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 EEDCDC433EF for ; Tue, 11 Jan 2022 09:00:36 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 77F716B0072; Tue, 11 Jan 2022 04:00:36 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 70AB46B0073; Tue, 11 Jan 2022 04:00:36 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5AA0B6B0074; Tue, 11 Jan 2022 04:00:36 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0095.hostedemail.com [216.40.44.95]) by kanga.kvack.org (Postfix) with ESMTP id 4A9846B0072 for ; Tue, 11 Jan 2022 04:00:36 -0500 (EST) Received: from smtpin27.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 1350495C88 for ; Tue, 11 Jan 2022 09:00:36 +0000 (UTC) X-FDA: 79017410472.27.6BA4A8E Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by imf09.hostedemail.com (Postfix) with ESMTP id 50705140014 for ; Tue, 11 Jan 2022 09:00:35 +0000 (UTC) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id 1CD5A1F3B6; Tue, 11 Jan 2022 09:00:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1641891634; 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=OeasfAigrOwxNyBh17klLqWDReCRAIT8+9bALhOBBTE=; b=OMEOsmUPz8Sg5EGy0PNoyTTlWBHkVa2PxtC09u3JHkWldsYJD3LDsOF2LQXxRkUQ+wrIz9 kcASeAyImPhvK10QPGGJBnFhD4+6Ifeni3fz+rJutCz7kPryrVDu9fMuWjvffV0B/2cRYu QcGlA6B7IXEkYO+V2VC7xQyW7LQxBQ4= 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 49F73A3B9B; Tue, 11 Jan 2022 09:00:33 +0000 (UTC) Date: Tue, 11 Jan 2022 10:00:32 +0100 From: Michal Hocko To: Yu Zhao 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: X-Stat-Signature: tznrqxu9jo1dhh6huztthkgjizywaqpe Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=OMEOsmUP; dmarc=pass (policy=quarantine) header.from=suse.com; spf=pass (imf09.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.29 as permitted sender) smtp.mailfrom=mhocko@suse.com X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 50705140014 X-HE-Tag: 1641891635-489973 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 Mon 10-01-22 18:18:55, Yu Zhao wrote: > On Mon, Jan 10, 2022 at 04:35:46PM +0100, Michal Hocko wrote: > > On Fri 07-01-22 16:36:11, Yu Zhao wrote: > > > 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/ > > > > I do not really see any arguments why an userspace based trashing > > detection cannot be used for those. Could you clarify? > > It definitely can be done. But who is going to do it for every distro > and all individual users? AFAIK, not a single distro provides such a > solution for desktop/laptop/phone users. If existing interfaces provides sufficient information to make those calls then I would definitely prefer a userspace solution. > And also there is the theoretical question how reliable a userspace > solution can be. What if this usespace solution itself gets stuck in > the direct reclaim path. I'm sure if nobody has done some search to > prove or debunk it. I have to confess I haven't checked oomd or other solutions but with a sufficient care (all the code mlocked in + no allocations done while collecting data) I believe this should be achieveable. > In addition, what exactly PSI values should be used on different > models of consumer electronics? Nobody knows. We have a team working > on this and we haven't figured it out for all our Chromebook models. I believe this is a matter of tuning for a specific deployment. We do not have only psi but also refault counters that can be used. > As Andrew said, "a blunt instrument like this would be useful". > https://lore.kernel.org/lkml/20211202135824.33d2421bf5116801cfa2040d@linux-foundation.org/ > > I'd like to have less code in kernel too, but I've learned never to > walk over users. If I remove this and they come after me asking why, > I'd have a hard time convincing them. > > > Also my question was pointing to why out_of_memory is called from the > > reclaim rather than the allocator (memcg charging path). It is the > > caller of the reclaim to control different reclaim strategies and tell > > when all the hopes are lost and the oom killer should be invoked. This > > allows for a different policies at the allocator level and this change > > will break that AFAICS. E.g. what if the underlying allocation context > > is __GFP_NORETRY? > > This is called in kswapd only, and by default (min_ttl=0) it doesn't > do anything. So __GFP_NORETRY doesn't apply. My bad. I must have got lost when traversing the code but I can see you are enforcing that by a VM_BUG_ON. So the limited scope reclaim is not a problem indeed. > The question would be > more along the lines of long-term ABI support. > > And I'll add the following comments, if you think we can keep this > logic: > OOM kill if every generation from all memcgs is younger than min_ttl. > Another theoretical possibility is all memcgs are either below min or > ineligible at priority 0, but this isn't the main goal. > > (Please read my reply at the bottom to decide whether we should keep > it or not. Thanks.) > > > > >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. > > > > This is a very good example of something that should be a self contained > > patch with its own justification. > > Consider it done. > > > TBH it is really not all that clear to > > me that we want to provide any user visible knob to control OOM behavior > > based on a time based QoS. > > Agreed, and it didn't exist until v4, i.e., after I was demanded to > provide it for several times. > > For example: > https://github.com/zen-kernel/zen-kernel/issues/223 > > And another example: > Your Multigenerational LRU patchset is pretty complex and > effective, but does not eliminate thrashing condition fully on an > old PCs with slow HDD. > > I'm kindly asking you to cooperate with hakavlad if it's possible > and maybe re-implement parts of le9 patch in your patchset wherever > acceptable, as they are quite similar in the core concept. > > This is excerpt of an email from iam@valdikss.org.ru, and he has > posted demo videos in this discussion: > https://lore.kernel.org/lkml/2dc51fc8-f14e-17ed-a8c6-0ec70423bf54@valdikss.org.ru/ That is all an interesting feedback but we should be really craful about ABI constrains and future maintainability of the knob. I still stand behind my statement that kernel should implement such features only if it is clear that we cannot really implement a similar logic in the userspace. -- Michal Hocko SUSE Labs