On Mon, Nov 27, 2023 at 11:52:56AM +0000, Alexandru Elisei wrote:

Hi Mike,

I really appreciate you having a look!

On Sat, Nov 25, 2023 at 12:03:22PM +0200, Mike Rapoport wrote:

quoted

On Sun, Nov 19, 2023 at 04:56:58PM +0000, Alexandru Elisei wrote:

quoted

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 <redacted>
---
 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.

I did it this way so an arch won't be able to remove flags set by the MM code.
There's a similar pattern in do_mmap() -> calc_vm_flag_bits() ->
arch_calc_vm_flag_bits().

Ok, just add a sentence about it to the commit message.
 

Thanks,
Alex

quoted

quoted

 		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.

-- 
Sincerely yours,
Mike.

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