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[195.135.220.15]) by mx.google.com with ESMTPS id i20si6219051eja.213.2019.02.28.00.06.56 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 28 Feb 2019 00:06:56 -0800 (PST) Received-SPF: pass (google.com: domain of vbabka@suse.cz designates 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=pass (google.com: domain of vbabka@suse.cz designates 195.135.220.15 as permitted sender) smtp.mailfrom=vbabka@suse.cz 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 A152DAD9F; Thu, 28 Feb 2019 08:06:55 +0000 (UTC) Subject: Re: [PATCH] mm,mremap: Bail out earlier in mremap_to under map pressure To: Oscar Salvador , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, hughd@google.com, kirill@shutemov.name, joel@joelfernandes.org, jglisse@redhat.com, yang.shi@linux.alibaba.com, mgorman@techsingularity.net References: <20190226091314.18446-1-osalvador@suse.de> <20190226140428.3e7c8188eda6a54f9da08c43@linux-foundation.org> <20190227213205.5wdjucqdgfqx33tr@d104.suse.de> From: Vlastimil Babka Openpgp: preference=signencrypt Autocrypt: addr=vbabka@suse.cz; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <20190227213205.5wdjucqdgfqx33tr@d104.suse.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US 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 2/27/19 10:32 PM, Oscar Salvador wrote: > On Tue, Feb 26, 2019 at 02:04:28PM -0800, Andrew Morton wrote: >> How is this going to affect existing userspace which is aware of the >> current behaviour? > > Well, current behavior is not really predictable. > Our customer was "surprised" that the call to mremap() failed, but the regions > got unmapped nevertheless. > They found it the hard way when they got a segfault when trying to write to those > regions when cleaning up. > > As I said in the changelog, the possibility for false positives exists, due to > the fact that we might get rid of several vma's when unmapping, but I do not > expect existing userspace applications to start failing. > Should be that the case, we can revert the patch, it is not that it adds a lot > of churn. Hopefully the only program that would start failing would be a LTP test testing the current behavior near the limit (if such test exists). And that can be adjusted. >> And how does it affect your existing cleanup code, come to that? Does >> it work as well or better after this change? > > I guess the customer can trust more reliable that the maps were left untouched. > I still have my reserves though. > > We can get as far as move_vma(), and copy_vma() can fail returning -ENOMEM. > (Or not due to the "too small to fail" ?) >