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

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Message-ID: <aW9i3Er3HXzg9V7C@thinkstation>
Date: Tue, 20 Jan 2026 11:19:47 +0000
From: Kiryl Shutsemau <kirill@...temov.name>
To: "David Hildenbrand (Red Hat)" <david@...nel.org>
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 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.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov