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Shutemov" To: Vlastimil Babka Cc: linux-mm@kvack.org, Andrew Morton , linux-kernel@vger.kernel.org, "Kirill A. Shutemov" , Michal Hocko , Mel Gorman , Matthew Wilcox Subject: Re: [PATCH 1/3] mm, page_owner: record page owner for each subpage Message-ID: <20190816140430.aoya6k7qxxrls72h@box> References: <20190816101401.32382-1-vbabka@suse.cz> <20190816101401.32382-2-vbabka@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190816101401.32382-2-vbabka@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 Fri, Aug 16, 2019 at 12:13:59PM +0200, Vlastimil Babka wrote: > Currently, page owner info is only recorded for the first page of a high-order > allocation, and copied to tail pages in the event of a split page. With the > plan to keep previous owner info after freeing the page, it would be benefical > to record page owner for each subpage upon allocation. This increases the > overhead for high orders, but that should be acceptable for a debugging option. > > The order stored for each subpage is the order of the whole allocation. This > makes it possible to calculate the "head" pfn and to recognize "tail" pages > (quoted because not all high-order allocations are compound pages with true > head and tail pages). When reading the page_owner debugfs file, keep skipping > the "tail" pages so that stats gathered by existing scripts don't get inflated. > > Signed-off-by: Vlastimil Babka Hm. That's all reasonable, but I have a question: do you see how page owner thing works for THP now? I don't see anything in split_huge_page() path (do not confuse it with split_page() path) that would copy the information to tail pages. Do you? -- Kirill A. Shutemov