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

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Message-ID: <606415b9-27f8-4881-827f-45e8427f46fd@redhat.com>
Date: Mon, 22 Jan 2024 18:40:28 +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 18:34, David Hildenbrand wrote:
> 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

Forgot to delete that sentence.

Anyhow, it's all confusing. My replacement in 91b2978a34807 from 
SetPageDirty -> folio_set_dirty() was correct. It only operates on anon 
folios, likely that's why folio_set_dirty() is okay there.

Oh my.

-- 
Cheers,

David / dhildenb