linux-kernel - Re: [PATCH v4 00/25] Page folios

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Message-Id: <20210313123658.ad2dcf79a113a8619c19c33b@linux-foundation.org>
Date:   Sat, 13 Mar 2021 12:36:58 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v4 00/25] Page folios

On Fri,  5 Mar 2021 04:18:36 +0000 "Matthew Wilcox (Oracle)" <willy@...radead.org> wrote:

> Our type system does not currently distinguish between tail pages and
> head or single pages.  This is a problem because we call compound_head()
> multiple times (and the compiler cannot optimise it out), bloating the
> kernel.  It also makes programming hard as it is often unclear whether
> a function operates on an individual page, or an entire compound page.
> 
> This patch series introduces the struct folio, which is a type that
> represents an entire compound page.  This initial set reduces the kernel
> size by approximately 6kB, although its real purpose is adding
> infrastructure to enable further use of the folio.

Geeze it's a lot of noise.  More things to remember and we'll forever
have a mismash of `page' and `folio' and code everywhere converting
from one to the other.  Ongoing addition of folio
accessors/manipulators to overlay the existing page
accessors/manipulators, etc.

It's unclear to me that it's all really worth it.  What feedback have
you seen from others?