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[115.124.30.56]) by mx.google.com with ESMTPS id k14si15376564ioc.104.2019.05.23.06.55.53 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 23 May 2019 06:55:55 -0700 (PDT) Received-SPF: pass (google.com: domain of yang.shi@linux.alibaba.com designates 115.124.30.56 as permitted sender) client-ip=115.124.30.56; Authentication-Results: mx.google.com; spf=pass (google.com: domain of yang.shi@linux.alibaba.com designates 115.124.30.56 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=01201311R321e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04446;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=11;SR=0;TI=SMTPD_---0TSTyrdx_1558619738; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0TSTyrdx_1558619738) by smtp.aliyun-inc.com(127.0.0.1); Thu, 23 May 2019 21:55:39 +0800 Subject: Re: [v4 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, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1558578458-83807-1-git-send-email-yang.shi@linux.alibaba.com> <1558578458-83807-2-git-send-email-yang.shi@linux.alibaba.com> <87lfyx9vtr.fsf@yhuang-dev.intel.com> From: Yang Shi Message-ID: <18866477-ec08-3571-c7fe-1c8417da6c3a@linux.alibaba.com> Date: Thu, 23 May 2019 21:55:37 +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: <87lfyx9vtr.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 5/23/19 8:52 PM, 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 >> --- >> 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 | 34 ++++++++++++++++++++++------------ >> 1 file changed, 22 insertions(+), 12 deletions(-) >> >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index b65bc50..1b35a7a 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(); >> >> @@ -1129,7 +1130,9 @@ static unsigned long shrink_page_list(struct list_head *page_list, >> >> VM_BUG_ON_PAGE(PageActive(page), page); >> >> - sc->nr_scanned++; >> + /* Account the number of base pages evne though THP */ > s/evne/even/ > >> + nr_pages = 1 << compound_order(page); >> + sc->nr_scanned += nr_pages; >> >> if (unlikely(!page_evictable(page))) >> goto activate_locked; >> @@ -1250,7 +1253,7 @@ 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 THP is split, you need > > sc->nr_scanned -= nr_pages - 1; > > Otherwise the tail pages will be counted twice. Yes, it looks so. > >> @@ -1315,7 +1318,7 @@ static unsigned long shrink_page_list(struct list_head *page_list, >> if (unlikely(PageTransHuge(page))) >> flags |= TTU_SPLIT_HUGE_PMD; >> if (!try_to_unmap(page, flags)) { >> - stat->nr_unmap_fail++; >> + stat->nr_unmap_fail += nr_pages; >> goto activate_locked; >> } >> } >> @@ -1442,7 +1445,11 @@ static unsigned long shrink_page_list(struct list_head *page_list, >> >> unlock_page(page); >> free_it: >> - nr_reclaimed++; >> + /* >> + * THP may get swapped out in a whole, need account >> + * all base pages. >> + */ >> + nr_reclaimed += (1 << compound_order(page)); > Best Regards, > Huang, Ying