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[195.135.220.15]) by mx.google.com with ESMTPS id t57si3425853eda.339.2019.05.13.01.09.31 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 13 May 2019 01:09:31 -0700 (PDT) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id C4E52ADAB; Mon, 13 May 2019 08:09:30 +0000 (UTC) Date: Mon, 13 May 2019 10:09:29 +0200 From: Michal Hocko To: Yang Shi Cc: ying.huang@intel.com, hannes@cmpxchg.org, mgorman@techsingularity.net, kirill.shutemov@linux.intel.com, hughd@google.com, shakeelb@google.com, william.kucharski@oracle.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [v2 PATCH] mm: vmscan: correct nr_reclaimed for THP Message-ID: <20190513080929.GC24036@dhcp22.suse.cz> References: <1557505420-21809-1-git-send-email-yang.shi@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1557505420-21809-1-git-send-email-yang.shi@linux.alibaba.com> User-Agent: Mutt/1.10.1 (2018-07-13) 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 Sat 11-05-19 00:23:40, Yang Shi wrote: > Since commit bd4c82c22c36 ("mm, THP, swap: delay splitting THP after > swapped out"), THP can be swapped out in a whole. But, nr_reclaimed > still gets 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. You are technically right here. This has been a known issue for a while. I am wondering whether somebody actually noticed some misbehavior. Swapping out is a rare event and you have to have a considerable number of THPs to notice. > This change may result in more reclaimed pages than scanned pages showed > by /proc/vmstat since scanning one head page would reclaim 512 base pages. This is quite nasty and confusing. I am worried that having those two unsynced begs for subtle issues. Can we account THP as scanning 512 base pages as well? > Cc: "Huang, Ying" > Cc: Johannes Weiner > Cc: Michal Hocko > Cc: Mel Gorman > Cc: "Kirill A . Shutemov" > Cc: Hugh Dickins > Reviewed-by: Shakeel Butt > Signed-off-by: Yang Shi > --- > v2: Added Shakeel's Reviewed-by > Use hpage_nr_pages instead of compound_order per Huang Ying and William Kucharski > > mm/vmscan.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index fd9de50..4226d6b 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -1446,7 +1446,11 @@ 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 += hpage_nr_pages(page); > > /* > * Is there need to periodically free_page_list? It would > -- > 1.8.3.1 > -- Michal Hocko SUSE Labs