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[209.85.220.65]) by mx.google.com with SMTPS id e11sor7091768oiy.62.2019.02.18.05.44.09 for (Google Transport Security); Mon, 18 Feb 2019 05:44:10 -0800 (PST) Received-SPF: pass (google.com: domain of lists@bofh.nu designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@bofh-nu.20150623.gappssmtp.com header.s=20150623 header.b=drdfA6Ux; spf=pass (google.com: domain of lists@bofh.nu designates 209.85.220.65 as permitted sender) smtp.mailfrom=lists@bofh.nu DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bofh-nu.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=wFz5T/gKS4sQKCfoA+LnrdX7HOe7jBqNz1iE1oIU+e8=; b=drdfA6UxeMOkGPRrukDac0Pfot+RfjI7X4llH+DqvnrjuMY14f/nJfGe9lu88QsPA/ ZG+V3FrYSD0bDqmCdl24m/ZWWYDoA8rp728t/jWwPlfuS1GTSCKeidWlo71ssgQE47iL PyKI7cSnwttBv0anKgfK/L5qrEGekLuWaV3xKcgGv89ZcatVbOQzWTF6QNJU/4+vqlxb O/3Tq4j8ZHvn4VTXW7JRzwh54XLEo4u5JwT6MXn4ZfgH3jH8ch+uDCje+Fxe2Q1OR5+d sGz9crjI6+erc0Q9MNo0UseeJgH+u4Y8TnhOL5l7m1g9FRAnZr7PmPvs6//v8lcxwust sTgQ== X-Google-Smtp-Source: AHgI3IZdX+BaKD9r8NSRj2jb9ncPlX8I5T5KiNHlt3XTaZjkEcj2TuEK74CefWHQLOWud5almRRl1Nk45eigelx5Kck= X-Received: by 2002:aca:fd4c:: with SMTP id b73mr14874883oii.33.1550497449575; Mon, 18 Feb 2019 05:44:09 -0800 (PST) MIME-Version: 1.0 References: <997509746.100933786.1549350874925.JavaMail.zimbra@redhat.com> In-Reply-To: <997509746.100933786.1549350874925.JavaMail.zimbra@redhat.com> From: Lars Persson Date: Mon, 18 Feb 2019 14:43:58 +0100 Message-ID: Subject: Re: [PATCH v2] mm: page_mapped: don't assume compound page is huge or THP To: Jan Stancek Cc: linux-mm@kvack.org, lersek@redhat.com, alex williamson , aarcange@redhat.com, rientjes@google.com, kirill@shutemov.name, mgorman@techsingularity.net, mhocko@suse.com, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000015, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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. BR, Lars