linux-kernel - Re: [PATCH RFC 20/29] mm: convert "movable" flag in page->mapping to a page flag

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Message-ID: <2EE119E0-C71C-43C6-A445-E9CB8AAA86E6@nvidia.com>
Date: Mon, 23 Jun 2025 10:14:16 -0400
From: Zi Yan <ziy@...dia.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
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Subject: Re: [PATCH RFC 20/29] mm: convert "movable" flag in page->mapping to
 a page flag

On 18 Jun 2025, at 13:40, David Hildenbrand wrote:

> Instead, let's use a page flag. As the page flag can result in
> false-positives, glue it to the page types for which we
> support/implement movable_ops page migration.
>
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>  include/linux/balloon_compaction.h |  2 +-
>  include/linux/migrate.h            |  8 -----
>  include/linux/page-flags.h         | 52 ++++++++++++++++++++++++------
>  mm/compaction.c                    |  6 ----
>  mm/zpdesc.h                        |  2 +-
>  5 files changed, 44 insertions(+), 26 deletions(-)
>

<snip>

> +
> +/**
> + * page_has_movable_ops - test for a movable_ops page
> + * @page The page to test.
> + *
> + * Test whether this is a movable_ops page. Such pages will stay that
> + * way until freed.
> + *
> + * Returns true if this is a movable_ops page, otherwise false.
> + */
> +static inline bool page_has_movable_ops(const struct page *page)
> +{
> +	return PageMovableOps(page) &&
> +	       (PageOffline(page) || PageZsmalloc(page));
> +}
> +

Should we do the code below in case PageMovableOps is set on pages
other than PageOffline and PageZsmalloc?

return PageMovableOps(page) &&
	   !VM_WARN_ON_ONCE_PAGE(!(PageOffline(page) || PageZsmalloc(page)),
							 page);

>  static __always_inline int PageAnonExclusive(const struct page *page)
>  {
>  	VM_BUG_ON_PGFLAGS(!PageAnon(page), page);
> diff --git a/mm/compaction.c b/mm/compaction.c
> index a10f23df9396e..86d671a520e91 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -114,12 +114,6 @@ static unsigned long release_free_list(struct list_head *freepages)
>  }
>
>  #ifdef CONFIG_COMPACTION
> -void __SetPageMovable(struct page *page)
> -{
> -	VM_BUG_ON_PAGE(!PageLocked(page), page);
> -	page->mapping = (void *)(PAGE_MAPPING_MOVABLE);
> -}
> -EXPORT_SYMBOL(__SetPageMovable);
>
>  /* Do not skip compaction more than 64 times */
>  #define COMPACT_MAX_DEFER_SHIFT 6
> diff --git a/mm/zpdesc.h b/mm/zpdesc.h
> index 6855d9e2732d8..25bf5ea0beb83 100644
> --- a/mm/zpdesc.h
> +++ b/mm/zpdesc.h
> @@ -154,7 +154,7 @@ static inline struct zpdesc *pfn_zpdesc(unsigned long pfn)
>
>  static inline void __zpdesc_set_movable(struct zpdesc *zpdesc)
>  {
> -	__SetPageMovable(zpdesc_page(zpdesc));
> +	SetPageMovableOps(zpdesc_page(zpdesc));
>  }
>
>  static inline void __zpdesc_set_zsmalloc(struct zpdesc *zpdesc)
> -- 
> 2.49.0

Otherwise, LGTM. Reviewed-by: Zi Yan <ziy@...dia.com>

--
Best Regards,
Yan, Zi