linux-kernel - [RFC PATCH 1/4] mm: migrate: Allow misplaced migration without VMA too

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Message-ID: <20250306054532.221138-2-bharata@amd.com>
Date: Thu, 6 Mar 2025 11:15:29 +0530
From: Bharata B Rao <bharata@....com>
To: <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
CC: <AneeshKumar.KizhakeVeetil@....com>, <Hasan.Maruf@....com>,
	<Jonathan.Cameron@...wei.com>, <Michael.Day@....com>,
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	<ziy@...dia.com>, <dave@...olabs.net>, <yuanchu@...gle.com>,
	<hyeonggon.yoo@...com>, Bharata B Rao <bharata@....com>
Subject: [RFC PATCH 1/4] mm: migrate: Allow misplaced migration without VMA too

migrate_misplaced_folio_prepare() can be called from a
context where VMA isn't available. Allow the migration
to work from such contexts too.

Signed-off-by: Bharata B Rao <bharata@....com>
---
 mm/migrate.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index fb19a18892c8..5b21856a0dd0 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2639,7 +2639,8 @@ static struct folio *alloc_misplaced_dst_folio(struct folio *src,
 
 /*
  * Prepare for calling migrate_misplaced_folio() by isolating the folio if
- * permitted. Must be called with the PTL still held.
+ * permitted. Must be called with the PTL still held if called with a non-NULL
+ * vma.
  */
 int migrate_misplaced_folio_prepare(struct folio *folio,
 		struct vm_area_struct *vma, int node)
@@ -2656,7 +2657,7 @@ int migrate_misplaced_folio_prepare(struct folio *folio,
 		 * See folio_likely_mapped_shared() on possible imprecision
 		 * when we cannot easily detect if a folio is shared.
 		 */
-		if ((vma->vm_flags & VM_EXEC) &&
+		if (vma && (vma->vm_flags & VM_EXEC) &&
 		    folio_likely_mapped_shared(folio))
 			return -EACCES;
 
-- 
2.34.1