Re: [PATCH RFC v2 04/27] mm: migrate/mempolicy: Add hook to modify migration target gfp

Mike Rapoport
2023-11-25T10:04:14Z

On Sun, Nov 19, 2023 at 04:56:58PM +0000, Alexandru Elisei wrote:
> It might be desirable for an architecture to modify the gfp flags used to
> allocate the destination page for migration based on the page that it is
> being replaced. For example, if an architectures has metadata associated
> with a page (like arm64, when the memory tagging extension is implemented),
> it can request that the destination page similarly has storage for tags
> already allocated.
>
> No functional change.
>
> Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
> ---
> include/linux/migrate.h | 4 ++++
> mm/mempolicy.c | 2 ++
> mm/migrate.c | 3 +++
> 3 files changed, 9 insertions(+)
>
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index 2ce13e8a309b..0acef592043c 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -60,6 +60,10 @@ struct movable_operations {
> /* Defined in mm/debug.c: */
> extern const char *migrate_reason_names[MR_TYPES];
>
> +#ifndef arch_migration_target_gfp
> +#define arch_migration_target_gfp(src, gfp) 0
> +#endif
> +
> #ifdef CONFIG_MIGRATION
>
> void putback_movable_pages(struct list_head *l);
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 10a590ee1c89..50bc43ab50d6 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1182,6 +1182,7 @@ static struct folio *alloc_migration_target_by_mpol(struct folio *src,
>
> h = folio_hstate(src);
> gfp = htlb_alloc_mask(h);
> + gfp |= arch_migration_target_gfp(src, gfp);

I think it'll be more robust to have arch_migration_target_gfp() to modify
the flags and return the new mask with added (or potentially removed)
flags.

> nodemask = policy_nodemask(gfp, pol, ilx, &nid);
> return alloc_hugetlb_folio_nodemask(h, nid, nodemask, gfp);
> }
> @@ -1190,6 +1191,7 @@ static struct folio *alloc_migration_target_by_mpol(struct folio *src,
> gfp = GFP_TRANSHUGE;
> else
> gfp = GFP_HIGHUSER_MOVABLE | __GFP_RETRY_MAYFAIL | __GFP_COMP;
> + gfp |= arch_migration_target_gfp(src, gfp);
>
> page = alloc_pages_mpol(gfp, order, pol, ilx, nid);
> return page_rmappable_folio(page);

--
Sincerely yours,
Mike.