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 EC74FC25B78 for ; Wed, 5 Jun 2024 01:50:33 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 5EAED6B0085; Tue, 4 Jun 2024 21:50:33 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 59B0B6B008A; Tue, 4 Jun 2024 21:50:33 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4623E6B008C; Tue, 4 Jun 2024 21:50:33 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 299AF6B0085 for ; Tue, 4 Jun 2024 21:50:33 -0400 (EDT) Received: from smtpin17.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 9F0CF120F02 for ; Wed, 5 Jun 2024 01:50:32 +0000 (UTC) X-FDA: 82195155504.17.B7E8F7C Received: from invmail4.hynix.com (exvmail4.skhynix.com [166.125.252.92]) by imf22.hostedemail.com (Postfix) with ESMTP id DCDB8C0008 for ; Wed, 5 Jun 2024 01:50:29 +0000 (UTC) Authentication-Results: imf22.hostedemail.com; dkim=none; spf=pass (imf22.hostedemail.com: domain of byungchul@sk.com designates 166.125.252.92 as permitted sender) smtp.mailfrom=byungchul@sk.com; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1717552230; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=q5DhJwupghVJarALt3QcqYhg6Nmh26Jxem6dghOsBJg=; b=VW5kQCWDFP+cjbPCiTs3F8LaKnoqlXpmsxOwJV+sxO5bhw3xYJLJ+sBg9ufyWa+izw6VqP w5HOcMLQWju85KcdaQj1DEqddED4NRcExJwubo41f0kCnXMVtvsTLTGxBWh2varahXGH+F WfEc4NdnQL1S3soCijIKnuJiEn2Vd5k= ARC-Authentication-Results: i=1; imf22.hostedemail.com; dkim=none; spf=pass (imf22.hostedemail.com: domain of byungchul@sk.com designates 166.125.252.92 as permitted sender) smtp.mailfrom=byungchul@sk.com; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1717552230; a=rsa-sha256; cv=none; b=JR8GcUUlK3deObAnLEPWzU5A1ZdSHGBbyXvsLbINAF3dgnLYnnh7/gGM7jrtuta98FgSkp cpaFGSmBsRPw8xJVM1H7NEfDkUESbtSBimG22PD1vdEpeRjdBv7fhihVMgUHbGUdDMtBly mRtkkXRrhtAHflULmc3OF+R1pZoH1yw= X-AuditID: a67dfc5b-d85ff70000001748-33-665fc46277e5 Date: Wed, 5 Jun 2024 10:50:21 +0900 From: Byungchul Park To: "Huang, Ying" Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel_team@skhynix.com, hannes@cmpxchg.org, iamjoonsoo.kim@lge.com, rientjes@google.com Subject: Re: [PATCH v2] mm: let kswapd work again for node that used to be hopeless but may not now Message-ID: <20240605015021.GB75311@system.software.com> References: <20240604072323.10886-1-byungchul@sk.com> <87bk4hcf7h.fsf@yhuang6-desk2.ccr.corp.intel.com> <20240604084533.GA68919@system.software.com> <8734ptccgi.fsf@yhuang6-desk2.ccr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8734ptccgi.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Mutt/1.9.4 (2018-02-28) X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFrrHLMWRmVeSWpSXmKPExsXC9ZZnoW7Skfg0g0Wr5SzmrF/DZrF6k6/F yu5mNovLu+awWdxb85/Vom3JRiaLk7Mmsziwexx+857ZY8GmUo/Fe14yeWz6NIndo+vtFSaP EzN+s3h83iQXwB7FZZOSmpNZllqkb5fAlfHpZjdzQa9KRfuKC8wNjEtkuhg5OSQETCQunX7F 2sXIAWZ/nOgEEmYRUJG4+GMRE4jNJqAucePGT2YQW0RAQ+LTwuXsXYxcHMwCaxkljlxtAesV FkiVOL49AKSGV8BC4u6fy6wgNUICZxglehvWM0EkBCVOznzCAmIzC2hJ3Pj3kgmkl1lAWmL5 Pw6QMKeAnUTvovuMILaogLLEgW3HmUDmSAgcYJP42fmSBeJmSYmDK26wTGAUmIVk7CwkY2ch jF3AyLyKUSgzryw3MTPHRC+jMi+zQi85P3cTIzDUl9X+id7B+OlC8CFGAQ5GJR7eHb/i0oRY E8uKK3MPMUpwMCuJ8PoVx6cJ8aYkVlalFuXHF5XmpBYfYpTmYFES5zX6Vp4iJJCeWJKanZpa kFoEk2Xi4JRqYLSf+HVKXWucWu72S4axYu/eROhN/jqJ+Xrm0UMGE41Ts7TPRL9SXcKtccRf bQ+rObP19n8bZkre0/Zeve9OddmNu+5X+jTe9RoGcnKffFG7Tm2ZZtCxNWWvHL/5KRes87m0 