linux-kernel - Re: [PATCH v1 1/2] mm: move pte table reclaim code to memory.c

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Message-ID: <fccb971f-3c7f-4bad-8c2d-6399985eefea@kernel.org>
Date: Wed, 21 Jan 2026 13:08:00 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: Kiryl Shutsemau <kirill@...temov.name>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 Andrew Morton <akpm@...ux-foundation.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka
 <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
 Qi Zheng <qi.zheng@...ux.dev>
Subject: Re: [PATCH v1 1/2] mm: move pte table reclaim code to memory.c

On 1/20/26 12:19, Kiryl Shutsemau wrote:
> On Mon, Jan 19, 2026 at 11:07:07PM +0100, David Hildenbrand (Red Hat) wrote:
>> The pte-table reclaim code is only called from memory.c, while zapping
>> pages, and it better also stays that way in the long run. If we ever
>> have to call it from other files, we should expose proper high-level
>> helpers for zapping if the existing helpers are not good enough.
>>
>> So, let's move the code over (it's not a lot) and slightly clean it up a
>> bit by:
>> - Renaming the functions.
>> - Dropping the "Check if it is empty PTE page" comment, which is now
>>    self-explaining given the function name.
>> - Making zap_pte_table_if_empty() return whether zapping worked so the
>>    caller can free it.
>> - Adding a comment in pte_table_reclaim_possible().
>> - Inlining free_pte() in the last remaining user.
>> - In zap_empty_pte_table(), switch from pmdp_get_lcokless() to
>>    pmd_clear(), we are holding the PMD PT lock.
>>
>> By moving the code over, compilers can also easily figure out when
>> zap_empty_pte_table() does not initialize the pmdval variable, avoiding
>> false-positive warnings about the variable possibly not being
>> initialized.
> 
> mm/memory.c is a kitchen sink as it is.
> 
> I think you miss opportunity to introduce mm/zap.c and move all zap
> code.
> 
> It can be done for code from both mm/memory.c and mm/huge_memory.c.
> Line between THP and non-THP code gets more and more blurry over time.
> 
> The same can be done for copy and fault code. I think it is going to be
> more maintainable this way.

While agree that memory.c contains too much stuff, I don't think zap.c 
is the right abstraction either. And actually, I think basic page table 
handling is well kept in memory.c, or moved along with other stuff 
(fork()) handling somewhere else.

So I won't do any of that as part of this patch.

-- 
Cheers

David