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Shutemov" To: Michal Hocko Cc: Alexander Duyck , Alexander Duyck , virtio-dev@lists.oasis-open.org, kvm list , "Michael S. Tsirkin" , Catalin Marinas , David Hildenbrand , Dave Hansen , LKML , Matthew Wilcox , linux-mm , Andrew Morton , will@kernel.org, linux-arm-kernel@lists.infradead.org, Oscar Salvador , Yang Zhang , Pankaj Gupta , Konrad Rzeszutek Wilk , Nitesh Narayan Lal , Rik van Riel , lcapitulino@redhat.com, "Wang, Wei W" , Andrea Arcangeli , ying.huang@intel.com, Paolo Bonzini , Dan Williams , Fengguang Wu , "Kirill A. Shutemov" , Mel Gorman , Vlastimil Babka Subject: Re: [PATCH v9 0/8] stg mail -e --version=v9 \ Message-ID: <20190912102425.wzhhe6ygfgg64sma@box> References: <20190907172225.10910.34302.stgit@localhost.localdomain> <20190910124209.GY2063@dhcp22.suse.cz> <20190910144713.GF2063@dhcp22.suse.cz> <20190910175213.GD4023@dhcp22.suse.cz> <1d7de9f9f4074f67c567dbb4cc1497503d739e30.camel@linux.intel.com> <20190911113619.GP4023@dhcp22.suse.cz> <20190912091925.GM4023@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190912091925.GM4023@dhcp22.suse.cz> User-Agent: NeoMutt/20180716 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, Sep 12, 2019 at 11:19:25AM +0200, Michal Hocko wrote: > On Wed 11-09-19 08:12:03, Alexander Duyck wrote: > > On Wed, Sep 11, 2019 at 4:36 AM Michal Hocko wrote: > > > > > > On Tue 10-09-19 14:23:40, Alexander Duyck wrote: > > > [...] > > > > We don't put any limitations on the allocator other then that it needs to > > > > clean up the metadata on allocation, and that it cannot allocate a page > > > > that is in the process of being reported since we pulled it from the > > > > free_list. If the page is a "Reported" page then it decrements the > > > > reported_pages count for the free_area and makes sure the page doesn't > > > > exist in the "Boundary" array pointer value, if it does it moves the > > > > "Boundary" since it is pulling the page. > > > > > > This is still a non-trivial limitation on the page allocation from an > > > external code IMHO. I cannot give any explicit reason why an ordering on > > > the free list might matter (well except for page shuffling which uses it > > > to make physical memory pattern allocation more random) but the > > > architecture seems hacky and dubious to be honest. It shoulds like the > > > whole interface has been developed around a very particular and single > > > purpose optimization. > > > > How is this any different then the code that moves a page that will > > likely be merged to the tail though? > > I guess you are referring to the page shuffling. If that is the case > then this is an integral part of the allocator for a reason and it is > very well obvious in the code including the consequences. I do not > really like an idea of hiding similar constrains behind a generic > looking feature which is completely detached from the allocator and so > any future change of the allocator might subtly break it. I don't necessary follow why shuffling is more integral to page allocator than reporting would be. It's next to shutffle.c under mm/ and integrated in a simillar way. -- Kirill A. Shutemov