auuU/dGF31mlXnHlbm5Zq6t0aK5CyvXHtVuPWF00OXn00esrzVlKLMUZiYZazEXFiQBD4Uny cQIAAA== X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFjrKLMWRmVeSWpSXmKPExsXC5WfdrJt0JD7N4EiHsMWc9WvYLFZv8rVY 2d3MZnF47klWi8u75rBZ3Fvzn9WibclGJouTsyazOHB4HH7zntljwaZSj8V7XjJ5bPo0id2j 6+0VJo8TM36zeCx+8YHJ4/MmuQCOKC6blNSczLLUIn27BK6MTze7mQt6VSraV1xgbmBcItPF yMEhIWAi8XGiUxcjJweLgIrExR+LmEBsNgF1iRs3fjKD2CICGhKfFi5n72Lk4mAWWMsoceRq CytIr7BAqsTx7QEgNbwCFhJ3/1xmBakREjjDKNHbsJ4JIiEocXLmExYQm1lAS+LGv5dMIL3M AtISy/9xgIQ5BewkehfdZwSxRQWUJQ5sO840gZF3FpLuWUi6ZyF0L2BkXsUokplXlpuYmWOq V5ydUZmXWaGXnJ+7iREYuMtq/0zcwfjlsvshRgEORiUe3h2/4tKEWBPLiitzDzFKcDArifD6 FcenCfGmJFZWpRblxxeV5qQWH2KU5mBREuf1Ck9NEBJITyxJzU5NLUgtgskycXBKNTDe8QvY 4TPl75OMkwuPCDYU2P2eLCR0eDKv6ssjn+Or3cOitbWWBP0pn/zp/o5H7G5TbcIPn7YvcSv1 TGxbvbhS7MIDkR/Kn7emaUxbaCvnU1s6/XjZF+PLB1R4HHQfzzvWvEOVX3h+5VuZPP/VqxJu sSnqOmkYsot3bjsWE9Vi91n58BO2fgUlluKMREMt5qLiRABdMdU8WAIAAA== X-CFilter-Loop: Reflected X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: DCDB8C0008 X-Stat-Signature: iz79q4nz7bdexknj9np5gdzg4hh6tkfh X-HE-Tag: 1717552229-451575 X-HE-Meta: U2FsdGVkX1/fUtFYREXFg4kfoOvs2oy+stAI5o4njQOg4rY37LnhCW/LDBQzZGxzXdqBBrKbds331+LB3WEutSz74BCjxF9HF6f+gJmOsRKmSa4YkqpqVJBBQ8Xds0DNf+KczwpVirN6R4xz6QmXUSGUP09lnuWo0Ctn10a+K5bsl9Gd5JSMizyRxWqlhlCsmwyxdQ1YW4Wdon6q58/vI3KulVzNKJJt2hIrwlUBAAyuBoo8pjmF+UznjveYKiVcnc26lNdTo4RKLGcECgALeHO6d4x+aNYA4VQT74f3hiFeJpNE9UoPG+u+CSrBKSjQULQq9xJ1eYTy2zgL88NKCEYOvGEzOaXfKn41ySNKPlt7AMFnD6KzCvyZBCCPOmiVOZ/PITQLb7srBzwuOyNakL9GQcux0EuE7NXbXbcgItuwADqpG1YCwnVKUFqnwZpcJXdOAAhzy3A5t4OToG7/sj0ydcM9xjJjZoNpKFfEMJuDAA4jdJzCQt/ZRsqKARs4QLfigC0nrdIhLw14XuoujuGXC0QiiJGrnSfwGyhsfsl/TCF6dZsXrckuuzt0JFPFms5MtVL2u7p5PQtfNJDVefmLzYwpDKzmGdwlYeD4WzY9bKOwdOFaRKmazasHExN/SI2OjN98aoU73NyobBjX/CyYZX4Rb2XttvAZjdCvEnvFIOIyK+n1ovbgZ/jnadqBxtcHkixQFSqdHpi+qeg2F7N1LjouGaVVElA+GIaEZzGcj/XcFbjwzZQ/hkyDFQqtEkaP86Eh2qQNx/s4j5tTcWxni4IafwKczqE2Efrlt2KHxOJAk2ogFIfUNtn696JnGlqbhbHpUePtjvTRaytG24XliolWNSnIeiofpp9Q/KV5wuejioOfpmFyBwG8uhmyrThFf7VietCdnKb4LwzbwMVFWnOPrae774N2BSv5DiW2nwmMxvhQUpBwr3ouL0KSAv333p0ASz74JUYHqKx lJ8NJrVm 9bI1huVFuvTrZYcpCI7VE2+YClKKEe6V0oRN0bAMXzrHGOiEs8tRyYgditQ== 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: List-Subscribe: List-Unsubscribe: On Tue, Jun 04, 2024 at 04:57:17PM +0800, Huang, Ying wrote: > Byungchul Park writes: > > > On Tue, Jun 04, 2024 at 03:57:54PM +0800, Huang, Ying wrote: > >> Byungchul Park writes: > >> > >> > Changes from v1: > >> > 1. Don't allow to resume kswapd if the system is under memory > >> > pressure that might affect direct reclaim by any chance, like > >> > if NR_FREE_PAGES is less than (low wmark + min wmark)/2. > >> > > >> > --->8--- > >> > From 6c73fc16b75907f5da9e6b33aff86bf7d7c9dd64 Mon Sep 17 00:00:00 2001 > >> > From: Byungchul Park > >> > Date: Tue, 4 Jun 2024 15:27:56 +0900 > >> > Subject: [PATCH v2] mm: let kswapd work again for node that used to be hopeless but may not now > >> > > >> > A system should run with kswapd running in background when under memory > >> > pressure, such as when the available memory level is below the low water > >> > mark and there are reclaimable folios. > >> > > >> > However, the current code let the system run with kswapd stopped if > >> > kswapd has been stopped due to more than MAX_RECLAIM_RETRIES failures > >> > until