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

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Message-ID: <CAHk-=wjD8i2zJVQ9SfF2t=_0Fkgy-i5Z=mQjCw36AHvbBTGXyg@mail.gmail.com>
Date:   Mon, 23 Aug 2021 15:06:08 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Matthew Wilcox <willy@...radead.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 Mon, Aug 23, 2021 at 2:25 PM Johannes Weiner <hannes@...xchg.org> wrote:
>
> One one hand, the ambition appears to substitute folio for everything
> that could be a base page or a compound page even inside core MM
> code. Since there are very few places in the MM code that expressly
> deal with tail pages in the first place, this amounts to a conversion
> of most MM code - including the LRU management, reclaim, rmap,
> migrate, swap, page fault code etc. - away from "the page".

Yeah, honestly, I would have preferred to see this done the exact
reverse way: make the rule be that "struct page" is always a head
page, and anything that isn't a head page would be called something
else.

Because, as you say, head pages are the norm. And "folio" may be a
clever term, but it's not very natural. Certainly not at all as
intuitive or common as "page" as a name in the industry.

That said, I see why Willy did it the way he did - it was easier to do
it incrementally the way he did. But I do think it ends up with an end
result that is kind of topsy turvy where the common "this is the core
allocation" being called that odd "folio" thing, and then the simpler
"page" name is for things that almost nobody should even care about.

I'd have personally preferred to call the head page just a "page", and
other pages "subpage" or something like that. I think that would be
much more intuitive than "folio/page".

                  Linus