From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.16]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6C940F503 for ; Wed, 5 Jun 2024 02:04:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.16 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717553043; cv=none; b=ZTttftI59N8VVRXJgpP7hwUbE23Yow/crEwDDrihCD2zX8qhvH+HTXyasMbU1LEIXxsvTbXOwoMdzc8C7ICrkqZdNbzOEBYvQyphIslpJO81DU2K3lGXfvNFfevUIXMvonIG5JHdM6jdE+r3L3BFwJFzeAj/b2mrK41+ihywGGY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717553043; c=relaxed/simple; bh=6mehi3CoPBEEy+f+M0kPGZBBjoi2oPFm16L/sOvB6ZI=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=sAzflmoZCMOFen4CJEyeNhHiQ5BDlg1U9j1Di2dpFbv9O+xiElIdr8/+PhoqeWLww3Bkwsan2hR2yIgkFo41obtw4FRhhf2fcBF3/v3TtJ0yqfNnBp5T6+2Kzyx8L+/mFqiayrk1b4dX0SmnXhw70yBPK6pa9uKLnffFS1VzpKA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=GgGhPdTg; arc=none smtp.client-ip=198.175.65.16 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="GgGhPdTg" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1717553041; x=1749089041; h=from:to:cc:subject:in-reply-to:references:date: message-id:mime-version; bh=6mehi3CoPBEEy+f+M0kPGZBBjoi2oPFm16L/sOvB6ZI=; b=GgGhPdTgoBW6KbCknGXAhVLvFM6gE1vqSaj+199Su5vYryvOcua7uMEU k6T3V8bdtc9q5fFxXnD52znhU/GtgHNmWHGPuPhRz5bOgg+pwzhETSu6l iwS1YmPDkp+AS4H2UHd7ZBVXf1RPXAP1/zg3ILUYuBoYjlhFegU/jsP4e MKLzqFgNIZpDyAJekeEVHN4BRDxSj8AoofZkC7Ir/39dk33AoWdP4K4Io KpZirPc4xQJE2wa7S338EfexQWh4pdolxPeiXOaJQwngIIH9KMJSDqMT6 bhO1Xe/IU2GTsZuXIYr9IpJ2mxC7H7MgViOGQ40TsCes9TGAX9i+WlJ/C Q==; X-CSE-ConnectionGUID: TrhITBZuTAaVqHAk3XuKlw== X-CSE-MsgGUID: /Kwr8X9BRoK+YVdY68qayQ== X-IronPort-AV: E=McAfee;i="6600,9927,11093"; a="14269847" X-IronPort-AV: E=Sophos;i="6.08,215,1712646000"; d="scan'208";a="14269847" Received: from fmviesa006.fm.intel.com ([10.60.135.146]) by orvoesa108.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Jun 2024 19:04:01 -0700 X-CSE-ConnectionGUID: KXtnQgulR5WKLLd9IyILJw== X-CSE-MsgGUID: 2TVHDZuTTQ2VE9BfPFjcLQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.08,215,1712646000"; d="scan'208";a="37440309" Received: from unknown (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.238.208.55]) by fmviesa006-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Jun 2024 19:03:59 -0700 From: "Huang, Ying" To: Byungchul Park Cc: , , , , , , Subject: Re: [PATCH v2] mm: let kswapd work again for node that used to be hopeless but may not now In-Reply-To: <20240605015021.GB75311@system.software.com> (Byungchul Park's message of "Wed, 5 Jun 2024 10:50:21 +0900") 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> Date: Wed, 05 Jun 2024 10:02:07 +0800 Message-ID: <87tti8b10g.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) 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=ascii 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. -- 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