linux-kernel - Re: [GIT PULL] Memory folios for v5.15

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Message-ID: <CAOQ4uxhOmH8sEmpR=Jaj08r84Jpy3U--59LfKdo9H2O-a7kyrQ@mail.gmail.com>
Date:   Thu, 26 Aug 2021 09:32:28 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Christoph Hellwig <hch@...radead.org>,
        "Theodore Ts'o" <tytso@....edu>,
        Matthew Wilcox <willy@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        David Howells <dhowells@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Linux-MM <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] Memory folios for v5.15

On Wed, Aug 25, 2021 at 12:02 PM Rasmus Villemoes
<linux@...musvillemoes.dk> wrote:
>
> On 25/08/2021 08.32, Christoph Hellwig wrote:
> > On Tue, Aug 24, 2021 at 03:44:48PM -0400, Theodore Ts'o wrote:
> >> The problem is whether we use struct head_page, or folio, or mempages,
> >> we're going to be subsystem users' faces.  And people who are using it
> >> every day will eventually get used to anything, whether it's "folio"
> >> or "xmoqax", we sould give a thought to newcomers to Linux file system
> >> code.  If they see things like "read_folio()", they are going to be
> >> far more confused than "read_pages()" or "read_mempages()".
> >
> > Are they?  It's not like page isn't some randomly made up term
> > as well, just one that had a lot more time to spread.
> >
> >> So if someone sees "kmem_cache_alloc()", they can probably make a
> >> guess what it means, and it's memorable once they learn it.
> >> Similarly, something like "head_page", or "mempages" is going to a bit
> >> more obvious to a kernel newbie.  So if we can make a tiny gesture
> >> towards comprehensibility, it would be good to do so while it's still
> >> easier to change the name.
> >
> > All this sounds really weird to me.  I doubt there is any name that
> > nicely explains "structure used to manage arbitrary power of two
> > units of memory in the kernel" very well.  So I agree with willy here,
> > let's pick something short and not clumsy.  I initially found the folio
> > name a little strange, but working with it I got used to it quickly.
> > And all the other uggestions I've seen s far are significantly worse,
> > especially all the odd compounds with page in it.
> >
>
> A comment from the peanut gallery: I find the name folio completely
> appropriate and easy to understand. Our vocabulary is already strongly
> inspired by words used in the world of printed text: the smallest unit
> of information is a char(acter) [ok, we usually call them bytes], a few
> characters make up a word, there's a number of words to each (cache)
> line, and a number of those is what makes up a page. So obviously a
> folio is something consisting of a few pages.
>
> Are the analogies perfect? Of course not. But they are actually quite
> apt; words, lines and pages don't universally have one size, but they do
> form a natural hierarchy describing how we organize information.
>
> Splitting a word across lines can slow down the reader so should be
> avoided... [sorry, couldn't resist].
>

And if we ever want to manage page cache using an arbitrary number
of contiguous filios, we can always saw them into a scroll ;-)

Thanks,
Amir.