From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from invmail4.hynix.com (exvmail4.skhynix.com [166.125.252.92]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 043941EB36 for ; Wed, 5 Jun 2024 02:19:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=166.125.252.92 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717553957; cv=none; b=ug2te8t3OMb+LFahsQk5o4fRFznPzbIaPRY/rdO2fBuhTY/Be4xLRMQLQIE8r5NKTd+BngIcFKbke0SI3CpB8l8LUvSt8J8rMbUGE5M8autAJd8mXnZlWhHXAoR13e0V0xnCY8jiJW6kT7pPi3RMrEFgGQ4qr9JeVi3P4u1Hh9k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717553957; c=relaxed/simple; bh=Zxkhm0YeSTgwvm9hgTADfpfC5tsKNvUgfM1BTuRDc9M=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=KWlKRBNKM+5Bu6ZJpAXmTACmGjqKpkMaiHnl1GhZtH8FOQK6nA7LKfIbN+pkM6H9Zq37wfRGw+ReNm8AmUrCrZFkc6+B2rKYSTF1HZVTBI8nv43u+0RuGIUlX7J4VNceTaZggxB1QDOF2WDUA/gVy5YLxuMzxyB+wUf+4dbNGhI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=sk.com; spf=pass smtp.mailfrom=sk.com; arc=none smtp.client-ip=166.125.252.92 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=sk.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=sk.com X-AuditID: a67dfc5b-d6dff70000001748-b9-665fcb1bc2af Date: Wed, 5 Jun 2024 11:19:02 +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: <20240605021902.GC75311@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> <20240605015021.GB75311@system.software.com> <87tti8b10g.fsf@yhuang6-desk2.ccr.corp.intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87tti8b10g.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Mutt/1.9.4 (2018-02-28) X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFrrHLMWRmVeSWpSXmKPExsXC9ZZnka7M6fg0g0+7WC3mrF/DZrF6k6/F yu5mNovLu+awWdxb85/Vom3JRiaLk7Mmsziwexx+857ZY8GmUo/Fe14yeWz6NIndo+vtFSaP EzN+s3h83iQXwB7FZZOSmpNZllqkb5fAlbGiaQtLQYd2xb6Pp1gaGDcpdjFycEgImEhcns3d xcgJZl66u5sdxGYRUJGY+/I8C4jNJqAucePGT2YQW0RAQ+LTwuVANVwczAJrGSWOXG1hBZkj LJAqcXx7AEgNr4CFxOlbkxlBaoQE1jNJ/Oh5yQ6REJQ4OfMJ2FBmAS2JG/9eMoH0MgtISyz/ xwES5hSwk3g96RcTiC0qoCxxYNtxJpA5EgIH2CSuXLzAAnGopMTBFTdYJjAKzEIydhaSsbMQ xi5gZF7FKJSZV5abmJljopdRmZdZoZecn7uJERjqy2r/RO9g/HQh+BCjAAejEg/vjl9xaUKs iWXFlbmHGCU4mJVEeP2K49OEeFMSK6tSi/Lji0pzUosPMUpzsCiJ8xp9K08REkhPLEnNTk0t SC2CyTJxcEo1MLZ8W/RmRsXcRV/+eX9Y/P6rYFvfP4V3p0TuWcVc11Pb96jqm8UFt0LvY4Gp YZflbx86J6/3/scv5WUPGe7d/JidcXHN68e1nQKze88pV7xwZVeT57T0rdinFMTwvLlMqE1D a+3aB5duXFwjb/9cMuNmr6nNerMfvdt0jn5cuOcX5wzf+rhpOU+UWIozEg21mIuKEwFUkbkV cQIAAA== X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFjrGLMWRmVeSWpSXmKPExsXC5WfdrCt9Oj7N4NltU4s569ewWaze5Gux sruZzeLw3JOsFpd3zWGzuLfmP6tF25KNTBYnZ01mceDwOPzmPbPHgk2lHov3vGTy2PRpErtH 19srTB4nZvxm8Vj84gOTx+dNcgEcUVw2Kak5mWWpRfp2CVwZK5q2sBR0aFfs+3iKpYFxk2IX IyeHhICJxKW7u9lBbBYBFYm5L8+zgNhsAuoSN278ZAaxRQQ0JD4tXA5Uw8XBLLCWUeLI1RbW LkYODmGBVInj2wNAangFLCRO35rMCFIjJLCeSeJHz0t2iISgxMmZT8CGMgtoSdz495IJpJdZ QFpi+T8OkDCngJ3E60m/mEBsUQFliQPbjjNNYOSdhaR7FpLuWQjdCxiZVzGKZOaV5SZm5pjq FWdnVOZlVugl5+duYgSG7rLaPxN3MH657H6IUYCDUYmHd8evuDQh1sSy4srcQ4wSHMxKIrx+ xfFpQrwpiZVVqUX58UWlOanFhxilOViUxHm9wlMThATSE0tSs1NTC1KLYLJMHJxSDYz7ll+4 Z8p9K/L73U+pjK2aNadbNq3y8o/YO4Vrth3j2jIm9vqXIslZLrZlXsXm1xrjd8p8ervk7LxF PVPPstpIL0s8+G6d500WvgPWIRFVvWdX57V7nJ9k3fuObaMvo2HvEc1JCWp2pyoen9d56bZE bjvLsWcqjX5feTwWbjP7qLO2YlPmbDslluKMREMt5qLiRADujAtHWQIAAA== X-CFilter-Loop: Reflected On Wed, Jun 05, 2024 at 10:02:07AM +0800, Huang, Ying wrote: > Byungchul Park writes: > > > 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. > > Sometimes, we cannot reclaim just because we doesn't scan fast enough so > the Accessed-bit is set again during scanning. With more CPUs, we can > scan faster, so make some progress. But, yes, this only cover one > situation, there are other situations too. What I mean is *the issue we try to solve* is not the situation that can be solved by letting more CPUs participate in reclaiming. Byungchul > -- > Best Regards, > Huang, Ying > > > 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