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[140.211.169.12]) by mx.google.com with ESMTPS id f3si5122081pgs.557.2019.03.21.16.31.49 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 21 Mar 2019 16:31:49 -0700 (PDT) Received-SPF: pass (google.com: domain of akpm@linux-foundation.org designates 140.211.169.12 as permitted sender) client-ip=140.211.169.12; Authentication-Results: mx.google.com; spf=pass (google.com: domain of akpm@linux-foundation.org designates 140.211.169.12 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org Received: from localhost.localdomain (c-73-223-200-170.hsd1.ca.comcast.net [73.223.200.170]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id EA19EF39; Thu, 21 Mar 2019 23:31:48 +0000 (UTC) Date: Thu, 21 Mar 2019 16:31:47 -0700 From: Andrew Morton To: "Aneesh Kumar K.V" Cc: "Kirill A . Shutemov" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dan Williams , Andrea Arcangeli Subject: Re: [PATCH] mm: page_mkclean vs MADV_DONTNEED race Message-Id: <20190321163147.cc2ff090a7388cdb7030eed0@linux-foundation.org> In-Reply-To: <20190321040610.14226-1-aneesh.kumar@linux.ibm.com> References: <20190321040610.14226-1-aneesh.kumar@linux.ibm.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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 Thu, 21 Mar 2019 09:36:10 +0530 "Aneesh Kumar K.V" wrote: > MADV_DONTNEED is handled with mmap_sem taken in read mode. > We call page_mkclean without holding mmap_sem. > > MADV_DONTNEED implies that pages in the region are unmapped and subsequent > access to the pages in that range is handled as a new page fault. > This implies that if we don't have parallel access to the region when > MADV_DONTNEED is run we expect those range to be unallocated. > > w.r.t page_mkclean we need to make sure that we don't break the MADV_DONTNEED > semantics. MADV_DONTNEED check for pmd_none without holding pmd_lock. > This implies we skip the pmd if we temporarily mark pmd none. Avoid doing > that while marking the page clean. > > Keep the sequence same for dax too even though we don't support MADV_DONTNEED > for dax mapping What were the runtime effects of the bug? Did you consider a -stable backport?