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ESMTP id AD166B428; Wed, 23 Oct 2019 16:20:13 +0000 (UTC) Subject: Re: [RFC PATCH 2/2] mm, vmstat: reduce zone->lock holding time by /proc/pagetypeinfo To: Michal Hocko Cc: Andrew Morton , Mel Gorman , Waiman Long , Johannes Weiner , Roman Gushchin , Konstantin Khlebnikov , Jann Horn , Song Liu , Greg Kroah-Hartman , Rafael Aquini , linux-mm@kvack.org, LKML References: <20191023095607.GE3016@techsingularity.net> <20191023102737.32274-1-mhocko@kernel.org> <20191023102737.32274-3-mhocko@kernel.org> <30211965-8ad0-416d-0fe1-113270bd1ea8@suse.cz> <20191023133720.GA17610@dhcp22.suse.cz> <7fb34979-66a4-4a5d-1798-402826e31e72@suse.cz> <20191023143102.GI17610@dhcp22.suse.cz> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; prefer-encrypt=mutual; keydata= mQINBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 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xVKRSg3I2m+DUTVqBy7Lixo73hnW69kSjtqCeamY/NSu6LNP+b0wAOKhwz9hBEwEHLp05+mj 5ZFJyfGsOiNUcMoO/17FO4EBxSDP3FDLllpuzlFD7SXkfJaMWYmXIlO0jLzdfwfcnDzBbPwO hBM8hvtsyq8lq8vJOxv6XD6xcTtj5Az8t2JjdUX6SF9hxJpwhBU0wrCoGDkWp4Bbv6jnF7zP Nzftr4l8RuJoywDIiJpdaNpSlXKpj/K6KrnyAI/joYc7 Message-ID: <8b5a9ee8-4e52-f98c-d833-2e8493baa3a6@suse.cz> Date: Wed, 23 Oct 2019 18:20:08 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.0 MIME-Version: 1.0 In-Reply-To: <20191023143102.GI17610@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/23/19 4:31 PM, Michal Hocko wrote: > On Wed 23-10-19 15:48:36, Vlastimil Babka wrote: >> On 10/23/19 3:37 PM, Michal Hocko wrote: >>> >>> But those wouldn't really help to prevent from the lockup, right? >> >> No, but it would perhaps help ensure that only people who know what they >> are doing (or been told so by a developer e.g. on linux-mm) will try to >> collect the data, and not some automatic monitoring tools taking >> periodic snapshots of stuff in /proc that looks interesting. > > Well, we do trust root doesn't do harm, right? Perhaps too much :) >>> Besides that who would enable that config and how much of a difference >>> would root only vs. debugfs make? >> >> I would hope those tools don't scrap debugfs as much as /proc, but I >> might be wrong of course :) >> >>> Is the incomplete value a real problem? >> >> Hmm perhaps not. If the overflow happens only for one migratetype, one >> can use also /proc/buddyinfo to get to the exact count, as was proposed >> in this thread for Movable migratetype. > > Let's say this won't be the case. What is the worst case that the > imprecision would cause? In other words. Does it really matter whether > we have 100k pages on the free list of the specific migrate type for > order or say 200k? Probably not, it rather matters for which order the count approaches zero.