From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from invmail4.hynix.com (exvmail4.hynix.com [166.125.252.92]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 0E7A565C for ; Wed, 5 Jun 2024 00:21:22 +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=1717546889; cv=none; b=patg1bjJYHwz/PQESfK224eDKOAQ3gt7hvR0mB8XeQs1/reBDMCveRGA7JxNYPZG8nuP/t9Lpb/ZACNxN18UdXSW2qM3Zs290EIW7JyQn0BJRwq96qNBpV0TGzFyFNHlzNpcKNqrzU9LeGOi3ayqtHCLOUOmlRD7xnzNeimNwTA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717546889; c=relaxed/simple; bh=xdfWrF1qujjwhxwbb6igPTngTXPnCU+wUDMmn5J4rlg=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=UdgBhMbaHSjVro9A05kedQt8+VjE37GKBGGjr3xODRmGpUeZyA6YKsl/dT7svRF9T7ap2YJUTZhKEitHi9MIWygXyKGmqnb4MjEqLjNqNLYOFz5yPVWprHgIkaUe3laYiGuwxnKZ3uIScy6WqPo5zRTYTyIbnvhbxezPAk7TLGc= 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-d85ff70000001748-85-665faf7fe9ab Date: Wed, 5 Jun 2024 09:21:14 +0900 From: Byungchul Park To: Johannes Weiner Cc: "Huang, Ying" , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel_team@skhynix.com, 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: <20240605002114.GA23651@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> <20240604091221.GA28034@system.software.com> <20240604102516.GB28034@system.software.com> <20240604122927.GA1992@cmpxchg.org> 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: <20240604122927.GA1992@cmpxchg.org> User-Agent: Mutt/1.9.4 (2018-02-28) X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFrrPLMWRmVeSWpSXmKPExsXC9ZZnoW79+vg0g8dNlhZz1q9hs1i9yddi ZXczm8XlXXPYLO6t+c9q0bZkI5PFyVmTWRzYPQ6/ec/ssWBTqcfiPS+ZPDZ9msTu0fX2CpPH iRm/WTw+b5ILYI/isklJzcksSy3St0vgyjh85BVLwXbtilMbNjA1MPYodjFyckgImEic/feJ BcZ+d/ghE4jNIqAi8fruYTCbTUBd4saNn8wgtoiAhsSlRR1sXYxcHMwCBxkl3hy8y97FyMEh LJAqcXx7AEgNr4CFxOW3T1hBaoQELjBJzPl7kBUiIShxcuYTsGXMAloSN/69ZALpZRaQllj+ jwMkzClgIHFq9y+wvaICyhIHth1nApkjIXCATeLb3XnsEIdKShxccYNlAqPALCRjZyEZOwth 7AJG5lWMQpl5ZbmJmTkmehmVeZkVesn5uZsYgcG+rPZP9A7GTxeCDzEKcDAq8fDu+BWXJsSa WFZcmXuIUYKDWUmE1684Pk2INyWxsiq1KD++qDQntfgQozQHi5I4r9G38hQhgfTEktTs1NSC 1CKYLBMHp1QDY6PNjVDTgu/y6e1XTz5t2LjP/r5fw579R167LJP4LvFfmrt1flOUmZeg7M3S Ag6tk7fZ3DdsWW8WvHDDvDlH17ZyXTmoWxjHXBEfcWxfw8/90lNWz/33KHbninWeT///6Nef e5nv7K/GGM6Ga4zXv3V8SxK9/Wb5H46+4psPW3JUNaw+v+N3WKTEUpyRaKjFXFScCADDet72 cgIAAA== X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFjrGLMWRmVeSWpSXmKPExsXC5WfdrFu/Pj7N4OV2Q4s569ewWaze5Gux sruZzeLw3JOsFpd3zWGzuLfmP6tF25KNTBYnZ01mceDwOPzmPbPHgk2lHov3vGTy2PRpErtH 19srTB4nZvxm8Vj84gOTx+dNcgEcUVw2Kak5mWWpRfp2CVwZh4+8YinYrl1xasMGpgbGHsUu Rk4OCQETiXeHHzKB2CwCKhKv7x4Gs9kE1CVu3PjJDGKLCGhIXFrUwdbFyMXBLHCQUeLNwbvs XYwcHMICqRLHtweA1PAKWEhcfvuEFaRGSOACk8ScvwdZIRKCEidnPmEBsZkFtCRu/HvJBNLL LCAtsfwfB0iYU8BA4tTuX2B7RQWUJQ5sO840gZF3FpLuWUi6ZyF0L2BkXsUokplXlpuYmWOq V5ydUZmXWaGXnJ+7iREYustq/0zcwfjlsvshRgEORiUe3h2/4tKEWBPLiitzDzFKcDArifD6 FcenCfGmJFZWpRblxxeV5qQWH2KU5mBREuf1Ck9NEBJITyxJzU5NLUgtgskycXBKNTC6sbG/ PHtPWjky/ZJIuPn9nW8tzu99p3l0fVX0TxPtLcI/Fuww4zXR3Pvif1DIsT/rl+894bWsSfje tZ911hrfNQonNH/4cay+82FUkcKcqwssGNd8mlduqHfrN/ueBclpz+0nKJwyT9yQtO1n3lKn XRvf3+ePPc2Zkn39xK+Lf79O6/y9jF/ujxJLcUaioRZzUXEiACWHbTNZAgAA X-CFilter-Loop: Reflected On Tue, Jun 04, 2024 at 08:29:27AM -0400, Johannes Weiner wrote: > On Tue, Jun 04, 2024 at 07:25:16PM +0900, Byungchul Park wrote: > > On Tue, Jun 04, 2024 at 06:12:22PM +0900, Byungchul Park wrote: > > > 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. > > > > > > > > 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 > > > > > > I mentioned "tiering" while I described how to reproduce because I ran > > > into the situation while testing with tiering system but I don't think > > > it's the necessary condition. > > > > > > Let me ask you back, why the logic to stop kswapd was considered in the > > > first place? That's because the problem was already observed anyway > > > > To be clear.. > > > > The problem, kswapd_failures >= MAX_RECLAIM_RETRIES, can happen whether > > tiering is involved not not. Once kswapd stops, the system should run > > without kswapd even after recovered e.g. by killing the hoggers. *Even > > worse*, tiering mechanism doesn't work in this situation. > > But like Ying said, in other situations it's direct reclaim that kicks > in and clears the flag. I already described it in the commit message. > The failure-sleep and direct reclaim triggered recovery have been in Sure. It's better than nothing. > place since 2017. Both parties who observed an issue with it recently > did so in tiering scenarios. IMO a tiering-specific solution makes the > most sense. So.. Is the follow situation in a non-tiering system okay? Really? A system runs with kswapd disabled unless hitting min water mark, even if there might be something that kswapd can work on. I don't undertand why it's okay. Could you explain more? Then why do we use kswapd in background? Byungchul