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[142.162.115.133]) by smtp.gmail.com with ESMTPSA id n35sm13481022qte.19.2021.02.23.10.54.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 23 Feb 2021 10:54:36 -0800 (PST) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1lEcpP-00FTUQ-TH; Tue, 23 Feb 2021 14:54:35 -0400 Date: Tue, 23 Feb 2021 14:54:35 -0400 From: Jason Gunthorpe To: Dan Williams Cc: Joao Martins , Linux MM , Ira Weiny , linux-nvdimm , Matthew Wilcox , Jane Chu , Muchun Song , Mike Kravetz , Andrew Morton Subject: Re: [PATCH RFC 0/9] mm, sparse-vmemmap: Introduce compound pagemaps Message-ID: <20210223185435.GO2643399@ziepe.ca> References: <20201208172901.17384-1-joao.m.martins@oracle.com> <6a18179e-65f7-367d-89a9-d5162f10fef0@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: EB0B3200039D X-Stat-Signature: 8b7bedyizcf39ri8b8t384cs51h6uet4 Received-SPF: none (ziepe.ca>: No applicable sender policy available) receiver=imf11; identity=mailfrom; envelope-from=""; helo=mail-qk1-f177.google.com; client-ip=209.85.222.177 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1614106468-624155 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, Feb 23, 2021 at 08:44:52AM -0800, Dan Williams wrote: > > The downside would be one extra lookup in dev_pagemap tree > > for other pgmap->types (P2P, FSDAX, PRIVATE). But just one > > per gup-fast() call. > > I'd guess a dev_pagemap lookup is faster than a get_user_pages slow > path. It should be measurable that this change is at least as fast or > faster than falling back to the slow path, but it would be good to > measure. What is the dev_pagemap thing doing in gup fast anyhow? I've been wondering for a while.. Jason