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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id c7-20020a811c07000000b0054f69ac5220sm3489851ywc.133.2023.04.17.18.05.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Apr 2023 18:06:01 -0700 (PDT) Date: Mon, 17 Apr 2023 18:05:51 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: Zi Yan cc: Hugh Dickins , "Matthew Wilcox (Oracle)" , Yang Shi , Yu Zhao , linux-mm@kvack.org, "Kirill A . Shutemov" , Ryan Roberts , =?ISO-8859-15?Q?Michal_Koutn=FD?= , Roman Gushchin , Zach O'Keefe , Andrew Morton , David Hildenbrand , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v3 6/7] mm: truncate: split huge page cache page to a non-zero order if possible. In-Reply-To: <0AC0520E-1BD2-497E-A7ED-05394400BFC9@nvidia.com> Message-ID: <8dbb3c83-48d-93d-3e3-4c833b81904@google.com> References: <20230403201839.4097845-1-zi.yan@sent.com> <20230403201839.4097845-7-zi.yan@sent.com> <9dd96da-efa2-5123-20d4-4992136ef3ad@google.com> <0AC0520E-1BD2-497E-A7ED-05394400BFC9@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 0929CC000E X-Stat-Signature: a9cwntijixaqjgbhnrn4wic34kx3titq X-HE-Tag: 1681779962-402689 X-HE-Meta: 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 bRcFCwUi jkjXQOdmEoNsG8n+E8/aH7Idb9QHOF4edlFbTqvh/Scame3sI0Y5ijbZheGLlc/EpbyzFhfOFgom9MJTGXZfFunIH1YnlYhMNcxpvNM7bJd4Ag/erRacuCh9y53gztzVaOiajYVVY4am2lFMIYU+RZcBl8fB748rhtrO6SE7KJ8Vz25xZQMDnIjdDpd42uKKkop9iUpLSiRrbvtibBhABOuSXhOUBz58PjZ91Jm+X4gPR3ypHtIrOjcEQdRVv2TWpFuEpcDwNgHjgYRZ2P3iWMwZzf6ha10KCe094LGLF5bfS0WNFIQwcfGxRuu9V6WRVPMLiYlPDlqrdfyaYat5WO4bD1iojhbJzk9GOdA0ycdLKsx1XQnC0boJid7dh1e4dZY/v 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 Mon, 17 Apr 2023, Zi Yan wrote: > > What do you think? If you have a better idea, I am all ears. And if you > are willing to help me review the more complicated code changes, I am > more than happy to implement it in the next version. :) Sorry, no, not me. You'll have to persuade someone else that "optimizing" truncation is a worthwhile path to pursue (and to pursue now) - I was just trying to illustrate that the current patchset didn't seem very useful. But don't throw your work away. I expect some of it can become useful later e.g. once most of the main filesystems support large folios, and the complication of CONFIG_READ_ONLY_THP_FOR_FS can be deleted. I doubt my "minimizing the number of folios" approach would be worth the effort; I think more likely that we shall settle on an intermediate folio size (between 4K and THP: maybe 64K, but not necessarily the same on all machines or all workloads) to aim for, and then maybe truncation of THP would split to those units. But it's not a job I shall get into - I'll just continue to report and try to fix what bugs I see. Hugh