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[198.145.29.99]) by mx.google.com with ESMTPS id c139si7430407pfb.281.2019.02.06.12.14.32 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 06 Feb 2019 12:14:32 -0800 (PST) Received-SPF: pass (google.com: domain of jikos@kernel.org designates 198.145.29.99 as permitted sender) client-ip=198.145.29.99; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=default header.b=LldSWTZg; spf=pass (google.com: domain of jikos@kernel.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=jikos@kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: from pobox.suse.cz (prg-ext-pat.suse.com [213.151.95.130]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8821420823; Wed, 6 Feb 2019 20:14:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1549484071; bh=D/jyviaLgSda2+tt19m/3P0OWxLRwvwSZ0CI7AZU3po=; h=Date:From:To:cc:Subject:In-Reply-To:References:From; b=LldSWTZgw7Qnu3m7DgpdJe/O3fRySBiF9x5ihc4fFM5ZNkcbnSpaDbuLf2s1gqalI qx8l6W8sFMXpe85Q3jYp97Uyk3pjmIsVbzX3siDZlFWRgLV//nQDRKQ9pH4fuDjDWe rqURUZjmRNNOXwspDe0A98cQHP3nME7OXYXak8Gc= Date: Wed, 6 Feb 2019 21:14:26 +0100 (CET) From: Jiri Kosina To: Vlastimil Babka , Linus Torvalds cc: Michal Hocko , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-api@vger.kernel.org, Peter Zijlstra , Greg KH , Jann Horn , Dominique Martinet , Andy Lutomirski , Dave Chinner , Kevin Easton , Matthew Wilcox , Cyril Hrubis , Tejun Heo , "Kirill A . Shutemov" , Daniel Gruss , Josh Snyder Subject: Re: [PATCH 3/3] mm/mincore: provide mapped status when cached status is not allowed In-Reply-To: Message-ID: References: <20190130124420.1834-1-vbabka@suse.cz> <20190130124420.1834-4-vbabka@suse.cz> <20190131100907.GS18811@dhcp22.suse.cz> <99ee4d3e-aeb2-0104-22be-b028938e7f88@suse.cz> <20190201091152.GG11599@dhcp22.suse.cz> User-Agent: Alpine 2.21 (LSU 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII 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 Fri, 1 Feb 2019, Vlastimil Babka wrote: > > Well, but rss update will not tell you that the page has been faulted in > > which is the most interesting part. > > Sure, but the patch doesn't add back that capability neither. It allows > to recognize page being reclaimed, and I argue you can infer that from > rss change as well. That change is mentioned in the last paragraph in > changelog, and I thought "add a hard to evaluate side channel" in your > reply referred to that. It doesn't add back the "original" side channel > to detect somebody else accessed a page. On Fri, 1 Feb 2019, Vlastimil Babka wrote: > > Is this really worth it? Do we know about any specific usecase that > > would benefit from this change? TBH I would rather wait for the report > > than add a hard to evaluate side channel. > > Well it's not that complicated IMHO. Linus said it's worth trying, so > let's see how he likes the result. The side channel exists anyway as > long as process can e.g. check if its rss shrinked, and I doubt we are > going to remove that possibility. Linus, do you have any opinion here? I have a hunch that mm maintainers are keeping this on a backburner because there might still open question(s) in the air. Thanks, -- Jiri Kosina SUSE Labs