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

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Date:   Wed, 25 Aug 2021 17:59:14 -0700
From:   "Darrick J. Wong" <djwong@...nel.org>
To:     Jeff Layton <jlayton@...nel.org>
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 08:03:18AM -0400, Jeff Layton wrote:
> On Wed, 2021-08-25 at 07:32 +0100, 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.
> > 
> 
> Absolutely.  "folio" is no worse than "page", we've just had more time
> to get used to "page".

I /like/ the name 'folio'.  My privileged education :P informed me (when
Matthew talked to me the very first time about this patchset) that it's
a wonderfully flexible word that describes both a collection of various
pages and a single large sheet of paper folded in half.  Or in the case
of x86, folded in half nine times.

That's *exactly* the usage that Matthew is proposing.

English already had a word ready for us to use, so let's use it.

--D

(Well, ok, the one thing I dislike is that my brain keeps typing out
'fileio' instead of 'folio', but it's still better than struct xmoqax or
remembering if we do camel_case or PotholeCase.)

> > > 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.
> 
> Same here. Compound words are especially bad, as newbies will
> continually have to look at whether it's "page_set" or "pageset".
> 
> -- 
> Jeff Layton <jlayton@...nel.org>
>