Re: [PATCH 2/2] migrate: Replace RMP_ flags with TTU_ flags

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

On Fri, Jan 09, 2026 at 04:13:43AM +0000, Matthew Wilcox (Oracle) wrote:
> Instead of translating between RMP_ and TTU_ flags, remove the RMP_
> flags and just use the TTU_ flag space; there's plenty available.
>
> Possibly we should rename these to RMAP_ flags, and maybe even pass them
> in through rmap_walk_arg, but that can be done later.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

LGTM to me, so:

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

> ---
>  include/linux/rmap.h |  9 +++------
>  mm/huge_memory.c     |  8 ++++----
>  mm/migrate.c         | 12 ++++++------
>  3 files changed, 13 insertions(+), 16 deletions(-)
>
> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> index daa92a58585d..7afc6abe1c23 100644
> --- a/include/linux/rmap.h
> +++ b/include/linux/rmap.h
> @@ -92,6 +92,7 @@ struct anon_vma_chain {
>  };
>
>  enum ttu_flags {
> +	TTU_USE_SHARED_ZEROPAGE	= 0x2,	/* for unused pages of large folios */

Kinda weird we had 0x2 free :) I wonder why? Did we have flags here we removed I
guess?

>  	TTU_SPLIT_HUGE_PMD	= 0x4,	/* split huge PMD if any */
>  	TTU_IGNORE_MLOCK	= 0x8,	/* ignore mlock */
>  	TTU_SYNC		= 0x10,	/* avoid racy checks with PVMW_SYNC */
> @@ -1000,12 +1001,8 @@ int mapping_wrprotect_range(struct address_space *mapping, pgoff_t pgoff,
>  int pfn_mkclean_range(unsigned long pfn, unsigned long nr_pages, pgoff_t pgoff,
>  		      struct vm_area_struct *vma);
>
> -enum rmp_flags {
> -	RMP_LOCKED		= 1 << 0,
> -	RMP_USE_SHARED_ZEROPAGE	= 1 << 1,
> -};
> -
> -void remove_migration_ptes(struct folio *src, struct folio *dst, int flags);
> +void remove_migration_ptes(struct folio *src, struct folio *dst,
> +		enum ttu_flags flags);
>
>  /*
>   * rmap_walk_control: To control rmap traversing for specific needs
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 40cf59301c21..44ff8a648afd 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -3431,7 +3431,7 @@ static void remap_page(struct folio *folio, unsigned long nr, int flags)
>  	if (!folio_test_anon(folio))
>  		return;
>  	for (;;) {
> -		remove_migration_ptes(folio, folio, RMP_LOCKED | flags);
> +		remove_migration_ptes(folio, folio, TTU_RMAP_LOCKED | flags);
>  		i += folio_nr_pages(folio);
>  		if (i >= nr)
>  			break;
> @@ -3944,7 +3944,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
>  	int old_order = folio_order(folio);
>  	struct folio *new_folio, *next;
>  	int nr_shmem_dropped = 0;
> -	int remap_flags = 0;
> +	enum ttu_flags ttu_flags = 0;
>  	int ret;
>  	pgoff_t end = 0;
>
> @@ -4064,9 +4064,9 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
>  		shmem_uncharge(mapping->host, nr_shmem_dropped);
>
>  	if (!ret && is_anon && !folio_is_device_private(folio))
> -		remap_flags = RMP_USE_SHARED_ZEROPAGE;
> +		ttu_flags = TTU_USE_SHARED_ZEROPAGE;
>
> -	remap_page(folio, 1 << old_order, remap_flags);
> +	remap_page(folio, 1 << old_order, ttu_flags);
>
>  	/*
>  	 * Unlock all after-split folios except the one containing
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 4688b9e38cd2..4750a2ba15fe 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -452,11 +452,12 @@ static bool remove_migration_pte(struct folio *folio,
>   * Get rid of all migration entries and replace them by
>   * references to the indicated page.
>   */
> -void remove_migration_ptes(struct folio *src, struct folio *dst, int flags)
> +void remove_migration_ptes(struct folio *src, struct folio *dst,
> +		enum ttu_flags flags)
>  {
>  	struct rmap_walk_arg rmap_walk_arg = {
>  		.folio = src,
> -		.map_unused_to_zeropage = flags & RMP_USE_SHARED_ZEROPAGE,
> +		.map_unused_to_zeropage = flags & TTU_USE_SHARED_ZEROPAGE,
>  	};
>
>  	struct rmap_walk_control rwc = {
> @@ -464,9 +465,9 @@ void remove_migration_ptes(struct folio *src, struct folio *dst, int flags)
>  		.arg = &rmap_walk_arg,
>  	};
>
> -	VM_BUG_ON_FOLIO((flags & RMP_USE_SHARED_ZEROPAGE) && (src != dst), src);
> +	VM_BUG_ON_FOLIO((flags & TTU_USE_SHARED_ZEROPAGE) && (src != dst), src);
>
> -	if (flags & RMP_LOCKED)
> +	if (flags & TTU_RMAP_LOCKED)
>  		rmap_walk_locked(dst, &rwc);
>  	else
>  		rmap_walk(dst, &rwc);
> @@ -1521,8 +1522,7 @@ static int unmap_and_move_huge_page(new_folio_t get_new_folio,
>  		rc = move_to_new_folio(dst, src, mode);
>
>  	if (page_was_mapped)
> -		remove_migration_ptes(src, !rc ? dst : src,
> -				ttu ? RMP_LOCKED : 0);
> +		remove_migration_ptes(src, !rc ? dst : src, ttu);
>
>  	if (ttu & TTU_RMAP_LOCKED)
>  		i_mmap_unlock_write(mapping);
> --
> 2.47.3
>
>