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Date:   Thu, 26 Aug 2021 14:02:11 +1000
From:   Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [GIT PULL] Memory folios for v5.15
To:     Christoph Hellwig <hch@infradead.org>,
        Theodore Ts'o <tytso@mit.edu>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        David Howells <dhowells@redhat.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Matthew Wilcox <willy@infradead.org>
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Excerpts from Christoph Hellwig's message of August 25, 2021 4:32 pm:
> 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()".
>=20
> 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.
>=20
>> 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.
>=20
> 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.

Cluster is easily understandable to a filesystem developer as contiguous=20
set of one or more, probably aligned and sized to power of 2.  Swap=20
subsystem in mm uses it (maybe because it's disk adjacent, but it does=20
have page clusters) so mm developers would be fine with it too. Sadly
you might have to call it page_cluster to avoid confusion with block=20
clusters in fs then it gets a bit long.

Superpage could be different enough from huge page that implies one page=20
of a particular large size (even though some other OS might use it for=20
that), but a super set of pages, which could be 1 or more.

Thanks,
Nick