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[142.162.115.133]) by smtp.gmail.com with ESMTPSA id p23sm455107qtu.4.2021.01.26.18.10.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 26 Jan 2021 18:10:23 -0800 (PST) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1l4aHn-007JtW-3N; Tue, 26 Jan 2021 22:10:23 -0400 Date: Tue, 26 Jan 2021 22:10:23 -0400 From: Jason Gunthorpe To: Mike Kravetz Cc: "Matthew Wilcox (Oracle)" , Joao Martins , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , John Hubbard , Dave Hansen Subject: Re: [PATCH 2/2] mm/hugetlb: refactor subpage recording Message-ID: <20210127021023.GC4605@ziepe.ca> References: <20210125205744.10203-1-joao.m.martins@oracle.com> <20210125205744.10203-3-joao.m.martins@oracle.com> <3d34111f-8365-ab95-af11-aaf4825204be@oracle.com> <1ae0313d-de9b-4553-1f68-04c4f5a3f7eb@oracle.com> <4d3914e9-f448-8a86-9fc6-e71cec581115@oracle.com> <20210127000730.GB4605@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Tue, Jan 26, 2021 at 05:58:53PM -0800, Mike Kravetz wrote: > As pointed out by Joao, you can also see the differences in pfn_to_page > for CONFIG_SPARSE_VMEMMAP and CONFIG_SPARSEMEM. The only time we might > have issues is with CONFIG_SPARSEMEM. I would bet CONFIG_SPARSE_VMEMMAP > is far more common. I think it is fine to have a different pfn_to_page, it should just be illegal to combine pages into a compound if their tail pages are not linear in the map. Matt's folio work might present an option to audit the whole mm for this pattern and provide some folio_next_tail_page() accessor that does the fast thing - but I question the value of such a project for a 2008 era PPC platform with 16GB pages (seriously?) that may be using VMEMMAP today anyhow?? Maybe others know of more modern use cases Jason