Re: [PATCH v1 15/29] mm/migration: remove PageMovable()

Lorenzo Stoakes
2025-07-01T10:51:59Z

On Mon, Jun 30, 2025 at 02:59:56PM +0200, David Hildenbrand wrote:
> As __ClearPageMovable() is gone that would have only made
> PageMovable()==false but still __PageMovable()==true, now
> PageMovable() == __PageMovable().

I think this could be rephrased to be clearer, something like:

Previously, if __ClearPageMovable() were invoked on a page, this would
cause __PageMovable() to return false, but due to the continued
existance of page movable ops, PageMovable() would have returned true.

With __ClearPageMovable() gone, the two are exactly equivalent.

>
> So we can replace PageMovable() checks by __PageMovable(). In fact,
> __PageMovable() cannot change until a page is freed, so we can turn
> some PageMovable() into sanity checks for __PageMovable().

Deferring the clear does seem to simplify things!

>
> Reviewed-by: Zi Yan <ziy@nvidia.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

LGTM, so:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

> ---
> include/linux/migrate.h | 2 --
> mm/compaction.c | 15 ---------------
> mm/migrate.c | 18 ++++++++++--------
> 3 files changed, 10 insertions(+), 25 deletions(-)
>
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index 6eeda8eb1e0d8..25659a685e2aa 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -104,10 +104,8 @@ static inline int migrate_huge_page_move_mapping(struct address_space *mapping,
> #endif /* CONFIG_MIGRATION */
>
> #ifdef CONFIG_COMPACTION
> -bool PageMovable(struct page *page);
> void __SetPageMovable(struct page *page, const struct movable_operations *ops);
> #else
> -static inline bool PageMovable(struct page *page) { return false; }
> static inline void __SetPageMovable(struct page *page,
> const struct movable_operations *ops)
> {
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 889ec696ba96a..5c37373017014 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -114,21 +114,6 @@ static unsigned long release_free_list(struct list_head *freepages)
> }
>
> #ifdef CONFIG_COMPACTION
> -bool PageMovable(struct page *page)
> -{
> - const struct movable_operations *mops;
> -
> - VM_BUG_ON_PAGE(!PageLocked(page), page);
> - if (!__PageMovable(page))
> - return false;
> -
> - mops = page_movable_ops(page);
> - if (mops)
> - return true;
> -
> - return false;
> -}
> -
> void __SetPageMovable(struct page *page, const struct movable_operations *mops)
> {
> VM_BUG_ON_PAGE(!PageLocked(page), page);
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 22c115710d0e2..040484230aebc 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -87,9 +87,12 @@ bool isolate_movable_ops_page(struct page *page, isolate_mode_t mode)
> goto out;
>
> /*
> - * Check movable flag before taking the page lock because
> + * Check for movable_ops pages before taking the page lock because
> * we use non-atomic bitops on newly allocated page flags so
> * unconditionally grabbing the lock ruins page's owner side.
> + *
> + * Note that once a page has movable_ops, it will stay that way
> + * until the page was freed.
> */
> if (unlikely(!__PageMovable(page)))
> goto out_putfolio;
> @@ -108,7 +111,8 @@ bool isolate_movable_ops_page(struct page *page, isolate_mode_t mode)
> if (unlikely(!folio_trylock(folio)))
> goto out_putfolio;
>
> - if (!PageMovable(page) || PageIsolated(page))
> + VM_WARN_ON_ONCE_PAGE(!__PageMovable(page), page);
> + if (PageIsolated(page))
> goto out_no_isolated;
>
> mops = page_movable_ops(page);
> @@ -149,11 +153,10 @@ static void putback_movable_ops_page(struct page *page)
> */
> struct folio *folio = page_folio(page);
>
> + VM_WARN_ON_ONCE_PAGE(!__PageMovable(page), page);
> VM_WARN_ON_ONCE_PAGE(!PageIsolated(page), page);
> folio_lock(folio);
> - /* If the page was released by it's owner, there is nothing to do. */
> - if (PageMovable(page))
> - page_movable_ops(page)->putback_page(page);
> + page_movable_ops(page)->putback_page(page);
> ClearPageIsolated(page);
> folio_unlock(folio);
> folio_put(folio);
> @@ -189,10 +192,9 @@ static int migrate_movable_ops_page(struct page *dst, struct page *src,
> {
> int rc = MIGRATEPAGE_SUCCESS;
>
> + VM_WARN_ON_ONCE_PAGE(!__PageMovable(src), src);
> VM_WARN_ON_ONCE_PAGE(!PageIsolated(src), src);
> - /* If the page was released by it's owner, there is nothing to do. */
> - if (PageMovable(src))
> - rc = page_movable_ops(src)->migrate_page(dst, src, mode);
> + rc = page_movable_ops(src)->migrate_page(dst, src, mode);
> if (rc == MIGRATEPAGE_SUCCESS)
> ClearPageIsolated(src);
> return rc;
> --
> 2.49.0
>