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 X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D23A1C433E0 for ; Tue, 16 Mar 2021 06:53:03 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 4E31C65231 for ; Tue, 16 Mar 2021 06:53:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4E31C65231 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id CCB6A6B006C; Tue, 16 Mar 2021 02:53:02 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C7C446B006E; Tue, 16 Mar 2021 02:53:02 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B421C6B0070; Tue, 16 Mar 2021 02:53:02 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0057.hostedemail.com [216.40.44.57]) by kanga.kvack.org (Postfix) with ESMTP id 953C86B006C for ; Tue, 16 Mar 2021 02:53:02 -0400 (EDT) Received: from smtpin18.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 4B9CA181AF5D7 for ; Tue, 16 Mar 2021 06:53:02 +0000 (UTC) X-FDA: 77924820204.18.B3ACBF6 Received: from mga18.intel.com (mga18.intel.com [134.134.136.126]) by imf03.hostedemail.com (Postfix) with ESMTP id 29935C0007CA for ; Tue, 16 Mar 2021 06:53:00 +0000 (UTC) IronPort-SDR: JlfQ+XCzI5JCbXNuRuU/P97dPp4ox4HfV5EZOYylxGsMlYcokMNNXK6miEWlEovS+cCkY0jO8N dOGrkaoyfHRQ== X-IronPort-AV: E=McAfee;i="6000,8403,9924"; a="176806587" X-IronPort-AV: E=Sophos;i="5.81,251,1610438400"; d="scan'208";a="176806587" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Mar 2021 23:52:58 -0700 IronPort-SDR: LnjIfZaHmv9Bcz9AZRG7h/O8IeMPVbpPXUvyRxZdCw2D343gWtQr++qUoITiT7kMvuFxkONk+j GCBDUdJWej0g== X-IronPort-AV: E=Sophos;i="5.81,251,1610438400"; d="scan'208";a="412106243" Received: from unknown (HELO yhuang6-desk1.ccr.corp.intel.com) ([10.239.13.1]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Mar 2021 23:52:54 -0700 From: "Huang, Ying" To: Yu Zhao Cc: linux-mm@kvack.org, Alex Shi , Andrew Morton , Dave Hansen , Hillf Danton , Johannes Weiner , Joonsoo Kim , Matthew Wilcox , Mel Gorman , Michal Hocko , Roman Gushchin , Vlastimil Babka , Wei Yang , Yang Shi , linux-kernel@vger.kernel.org, page-reclaim@google.com Subject: Re: [PATCH v1 10/14] mm: multigenerational lru: core References: <87im5rsvd8.fsf@yhuang6-desk1.ccr.corp.intel.com> Date: Tue, 16 Mar 2021 14:52:52 +0800 In-Reply-To: (Yu Zhao's message of "Mon, 15 Mar 2021 22:45:18 -0600") Message-ID: <87wnu7y4hn.fsf@yhuang6-desk1.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 X-Stat-Signature: fyrskdzk9cpux189th5y15ujztdnjswe X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 29935C0007CA Received-SPF: none (intel.com>: No applicable sender policy available) receiver=imf03; identity=mailfrom; envelope-from=""; helo=mga18.intel.com; client-ip=134.134.136.126 X-HE-DKIM-Result: none/none X-HE-Tag: 1615877580-14016 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: Yu Zhao writes: > On Tue, Mar 16, 2021 at 10:08:51AM +0800, Huang, Ying wrote: >> Yu Zhao writes: >> [snip] >> >> > +/* Main function used by foreground, background and user-triggered aging. */ >> > +static bool walk_mm_list(struct lruvec *lruvec, unsigned long next_seq, >> > + struct scan_control *sc, int swappiness) >> > +{ >> > + bool last; >> > + struct mm_struct *mm = NULL; >> > + int nid = lruvec_pgdat(lruvec)->node_id; >> > + struct mem_cgroup *memcg = lruvec_memcg(lruvec); >> > + struct lru_gen_mm_list *mm_list = get_mm_list(memcg); >> > + >> > + VM_BUG_ON(next_seq > READ_ONCE(lruvec->evictable.max_seq)); >> > + >> > + /* >> > + * For each walk of the mm list of a memcg, we decrement the priority >> > + * of its lruvec. For each walk of memcgs in kswapd, we increment the >> > + * priorities of all lruvecs. >> > + * >> > + * So if this lruvec has a higher priority (smaller value), it means >> > + * other concurrent reclaimers (global or memcg reclaim) have walked >> > + * its mm list. Skip it for this priority to balance the pressure on >> > + * all memcgs. >> > + */ >> > +#ifdef CONFIG_MEMCG >> > + if (!mem_cgroup_disabled() && !cgroup_reclaim(sc) && >> > + sc->priority > atomic_read(&lruvec->evictable.priority)) >> > + return false; >> > +#endif >> > + >> > + do { >> > + last = get_next_mm(lruvec, next_seq, swappiness, &mm); >> > + if (mm) >> > + walk_mm(lruvec, mm, swappiness); >> > + >> > + cond_resched(); >> > + } while (mm); >> >> It appears that we need to scan the whole address space of multiple >> processes in this loop? >> >> If so, I have some concerns about the duration of the function. Do you >> have some number of the distribution of the duration of the function? >> And may be the number of mm_struct and the number of pages scanned. >> >> In comparison, in the traditional LRU algorithm, for each round, only a >> small subset of the whole physical memory is scanned. > > Reasonable concerns, and insightful too. We are sensitive to direct > reclaim latency, and we tuned another path carefully so that direct > reclaims virtually don't hit this path :) > > Some numbers from the cover letter first: > In addition, direct reclaim latency is reduced by 22% at 99th > percentile and the number of refaults is reduced 7%. These metrics are > important to phones and laptops as they are correlated to user > experience. > > And "another path" is the background aging in kswapd: > age_active_anon() > age_lru_gens() > try_walk_mm_list() > /* try to spread pages out across spread+1 generations */ > if (old_and_young[0] >= old_and_young[1] * spread && > min_nr_gens(max_seq, min_seq, swappiness) > max(spread, MIN_NR_GENS)) > return; > > walk_mm_list(lruvec, max_seq, sc, swappiness); > > By default, spread = 2, which makes kswapd slight more aggressive > than direct reclaim for our use cases. This can be entirely disabled > by setting spread to 0, for worloads that don't care about direct > reclaim latency, or larger values, they are more sensitive than > ours. OK, I see. That can avoid the long latency in direct reclaim path. > It's worth noting that walk_mm_list() is multithreaded -- reclaiming > threads can work on different mm_structs on the same list > concurrently. We do occasionally see this function in direct reclaims, > on over-overcommitted systems, i.e., kswapd CPU usage is 100%. Under > the same condition, we saw the current page reclaim live locked and > triggered hardware watchdog timeouts (our hardware watchdog is set to > 2 hours) many times. Just to confirm, in the current page reclaim, kswapd will keep running until watchdog? This is avoided in your algorithm mainly via multi-threading? Or via direct vs. reversing page table scanning? Best Regards, Huang, Ying