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ESMTP id 59561B820; Wed, 23 Oct 2019 13:25:51 +0000 (UTC) Subject: Re: [PATCH] mm/vmstat: Reduce zone lock hold time when reading /proc/pagetypeinfo To: Mel Gorman , Michal Hocko Cc: Mel Gorman , Waiman Long , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Johannes Weiner , Roman Gushchin , Konstantin Khlebnikov , Jann Horn , Song Liu , Greg Kroah-Hartman , Rafael Aquini , David Rientjes References: <20191022162156.17316-1-longman@redhat.com> <20191022165745.GT9379@dhcp22.suse.cz> <20191023083143.GC3016@techsingularity.net> <20191023090422.GK754@dhcp22.suse.cz> <20191023095607.GE3016@techsingularity.net> 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: <4112a06b-bb3e-7d0f-f5b5-64e5eb5dafb4@suse.cz> Date: Wed, 23 Oct 2019 15:25:50 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.2 MIME-Version: 1.0 In-Reply-To: <20191023095607.GE3016@techsingularity.net> Content-Type: text/plain; charset=iso-8859-15 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 11:56 AM, Mel Gorman wrote: > You also have to iterate over them all later in the same function. The the > free counts are per migrate type then they would have to be iterated over > every time. > > Similarly, there would be multiple places where all the counters would > have to be iterated -- find_suitable_fallback, show_free_areas, > fast_isolate_freepages, fill_contig_page_info, zone_init_free_lists etc. > > It'd be a small cost but given that it's aimed at fixing a problem with > reading pagetypeinfo, is it really worth it? I don't think so. I think the largest issue would be that 1) the migratetype would have to be stored somewhere (ok, perhaps that's not an issue as free pages have plenty of space in struct page), and 2) free page merging code (__free_one_page()) would have to start looking at the migratetype and fix up the counters - merging between migratetypes is not prohibited, for good reasons. IIRC David's patch was missing that part. So I would also prefer to avoid that.