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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id s2sm7557978qti.54.2021.03.13.19.09.11 (version=TLS1 cipher=ECDHE-ECDSA-AES128-SHA bits=128/128); Sat, 13 Mar 2021 19:09:12 -0800 (PST) Date: Sat, 13 Mar 2021 19:09:01 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Andrew Morton cc: "Matthew Wilcox (Oracle)" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v4 00/25] Page folios In-Reply-To: <20210313123658.ad2dcf79a113a8619c19c33b@linux-foundation.org> Message-ID: References: <20210305041901.2396498-1-willy@infradead.org> <20210313123658.ad2dcf79a113a8619c19c33b@linux-foundation.org> User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 13 Mar 2021, Andrew Morton wrote: > On Fri, 5 Mar 2021 04:18:36 +0000 "Matthew Wilcox (Oracle)" wrote: > > > Our type system does not currently distinguish between tail pages and > > head or single pages. This is a problem because we call compound_head() > > multiple times (and the compiler cannot optimise it out), bloating the > > kernel. It also makes programming hard as it is often unclear whether > > a function operates on an individual page, or an entire compound page. > > > > This patch series introduces the struct folio, which is a type that > > represents an entire compound page. This initial set reduces the kernel > > size by approximately 6kB, although its real purpose is adding > > infrastructure to enable further use of the folio. > > Geeze it's a lot of noise. More things to remember and we'll forever > have a mismash of `page' and `folio' and code everywhere converting > from one to the other. Ongoing addition of folio > accessors/manipulators to overlay the existing page > accessors/manipulators, etc. > > It's unclear to me that it's all really worth it. What feedback have > you seen from others? My own feeling and feedback have been much like yours. I don't get very excited by type safety at this level; and although I protested back when all those compound_head()s got tucked into the *PageFlag() functions, the text size increase was not very much, and I never noticed any adverse performance reports. To me, it's distraction, churn and friction, ongoing for years; but that's just me, and I'm resigned to the possibility that it will go in. Matthew is not alone in wanting to pursue it: let others speak. Hugh