linux-kernel - Re: [PATCH v2 0/3] Convert 64-bit x86/mm/pat to ptdescs

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Message-ID: <aXsUvOmmUBEjrjGY@kernel.org>
Date: Thu, 29 Jan 2026 10:05:16 +0200
From: Mike Rapoport <rppt@...nel.org>
To: "Vishal Moola (Oracle)" <vishal.moola@...il.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
	akpm@...ux-foundation.org,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2 0/3] Convert 64-bit x86/mm/pat to ptdescs

Hi Vishal,

On Wed, Jan 28, 2026 at 02:40:46PM -0800, Vishal Moola (Oracle) wrote:
> x86/mm/pat should be using ptdescs. One line has already been
> converted to pagetable_free(), while the allocation sites use
> get_free_pages(). This causes issues separately allocating ptdescs
> from struct page.
> 
> These patches convert the allocation/free sites to use ptdescs. In
> the short term, this helps enable Matthew's work to allocate frozen
> pagetables[1]. And in the long term, this will help us cleanly split
> ptdesc allocations from struct page.
> 
> [1] https://lore.kernel.org/linux-mm/20251113140448.1814860-1-willy@infradead.org/
> [2] https://lore.kernel.org/linux-mm/20251020001652.2116669-1-willy@infradead.org/T/#u
> 
> ------
> 
> I've also tested this on a tree that separately allocates ptdescs. That
> didn't find any lingering alloc/free issues.
> 
> I've realized that the pgd_list should also be using ptdescs (for 32bit
> in this file). This can be done in a different patchset since there's
> other users of pgd_list that still need to be converted.

Since Andrew merges cover-letter text into the first commit changelog, some
explanation about pgd_list should be a part of that combined changelog.
 
> Based on current mm-new.
> 
> v2:
>   - Use pagetable_alloc() in populate_pgd() - in patch 2
>   - Rename subject line to specify 64-bit (i.e. 32-bit wasn't converted)
>   - Added reference links to the projects mentioned in the cover letter
> 
> Vishal Moola (Oracle) (3):
>   x86/mm/pat: Convert pte code to use ptdescs
>   x86/mm/pat: Convert pmd code to use ptdescs
>   x86/mm/pat: Convert split_large_page() to use ptdescs
> 
>  arch/x86/mm/pat/set_memory.c | 43 ++++++++++++++++++++----------------
>  1 file changed, 24 insertions(+), 19 deletions(-)
> 
> -- 
> 2.52.0
> 

-- 
Sincerely yours,
Mike.