linux-kernel - Re: [PATCH v2 28/40] mm/memory: page_remove_rmap() -> folio_remove_rmap

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Message-ID: <Za6jxXIFjnCnyvPE@casper.infradead.org>
Date: Mon, 22 Jan 2024 17:20:05 +0000
From: Matthew Wilcox <willy@...radead.org>
To: David Hildenbrand <david@...hat.com>
Cc: Ryan Roberts <ryan.roberts@....com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Yin Fengwei <fengwei.yin@...el.com>,
	Mike Kravetz <mike.kravetz@...cle.com>,
	Muchun Song <muchun.song@...ux.dev>, Peter Xu <peterx@...hat.com>
Subject: Re: [PATCH v2 28/40] mm/memory: page_remove_rmap() ->
 folio_remove_rmap_pte()

On Mon, Jan 22, 2024 at 06:01:58PM +0100, David Hildenbrand wrote:
> > And folio_mark_dirty() is doing more than just setting teh PG_dirty bit. In my
> > equivalent change, as part of the contpte series, I've swapped set_page_dirty()
> > for folio_mark_dirty().
> 
> Good catch, that should be folio_mark_dirty(). Let me send a fixup.
> 
> (the difference in naming for both functions really is bad)

It really is, and I don't know what to do about it.

We need a function that literally just sets the flag.  For every other
flag, that's folio_set_FLAG.  We can't use __folio_set_flag because that
means "set the flag non-atomically".

We need a function that does all of the work involved with tracking
dirty folios.  I chose folio_mark_dirty() to align with
folio_mark_uptodate() (ie mark is not just 'set" but also "do some extra
work").

But because we're converting from set_page_dirty(), the OBVIOUS rename
is to folio_set_dirty(), which is WRONG.

So we're in the part of the design space where the consistent naming and
the-obvious-thing-to-do-is-wrong are in collision, and I do not have a
good answer.

Maybe we can call the first function _folio_set_dirty(), and we don't
have a folio_set_dirty() at all?  We don't have a folio_set_uptodate(),
so there's some precedent there.