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[47.88.44.37]) by mx.google.com with ESMTPS id a5si3294418pgg.543.2019.05.26.19.48.08 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 26 May 2019 19:48:09 -0700 (PDT) Received-SPF: pass (google.com: domain of yang.shi@linux.alibaba.com designates 47.88.44.37 as permitted sender) client-ip=47.88.44.37; Authentication-Results: mx.google.com; spf=pass (google.com: domain of yang.shi@linux.alibaba.com designates 47.88.44.37 as permitted sender) smtp.mailfrom=yang.shi@linux.alibaba.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=alibaba.com X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R131e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04395;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=12;SR=0;TI=SMTPD_---0TSlJH2R_1558925274; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0TSlJH2R_1558925274) by smtp.aliyun-inc.com(127.0.0.1); Mon, 27 May 2019 10:47:55 +0800 Subject: Re: [RESEND v5 PATCH 2/2] mm: vmscan: correct some vmscan counters for THP swapout To: "Huang, Ying" Cc: hannes@cmpxchg.org, mhocko@suse.com, mgorman@techsingularity.net, kirill.shutemov@linux.intel.com, josef@toxicpanda.com, hughd@google.com, shakeelb@google.com, hdanton@sina.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1558922275-31782-1-git-send-email-yang.shi@linux.alibaba.com> <1558922275-31782-2-git-send-email-yang.shi@linux.alibaba.com> <87muj88x3p.fsf@yhuang-dev.intel.com> From: Yang Shi Message-ID: Date: Mon, 27 May 2019 10:47:51 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <87muj88x3p.fsf@yhuang-dev.intel.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US 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: On 5/27/19 10:11 AM, Huang, Ying wrote: > Yang Shi writes: > >> Since commit bd4c82c22c36 ("mm, THP, swap: delay splitting THP after >> swapped out"), THP can be swapped out in a whole. But, nr_reclaimed >> and some other vm counters still get inc'ed by one even though a whole >> THP (512 pages) gets swapped out. >> >> This doesn't make too much sense to memory reclaim. For example, direct >> reclaim may just need reclaim SWAP_CLUSTER_MAX pages, reclaiming one THP >> could fulfill it. But, if nr_reclaimed is not increased correctly, >> direct reclaim may just waste time to reclaim more pages, >> SWAP_CLUSTER_MAX * 512 pages in worst case. >> >> And, it may cause pgsteal_{kswapd|direct} is greater than >> pgscan_{kswapd|direct}, like the below: >> >> pgsteal_kswapd 122933 >> pgsteal_direct 26600225 >> pgscan_kswapd 174153 >> pgscan_direct 14678312 >> >> nr_reclaimed and nr_scanned must be fixed in parallel otherwise it would >> break some page reclaim logic, e.g. >> >> vmpressure: this looks at the scanned/reclaimed ratio so it won't >> change semantics as long as scanned & reclaimed are fixed in parallel. >> >> compaction/reclaim: compaction wants a certain number of physical pages >> freed up before going back to compacting. >> >> kswapd priority raising: kswapd raises priority if we scan fewer pages >> than the reclaim target (which itself is obviously expressed in order-0 >> pages). As a result, kswapd can falsely raise its aggressiveness even >> when it's making great progress. >> >> Other than nr_scanned and nr_reclaimed, some other counters, e.g. >> pgactivate, nr_skipped, nr_ref_keep and nr_unmap_fail need to be fixed >> too since they are user visible via cgroup, /proc/vmstat or trace >> points, otherwise they would be underreported. >> >> When isolating pages from LRUs, nr_taken has been accounted in base >> page, but nr_scanned and nr_skipped are still accounted in THP. It >> doesn't make too much sense too since this may cause trace point >> underreport the numbers as well. >> >> So accounting those counters in base page instead of accounting THP as >> one page. >> >> nr_dirty, nr_unqueued_dirty, nr_congested and nr_writeback are used by >> file cache, so they are not impacted by THP swap. >> >> This change may result in lower steal/scan ratio in some cases since >> THP may get split during page reclaim, then a part of tail pages get >> reclaimed instead of the whole 512 pages, but nr_scanned is accounted >> by 512, particularly for direct reclaim. But, this should be not a >> significant issue. >> >> Cc: "Huang, Ying" >> Cc: Johannes Weiner >> Cc: Michal Hocko >> Cc: Mel Gorman >> Cc: "Kirill A . Shutemov" >> Cc: Hugh Dickins >> Cc: Shakeel Butt >> Signed-off-by: Yang Shi >> --- >> v5: Fixed sc->nr_scanned double accounting per Huang Ying >> Added some comments to address the concern about premature OOM per Hillf Danton >> v4: Fixed the comments from Johannes and Huang Ying >> v3: Removed Shakeel's Reviewed-by since the patch has been changed significantly >> Switched back to use compound_order per Matthew >> Fixed more counters per Johannes >> v2: Added Shakeel's Reviewed-by >> Use hpage_nr_pages instead of compound_order per Huang Ying and William Kucharski >> >> mm/vmscan.c | 42 +++++++++++++++++++++++++++++++----------- >> 1 file changed, 31 insertions(+), 11 deletions(-) >> >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index b65bc50..f4f4d57 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -1118,6 +1118,7 @@ static unsigned long shrink_page_list(struct list_head *page_list, >> int may_enter_fs; >> enum page_references references = PAGEREF_RECLAIM_CLEAN; >> bool dirty, writeback; >> + unsigned int nr_pages; >> >> cond_resched(); >> >> @@ -1129,6 +1130,13 @@ static unsigned long shrink_page_list(struct list_head *page_list, >> >> VM_BUG_ON_PAGE(PageActive(page), page); >> >> + nr_pages = 1 << compound_order(page); >> + >> + /* >> + * Accounted one page for THP for now. If THP gets swapped >> + * out in a whole, will account all tail pages later to >> + * avoid accounting tail pages twice. >> + */ >> sc->nr_scanned++; >> >> if (unlikely(!page_evictable(page))) >> @@ -1250,7 +1258,7 @@ static unsigned long shrink_page_list(struct list_head *page_list, >> case PAGEREF_ACTIVATE: >> goto activate_locked; >> case PAGEREF_KEEP: >> - stat->nr_ref_keep++; >> + stat->nr_ref_keep += nr_pages; >> goto keep_locked; >> case PAGEREF_RECLAIM: >> case PAGEREF_RECLAIM_CLEAN: > If the "Accessed bit" of a THP is set in the page table that maps it, it > will go PAGEREF_ACTIVATE path here. And the sc->nr_scanned should > increase 512 instead of 1. Otherwise sc->nr_activate may be larger than > sc->nr_scanned. Yes, it looks so. It seems the easiest way is to add "nr_pages - 1" in activate_locked label if the page is still a THP. If we add all tail pages at the very beginning, then we have to minus tail pages when THP gets split, there are a few places do this. > > Best Regards, > Huang, Ying