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 0A0F5C4332F for ; Wed, 30 Nov 2022 05:33:04 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 9FE7F6B0075; Wed, 30 Nov 2022 00:33:03 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 9AE886B0078; Wed, 30 Nov 2022 00:33:03 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 89E796B007B; Wed, 30 Nov 2022 00:33:03 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 7D68B6B0075 for ; Wed, 30 Nov 2022 00:33:03 -0500 (EST) Received: from smtpin27.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 4B04D1A020A for ; 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29 Nov 2022 21:32:59 -0800 X-IronPort-AV: E=McAfee;i="6500,9779,10546"; a="732846296" X-IronPort-AV: E=Sophos;i="5.96,205,1665471600"; d="scan'208";a="732846296" Received: from yhuang6-desk2.sh.intel.com (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.238.208.55]) by fmsmga003-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Nov 2022 21:32:56 -0800 From: "Huang, Ying" To: Yang Shi Cc: Johannes Weiner , Mina Almasry , Yang Shi , Yosry Ahmed , Tim Chen , weixugc@google.com, shakeelb@google.com, gthelen@google.com, fvdl@google.com, Michal Hocko , Roman Gushchin , Muchun Song , Andrew Morton , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC PATCH V1] mm: Disable demotion from proactive reclaim References: <20221122203850.2765015-1-almasrymina@google.com> <874juonbmv.fsf@yhuang6-desk2.ccr.corp.intel.com> <87a64ad1iz.fsf@yhuang6-desk2.ccr.corp.intel.com> Date: Wed, 30 Nov 2022 13:31:51 +0800 In-Reply-To: (Yang Shi's message of "Tue, 29 Nov 2022 09:27:33 -0800") Message-ID: <87ilixatyw.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii ARC-Authentication-Results: i=1; imf19.hostedemail.com; dkim=none ("invalid DKIM record") header.d=intel.com header.s=Intel header.b=oIbVB3XN; spf=pass (imf19.hostedemail.com: domain of ying.huang@intel.com designates 134.134.136.24 as permitted sender) smtp.mailfrom=ying.huang@intel.com; dmarc=pass (policy=none) header.from=intel.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1669786383; a=rsa-sha256; cv=none; b=J405oeq9r56Dl9boQo82RdFJopoNMgg8AuXzthRcyloWayCGXkm6Ps5LZ/8Zc3U2IB1BRA BLQkkb6TKPN7eyPYsUeHUDDv1cULOYDh0f/qhSjlDhCdoFru+cSycTEM0PSMMWbxhrEahm CzkZ9Kh92aerZ1NCxzQJoUM0NIixmhY= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1669786383; 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:dkim-signature; bh=NtfHH6Wj5goqz48HLGTwP7gRGZxBLlD0nx4w16hZHFA=; b=WKXOU9rkqyzHQzCAiUhLyoAUytdqRmXATZhawlpMMgbiDp5C5kOB5nbgPyDJ3FQmE+DtfG PSoRgBR4PetOV+nOuyyvNNbvsrVA3RZTPqo5yOSo5Rb1Pt2W7NkuQrljErZTbb6OZPXTBb cD83WJC35CRrcxCNgJ5ZckSQL+kU/wk= X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 8B4741A000E Authentication-Results: imf19.hostedemail.com; dkim=none ("invalid DKIM record") header.d=intel.com header.s=Intel header.b=oIbVB3XN; spf=pass (imf19.hostedemail.com: domain of ying.huang@intel.com designates 134.134.136.24 as permitted sender) smtp.mailfrom=ying.huang@intel.com; dmarc=pass (policy=none) header.from=intel.com X-Stat-Signature: 8twfm7sxrb6tytzn1o14ihqjaon1dq4i X-HE-Tag: 1669786381-132947 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: Yang Shi writes: > On Mon, Nov 28, 2022 at 4:54 PM Huang, Ying wrote: >> >> Yang Shi writes: >> >> > On Wed, Nov 23, 2022 at 9:52 PM Huang, Ying wrote: >> >> >> >> Hi, Johannes, >> >> >> >> Johannes Weiner writes: >> >> [...] >> >> > >> >> > The fallback to reclaim actually strikes me as wrong. >> >> > >> >> > Think of reclaim as 'demoting' the pages to the storage tier. If we >> >> > have a RAM -> CXL -> storage hierarchy, we should demote from RAM to >> >> > CXL and from CXL to storage. If we reclaim a page from RAM, it means >> >> > we 'demote' it directly from RAM to storage, bypassing potentially a >> >> > huge amount of pages colder than it in CXL. That doesn't seem right. >> >> > >> >> > If demotion fails, IMO it shouldn't satisfy the reclaim request by >> >> > breaking the layering. Rather it should deflect that pressure to the >> >> > lower layers to make room. This makes sure we maintain an aging >> >> > pipeline that honors the memory tier hierarchy. >> >> >> >> Yes. I think that we should avoid to fall back to reclaim as much as >> >> possible too. Now, when we allocate memory for demotion >> >> (alloc_demote_page()), __GFP_KSWAPD_RECLAIM is used. So, we will trigger >> >> kswapd reclaim on lower tier node to free some memory to avoid fall back >> >> to reclaim on current (higher tier) node. This may be not good enough, >> >> for example, the following patch from Hasan may help via waking up >> >> kswapd earlier. >> > >> > For the ideal case, I do agree with Johannes to demote the page tier >> > by tier rather than reclaiming them from the higher tiers. But I also >> > agree with your premature OOM concern. >> > >> >> >> >> https://lore.kernel.org/linux-mm/b45b9bf7cd3e21bca61d82dcd1eb692cd32c122c.1637778851.git.hasanalmaruf@fb.com/ >> >> >> >> Do you know what is the next step plan for this patch? >> >> >> >> Should we do even more? >> > >> > In my initial implementation I implemented a simple throttle logic >> > when the demotion is not going to succeed if the demotion target has >> > not enough free memory (just check the watermark) to make migration >> > succeed without doing any reclamation. Shall we resurrect that? >> >> Can you share the link to your throttle patch? Or paste it here? > > I just found this on the mailing list. > https://lore.kernel.org/linux-mm/1560468577-101178-8-git-send-email-yang.shi@linux.alibaba.com/ Per my understanding, this patch will avoid demoting if there's no free space on demotion target? If so, I think that we should trigger kswapd reclaiming on demotion target before that. And we can simply avoid to fall back to reclaim firstly, then avoid to scan as an improvement as that in your patch above. Best Regards, Huang, Ying > But it didn't have the throttling logic, I may not submit that version > to the mailing list since we decided to drop this and merge mine and > Dave's. > > Anyway it is not hard to add the throttling logic, we already have a > few throttling cases in vmscan, for example, "mm/vmscan: throttle > reclaim until some writeback completes if congested". >> >> > Waking kswapd sooner is fine to me, but it may be not enough, for >> > example, the kswapd may not keep up so remature OOM may happen on >> > higher tiers or reclaim may still happen. I think throttling the >> > reclaimer/demoter until kswapd makes progress could avoid both. And >> > since the lower tiers memory typically is quite larger than the higher >> > tiers, so the throttle should happen very rarely IMHO. >> > >> >> >> >> From another point of view, I still think that we can use falling back >> >> to reclaim as the last resort to avoid OOM in some special situations, >> >> for example, most pages in the lowest tier node are mlock() or too hot >> >> to be reclaimed. >> >> >> >> > So I'm hesitant to design cgroup controls around the current behavior. >> >> Best Regards, >> Huang, Ying