direct reclaim will do for that, even if there are reclaimable > >> > folios that can be reclaimed by kswapd. This case was observed in the > >> > following scenario: > >> > > >> > CONFIG_NUMA_BALANCING enabled > >> > sysctl_numa_balancing_mode set to NUMA_BALANCING_MEMORY_TIERING > >> > numa node0 (500GB local DRAM, 128 CPUs) > >> > numa node1 (100GB CXL memory, no CPUs) > >> > swap off > >> > > >> > 1) Run a workload with big anon pages e.g. mmap(200GB). > >> > 2) Continue adding the same workload to the system. > >> > 3) The anon pages are placed in node0 by promotion/demotion. > >> > 4) kswapd0 stops because of the unreclaimable anon pages in node0. > >> > 5) Kill the memory hoggers to restore the system. > >> > > >> > After restoring the system at 5), the system starts to run without > >> > kswapd. Even worse, tiering mechanism is no longer able to work since > >> > the mechanism relies on kswapd for demotion. > >> > >> We have run into the situation that kswapd is kept in failure state for > >> long in a multiple tiers system. I think that your solution is too > > > > My solution just gives a chance for kswapd to work again even if > > kswapd_failures >= MAX_RECLAIM_RETRIES, if there are potential > > reclaimable folios. That's it. > > > >> limited, because OOM killing may not happen, while the access pattern of > > > > I don't get this. OOM will happen as is, through direct reclaim. > > A system that fails to reclaim via kswapd may succeed to reclaim via > direct reclaim, because more CPUs are used to scanning the page tables. Honestly, I don't think so with this description. The fact that the system hit MAX_RECLAIM_RETRIES means the system is currently hopeless unless reclaiming folios in a stronger way by *direct reclaim*. The solution for this situation should not be about letting more CPUs particiated in reclaiming, again, *at least in this situation*. What you described here is true only in a normal state where the more CPUs work on reclaiming, the more reclaimable folios can be reclaimed. kswapd can be a helper *only* when there are kswapd-reclaimable folios. Byungchul > In a system with NUMA balancing based page promotion and page demotion > enabled, page promotion will wake up kswapd, but kswapd may fail in some > situations. But page promotion will no trigger direct reclaim or OOM. > > >> the workloads may change. We have a preliminary and simple solution for > >> this as follows, > >> > >> https://git.kernel.org/pub/scm/linux/kernel/git/vishal/tiering.git/commit/?h=tiering-0.8&id=17a24a354e12d4d4675d78481b358f668d5a6866 > > > > Whether tiering is involved or not, the same problem can arise if > > kswapd gets stopped due to kswapd_failures >= MAX_RECLAIM_RETRIES. > > Your description is about tiering too. Can you describe a situation > without tiering? > > -- > Best Regards, > Huang, Ying > > > Byungchul > > > >> where we will try to wake up kswapd to check every 10 seconds if kswapd > >> is in failure state. This is another possible solution. > >> > >> > However, the node0 has pages newly allocated after 5), that might or > >> > might not be reclaimable. Since those are potentially reclaimable, it's > >> > worth hopefully trying reclaim by allowing kswapd to work again. > >> > > >> > >> [snip] > >> > >> -- > >> Best Regards, > >> Huang, Ying