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[209.85.220.65]) by mx.google.com with SMTPS id i63sor1865138ybg.17.2019.05.09.17.40.09 for (Google Transport Security); Thu, 09 May 2019 17:40:09 -0700 (PDT) Received-SPF: pass (google.com: domain of shakeelb@google.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b=BnWMeilq; spf=pass (google.com: domain of shakeelb@google.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=shakeelb@google.com; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=kJIkcAZ6u5IJ9XmF7NOxVNNYB8HdaXRsalPuY1w3/z8=; b=BnWMeilq5CmV7xEOS7UTY0R8GZBvNiJUb5X8thIrkLC146CGJ28ux8O51ka94luUji ko51fW4KRyCWVOi/von/XCjTv5Bq+D0G0m8PuWDLMU8pmLoHkVAidAi/9MCw72ZNpUBN q7xTRHcayJCQmsiAPDShWGpwdLShGMWkoOMABic60GtN3IaFoPIX9eSVsFIkBfxpV7pe K1YZw/DNtI7wDyhVsKXKTR6evCj+wKBM/ZCKAVbXjVWRlyOHkScfk3FLQ4FnRkjbDi/x TcZbJlD57h5bUMnjLqNuuD1i4+gmaFje2JyxaP3cHRb97P+2aaN1Ctg2LNMnSUH9vTQS 7NZA== X-Google-Smtp-Source: APXvYqw2dVC2ET7GPFNXeSlt/NpFnxG8e1iXqGKojoN4LujAfzUVvhzsWFouCtyUPIv6d5hMLtOYG5Es5WGTXBS03mU= X-Received: by 2002:a25:4147:: with SMTP id o68mr4131573yba.148.1557448809031; Thu, 09 May 2019 17:40:09 -0700 (PDT) MIME-Version: 1.0 References: <1557447392-61607-1-git-send-email-yang.shi@linux.alibaba.com> In-Reply-To: <1557447392-61607-1-git-send-email-yang.shi@linux.alibaba.com> From: Shakeel Butt Date: Thu, 9 May 2019 17:39:57 -0700 Message-ID: Subject: Re: [PATCH] mm: vmscan: correct nr_reclaimed for THP To: Yang Shi Cc: Huang Ying , Johannes Weiner , Michal Hocko , Mel Gorman , "Kirill A. Shutemov" , Hugh Dickins , Andrew Morton , Linux MM , LKML Content-Type: text/plain; charset="UTF-8" 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: From: Yang Shi Date: Thu, May 9, 2019 at 5:16 PM To: , , , , , , Cc: , , > 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. > > 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. > > Cc: "Huang, Ying" > Cc: Johannes Weiner > Cc: Michal Hocko > Cc: Mel Gorman > Cc: "Kirill A . Shutemov" > Cc: Hugh Dickins > Signed-off-by: Yang Shi Nice find. Reviewed-by: Shakeel Butt > --- > I'm not quite sure if it was the intended behavior or just omission. I tried > to dig into the review history, but didn't find any clue. I may miss some > discussion. > > mm/vmscan.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index fd9de50..7e026ec 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 += (1 << compound_order(page)); > > /* > * Is there need to periodically free_page_list? It would > -- > 1.8.3.1 >