mm: mprotect: convert to folio_can_map_prot_numa()

The prot_numa_skip() naming is not good since it updates the folio access
time except checking whether to skip prot NUMA, so rename it to
folio_can_map_prot_numa(), and cleanup it a bit, remove ret by directly
return value instead of goto style.

Adding a new helper vma_is_single_threaded_private() to check whether it's
a single threaded private VMA, and make folio_can_map_prot_numa() a
non-static function so that they could be reused in change_huge_pmd(),
since folio_can_map_prot_numa() will be shared in different paths, let's
move it near change_prot_numa() in mempolicy.c.

Link: https://lkml.kernel.org/r/20251023113737.3572790-4-wangkefeng.wang@huawei.com
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 61 insertions, 0 deletions

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index eb83cff7db8c..7ae3f5e2dee6 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -85,6 +85,7 @@
 #include <linux/sched.h>
 #include <linux/sched/mm.h>
 #include <linux/sched/numa_balancing.h>
+#include <linux/sched/sysctl.h>
 #include <linux/sched/task.h>
 #include <linux/nodemask.h>
 #include <linux/cpuset.h>
@@ -99,6 +100,7 @@
 #include <linux/swap.h>
 #include <linux/seq_file.h>
 #include <linux/proc_fs.h>
+#include <linux/memory-tiers.h>
 #include <linux/migrate.h>
 #include <linux/ksm.h>
 #include <linux/rmap.h>
@@ -803,6 +805,65 @@ unlock:
 }
 
 #ifdef CONFIG_NUMA_BALANCING
+/**
+ * folio_can_map_prot_numa() - check whether the folio can map prot numa
+ * @folio: The folio whose mapping considered for being made NUMA hintable
+ * @vma: The VMA that the folio belongs to.
+ * @is_private_single_threaded: Is this a single-threaded private VMA or not
+ *
+ * This function checks to see if the folio actually indicates that
+ * we need to make the mapping one which causes a NUMA hinting fault,
+ * as there are cases where it's simply unnecessary, and the folio's
+ * access time is adjusted for memory tiering if prot numa needed.
+ *
+ * Return: True if the mapping of the folio needs to be changed, false otherwise.
+ */
+bool folio_can_map_prot_numa(struct folio *folio, struct vm_area_struct *vma,
+		bool is_private_single_threaded)
+{
+	int nid;
+
+	if (!folio || folio_is_zone_device(folio) || folio_test_ksm(folio))
+		return false;
+
+	/* Also skip shared copy-on-write folios */
+	if (is_cow_mapping(vma->vm_flags) && folio_maybe_mapped_shared(folio))
+		return false;
+
+	/* Folios are pinned and can't be migrated */
+	if (folio_maybe_dma_pinned(folio))
+		return false;
+
+	/*
+	 * While migration can move some dirty folios,
+	 * it cannot move them all from MIGRATE_ASYNC
+	 * context.
+	 */
+	if (folio_is_file_lru(folio) && folio_test_dirty(folio))
+		return false;
+
+	/*
+	 * Don't mess with PTEs if folio is already on the node
+	 * a single-threaded process is running on.
+	 */
+	nid = folio_nid(folio);
+	if (is_private_single_threaded && (nid == numa_node_id()))
+		return false;
+
+	/*
+	 * Skip scanning top tier node if normal numa
+	 * balancing is disabled
+	 */
+	if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_NORMAL) &&
+	    node_is_toptier(nid))
+		return false;
+
+	if (folio_use_access_time(folio))
+		folio_xchg_access_time(folio, jiffies_to_msecs(jiffies));
+
+	return true;
+}
+
 /*
  * This is used to mark a range of virtual addresses to be inaccessible.
  * These are later cleared by a NUMA hinting fault. Depending on these