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[195.135.220.15]) by mx.google.com with ESMTPS id x34si38443586edm.138.2019.08.09.05.43.26 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 09 Aug 2019 05:43:26 -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 7472BAF10; Fri, 9 Aug 2019 12:43:25 +0000 (UTC) Date: Fri, 9 Aug 2019 14:43:24 +0200 From: Michal Hocko To: Minchan Kim Cc: Andrew Morton , LKML , linux-mm , Miguel de Dios , Wei Wang , Johannes Weiner , Mel Gorman , Nicholas Piggin Subject: [RFC PATCH] mm: drop mark_page_access from the unmap path Message-ID: <20190809124305.GQ18351@dhcp22.suse.cz> References: <20190729074523.GC9330@dhcp22.suse.cz> <20190729082052.GA258885@google.com> <20190729083515.GD9330@dhcp22.suse.cz> <20190730121110.GA184615@google.com> <20190730123237.GR9330@dhcp22.suse.cz> <20190730123935.GB184615@google.com> <20190730125751.GS9330@dhcp22.suse.cz> <20190731054447.GB155569@google.com> <20190731072101.GX9330@dhcp22.suse.cz> <20190806105509.GA94582@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190806105509.GA94582@google.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 Tue 06-08-19 19:55:09, Minchan Kim wrote: > On Wed, Jul 31, 2019 at 09:21:01AM +0200, Michal Hocko wrote: > > On Wed 31-07-19 14:44:47, Minchan Kim wrote: [...] > > > As Nick mentioned in the description, without mark_page_accessed in > > > zapping part, repeated mmap + touch + munmap never acticated the page > > > while several read(2) calls easily promote it. > > > > And is this really a problem? If we refault the same page then the > > refaults detection should catch it no? In other words is the above still > > a problem these days? > > I admit we have been not fair for them because read(2) syscall pages are > easily promoted regardless of zap timing unlike mmap-based pages. > > However, if we remove the mark_page_accessed in the zap_pte_range, it > would make them more unfair in that read(2)-accessed pages are easily > promoted while mmap-based page should go through refault to be promoted. I have really hard time to follow why an unmap special handling is making the overall state more reasonable. Anyway, let me throw the patch for further discussion. Nick, Mel, Johannes what do you think? >From 3821c2e66347a2141358cabdc6224d9990276fec Mon Sep 17 00:00:00 2001 From: Michal Hocko Date: Fri, 9 Aug 2019 14:29:59 +0200 Subject: [PATCH] mm: drop mark_page_access from the unmap path Minchan has noticed that mark_page_access can take quite some time during unmap: : I had a time to benchmark it via adding some trace_printk hooks between : pte_offset_map_lock and pte_unmap_unlock in zap_pte_range. The testing : device is 2018 premium mobile device. : : I can get 2ms delay rather easily to release 2M(ie, 512 pages) when the : task runs on little core even though it doesn't have any IPI and LRU : lock contention. It's already too heavy. : : If I remove activate_page, 35-40% overhead of zap_pte_range is gone : so most of overhead(about 0.7ms) comes from activate_page via : mark_page_accessed. Thus, if there are LRU contention, that 0.7ms could : accumulate up to several ms. bf3f3bc5e734 ("mm: don't mark_page_accessed in fault path") has replaced SetPageReferenced by mark_page_accessed arguing that the former is not sufficient when mark_page_accessed is removed from the fault path because it doesn't promote page to the active list. It is true that a page that is mapped by a single process might not get promoted even when referenced if the reclaim checks it after the unmap but does that matter that much? Can we cosider the page hot if there are no other users? Moreover we do have workingset detection in place since then and so a next refault would activate the page if it was really hot one. Drop the expensive mark_page_accessed and restore SetPageReferenced to transfer the reference information into the struct page for now to reduce the unmap overhead. Should we find workloads that noticeably depend on this behavior we should find a way to make mark_page_accessed less expensive. Signed-off-by: Michal Hocko --- mm/memory.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/memory.c b/mm/memory.c index e2bb51b6242e..ced521df8ee7 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1053,7 +1053,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb, } if (pte_young(ptent) && likely(!(vma->vm_flags & VM_SEQ_READ))) - mark_page_accessed(page); + SetPageReferenced(page); } rss[mm_counter(page)]--; page_remove_rmap(page, false); -- 2.20.1 -- Michal Hocko SUSE Labs