linux-kernel - Re: [RFC PATCH 09/12] mm/huge_memory: refactor change_huge

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Message-ID: <aPvIPqEfnxxQ7duJ@gourry-fedora-PF4VCD3F>
Date: Fri, 24 Oct 2025 14:41:02 -0400
From: Gregory Price <gourry@...rry.net>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
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Subject: Re: [RFC PATCH 09/12] mm/huge_memory: refactor change_huge_pmd()
 non-present logic

On Fri, Oct 24, 2025 at 08:41:25AM +0100, Lorenzo Stoakes wrote:
> Similar to copy_huge_pmd(), there is a large mass of open-coded logic for
> the CONFIG_ARCH_ENABLE_THP_MIGRATION non-present entry case that does not
> use thp_migration_supported() consistently.
> 
> Resolve this by separating out this logic and introduce
> change_non_present_huge_pmd().
> 
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> ---
--- >8

> +	if (thp_migration_supported() && is_swap_pmd(*pmd)) {
> +		change_non_present_huge_pmd(mm, addr, pmd, uffd_wp,
> +					    uffd_wp_resolve);

You point out the original code doesn't have thp_migration_supported()

is this a bug? or is it benign and just leads to it failing (nicely)
deeper in the stack?

If it's a bug, maybe this patch should be pulled out ahead of the rest?

~Gregory