[RFC PATCH v4 08/27] mm/ksm: skip KSM for managed-memory folios

[Gregory Price]

Private node folios should not participate in KSM merging by default.
The driver manages the memory lifecycle and KSM's page sharing can
interfere with driver operations.

Extend the existing zone_device checks in get_mergeable_page and
ksm_next_page_pmd_entry to cover private node folios as well.

Signed-off-by: Gregory Price <gourry@xxxxxxxxxx>
---
 mm/ksm.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index 2d89a7c8b4eb..c48e95a6fff9 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -40,6 +40,7 @@
 #include <linux/oom.h>
 #include <linux/numa.h>
 #include <linux/pagewalk.h>
+#include <linux/node_private.h>
 
 #include <asm/tlbflush.h>
 #include "internal.h"
@@ -808,7 +809,7 @@ static struct page *get_mergeable_page(struct ksm_rmap_item *rmap_item)
 
 	folio = folio_walk_start(&fw, vma, addr, 0);
 	if (folio) {
-		if (!folio_is_zone_device(folio) &&
+		if (!folio_is_private_managed(folio) &&
 		    folio_test_anon(folio)) {
 			folio_get(folio);
 			page = fw.page;
@@ -2521,7 +2522,8 @@ static int ksm_next_page_pmd_entry(pmd_t *pmdp, unsigned long addr, unsigned lon
 				goto not_found_unlock;
 			folio = page_folio(page);
 
-			if (folio_is_zone_device(folio) || !folio_test_anon(folio))
+			if (unlikely(folio_is_private_managed(folio)) ||
+			    !folio_test_anon(folio))
 				goto not_found_unlock;
 
 			page += ((addr & (PMD_SIZE - 1)) >> PAGE_SHIFT);
@@ -2545,7 +2547,8 @@ static int ksm_next_page_pmd_entry(pmd_t *pmdp, unsigned long addr, unsigned lon
 			continue;
 		folio = page_folio(page);
 
-		if (folio_is_zone_device(folio) || !folio_test_anon(folio))
+		if (unlikely(folio_is_private_managed(folio)) ||
+		    !folio_test_anon(folio))
 			continue;
 		goto found_unlock;
 	}
-- 
2.53.0