linux-kernel - [RFC PATCH v1 1/4] mm: migrate: Allow misplaced migration without VMA too

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Message-ID: <20250616133931.206626-2-bharata@amd.com>
Date: Mon, 16 Jun 2025 19:09:28 +0530
From: Bharata B Rao <bharata@....com>
To: <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
CC: <Jonathan.Cameron@...wei.com>, <dave.hansen@...el.com>,
	<gourry@...rry.net>, <hannes@...xchg.org>, <mgorman@...hsingularity.net>,
	<mingo@...hat.com>, <peterz@...radead.org>, <raghavendra.kt@....com>,
	<riel@...riel.com>, <rientjes@...gle.com>, <sj@...nel.org>,
	<weixugc@...gle.com>, <willy@...radead.org>, <ying.huang@...ux.alibaba.com>,
	<ziy@...dia.com>, <dave@...olabs.net>, <nifan.cxl@...il.com>,
	<xuezhengchu@...wei.com>, <yiannis@...corp.com>, <akpm@...ux-foundation.org>,
	<david@...hat.com>, <bharata@....com>
Subject: [RFC PATCH v1 1/4] mm: migrate: Allow misplaced migration without VMA too

We want isolation of misplaced folios to work in contexts
where VMA isn't available. In order to prepare for that
allow migrate_misplaced_folio_prepare() to be called with
a NULL VMA.

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 8cf0f9c9599d..9fdc2cc3dd1c 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2580,7 +2580,8 @@ 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)
@@ -2597,7 +2598,7 @@ int migrate_misplaced_folio_prepare(struct folio *folio,
 		 * See folio_maybe_mapped_shared() on possible imprecision
 		 * when we cannot easily detect if a folio is shared.
 		 */
-		if ((vma->vm_flags & VM_EXEC) && folio_maybe_mapped_shared(folio))
+		if (vma && (vma->vm_flags & VM_EXEC) && folio_maybe_mapped_shared(folio))
 			return -EACCES;
 
 		/*
-- 
2.34.1