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

From: Rasmus Villemoes
Date: Wed Aug 25 2021 - 05:01:21 EST

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].