02dd2@mail.inbox.lv/ https://lore.kernel.org/lkml/54C2C89C.8080002@gmail.com/ https://lore.kernel.org/lkml/d9802b6a-949b-b327-c4a6-3dbca485ec20@gmx.com/ >From patch 8: Personal computers ------------------ :Thrashing prevention: Write ``N`` to ``/sys/kernel/mm/lru_gen/min_ttl_ms`` to prevent the working set of ``N`` milliseconds from getting evicted. The OOM killer is invoked if this working set can't be kept in memory. Based on the average human detectable lag (~100ms), ``N=1000`` usually eliminates intolerable lags due to thrashing. Larger values like ``N=3000`` make lags less noticeable at the cost of more OOM kills.