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 2786963D for ; Wed, 5 Jun 2024 01:50:27 +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=1717552234; cv=none; b=hm6Ii4Sro8XYwYNMEkenDksPu6/7xDK3hgxGHJQRWwhGnd+XyY1m1Jb/pnbW0kQ8xlf/NjzfUJIjxmW6MriNazKi8mZY/jHG5o9Mhj8Nwdbl9GF3X/Ncmy+UmLoaL8OXW8nVa+0y2fY5blBCRGtIetcm1r6WNUbgqPe/x83vaSE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717552234; c=relaxed/simple; bh=+/WW9mo1VUWRrsh667APns4YfcJSzJ17CdWhqAAm26w=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=he1Hro2CbAit5HiPnio5rcl0SV83dFFR3rsI8JV0ccVaiyuamSsyMevfa49eyUxV+2ltLZFxupBK6Odeh1jkmNtDLu7g5r4XbMIVjj0SXrMaE7laJ/0MxozQ16lNFhsTlNIWXSmX7CFfkqJXj0Z3PxTbCdPTKhd42al5qBYEP88= 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-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> 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: <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 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