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

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Message-ID: <7214a9f5-367c-492c-b1bd-80bdc9b7ba4c@redhat.com>
Date: Mon, 22 Jan 2024 18:34:15 +0100
From: David Hildenbrand <david@...hat.com>
To: Matthew Wilcox <willy@...radead.org>
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 22.01.24 18:20, Matthew Wilcox wrote:
> 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.

And I made the same mistake at least also in "mm/huge_memory: 
page_remove_rmap() -> folio_remove_rmap_pmd()".

I better double check all these so-simple-looking conversions that just 
went upstream.

Interestingly, __split_huge_pmd_locked() used SetPageReferenced() 
instead of

> 
> 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.

Good question. This mark vs. set is confusing. We want some way to 
highlight that folio_set_dirty() is the one that we usually do not want 
to use.

-- 
Cheers,

David / dhildenb