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[195.135.220.15]) by mx.google.com with ESMTPS id w1-v6si68630ejf.184.2019.02.18.05.50.03 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 18 Feb 2019 05:50:03 -0800 (PST) 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 63490B015; Mon, 18 Feb 2019 13:50:03 +0000 (UTC) Date: Mon, 18 Feb 2019 14:50:02 +0100 From: Michal Hocko To: Lars Persson Cc: Jan Stancek , linux-mm@kvack.org, lersek@redhat.com, alex williamson , aarcange@redhat.com, rientjes@google.com, kirill@shutemov.name, mgorman@techsingularity.net, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] mm: page_mapped: don't assume compound page is huge or THP Message-ID: <20190218135002.GR4525@dhcp22.suse.cz> References: <997509746.100933786.1549350874925.JavaMail.zimbra@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000052, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon 18-02-19 14:43:58, Lars Persson wrote: > On Tue, Feb 5, 2019 at 8:14 AM Jan Stancek wrote: > > Hi, > > > > are you using THP (CONFIG_TRANSPARENT_HUGEPAGE)? > > > > The changed line should affect only THP and normal compound pages, > > so a test with THP disabled might be interesting. > > > > > > > > The breakage consists of random processes dying with SIGILL or SIGSEGV > > > when we stress test the system with high memory pressure and explicit > > > memory compaction requested through /proc/sys/vm/compact_memory. > > > Reverting this patch fixes the crashes. > > > > > > We can put some effort on debugging if there are no obvious > > > explanations for this. Keep in mind that this is 32-bit system with > > > HIGHMEM. > > > > Nothing obvious that I can see. I've been trying to reproduce on > > 32-bit x86 Fedora with no luck so far. > > > > Hi > > Thanks for looking in to it. After some deep dive in MM code, I think > it is safe to say this patch was innocent. > > All traces studied so far points to a missing cache coherency call in > mm/migrate.c:migrate_page that is needed only for those evil MIPSes > that lack I/D cache coherency. I will send a write-up to linux-mips > about this. Basically for a non-mapped page it does only a copy of > page data and metadata but no flush_dcache_page() call will be done. > This races with subsequent use of the page. Please make sure to cc linux-mm for the patch -- Michal Hocko SUSE Labs