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[79.242.63.113]) by smtp.gmail.com with ESMTPSA id g136sm4891862wmg.30.2021.09.01.03.18.05 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 01 Sep 2021 03:18:06 -0700 (PDT) To: David Howells , torvalds@linux-foundation.org, Andrew Morton , Johannes Weiner Cc: Matthew Wilcox , Theodore Ts'o , Christoph Hellwig , Alexander Viro , Vlastimil Babka , Rasmus Villemoes , "Darrick J. Wong" , Dan Williams , Jeff Layton , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org References: <3285174.1630448147@warthog.procyon.org.uk> From: David Hildenbrand Organization: Red Hat Subject: Re: Folios: Can we resolve this please? Message-ID: <01ed765d-449d-fa5f-2f08-1b74e7f6a9c8@redhat.com> Date: Wed, 1 Sep 2021 12:18:04 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <3285174.1630448147@warthog.procyon.org.uk> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01.09.21 00:15, David Howells wrote: > Hi Linus, Andrew, Johannes, > > Can we come to a quick resolution on folios? I'd really like this to be > solved in this merge window if at all possible as I (and others) have stuff > that will depend on and will conflict with Willy's folio work. It would be > great to get this sorted one way or another. > > As I see it, there are three issues, I think, and I think they kind of go like > this: > > (1) Johannes wants to get away from pages being used as the unit of memory > currency and thinks that folios aren't helpful in this regard[1]. There > seems to be some disagreement about where this is heading. > > (2) Linus isn't entirely keen on Willy's approach[2], with a bottom up > approach hiding the page objects behind a new type from the pov of the > filesystem, but would rather see the page struct stay the main API type > and the changes be hidden transparently inside of that. > > I think from what Linus said, he may be in favour (if that's not too > strong a word) of using a new type to make sure we don't miss the > necessary changes[3]. > > (3) Linus isn't in favour of the name 'folio' for the new type[2]. Various > names have been bandied around and Linus seems okay with "pageset"[4], > though it's already in minor(-ish) use[5][6]. Willy has an alternate > patchset with "folio" changed to "pageset"[7]. > > With regard to (1), I think the folio concept could be used in future to hide > at least some of the paginess from filesystems. > > With regard to (2), I think a top-down approach won't work until and unless we > wrap all accesses to struct page by filesystems (and device drivers) in > wrapper functions - we need to stop filesystems fiddling with page internals > because what page internals may mean may change. > > With regard to (3), I'm personally fine with the name "folio", as are other > people[8][9][10][11], but I could also live with a conversion to "pageset". > > Is it possible to take the folios patchset as-is and just live with the name, > or just take Willy's rename-job (although it hasn't had linux-next soak time > yet)? Or is the approach fundamentally flawed and in need of redoing? Whatever we do, it would be great to get it out of -next one way (merge) or the other (drop) ASAP, as it's a lot of code churn, affecting various subsystems. But merging it in a (for some people) suboptimal state just to get it out of -next might not necessarily be what we want. -- Thanks, David / dhildenb