memory tiering: introduce folio_use_access_time() check

If memory tiering mode is on and a folio is not in the top tier memory,
folio's cpupid field is repurposed to store page access time.  Instead of
an open coded check, use a function to encapsulate the check.

Link: https://lkml.kernel.org/r/20240724130115.793641-3-ziy@nvidia.comSigned-off-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/mm.h

@@ -1745,6 +1745,8 @@ static inline void vma_set_access_pid_bit(struct vm_area_struct *vma)
 		__set_bit(pid_bit, &vma->numab_state->pids_active[1]);
 	}
 }
+
+bool folio_use_access_time(struct folio *folio);
 #else /* !CONFIG_NUMA_BALANCING */
 static inline int folio_xchg_last_cpupid(struct folio *folio, int cpupid)
 {
@@ -1798,6 +1800,10 @@ static inline bool cpupid_match_pid(struct task_struct *task, int cpupid)
 static inline void vma_set_access_pid_bit(struct vm_area_struct *vma)
 {
 }
+static inline bool folio_use_access_time(struct folio *folio)
+{
+	return false;
+}
 #endif /* CONFIG_NUMA_BALANCING */
 
 #if defined(CONFIG_KASAN_SW_TAGS) || defined(CONFIG_KASAN_HW_TAGS)

kernel/sched/fair.c

@@ -1840,8 +1840,7 @@ bool should_numa_migrate_memory(struct task_struct *p, struct folio *folio,
 	 * The pages in slow memory node should be migrated according
 	 * to hot/cold instead of private/shared.
 	 */
-	if (sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING &&
-	    !node_is_toptier(src_nid)) {
+	if (folio_use_access_time(folio)) {
 		struct pglist_data *pgdat;
 		unsigned long rate_limit;
 		unsigned int latency, th, def_th;

mm/huge_memory.c

@@ -1707,8 +1707,7 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
 	 * For memory tiering mode, cpupid of slow memory page is used
 	 * to record page access time.  So use default value.
 	 */
-	if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING) ||
-	    node_is_toptier(nid))
+	if (!folio_use_access_time(folio))
 		last_cpupid = folio_last_cpupid(folio);
 	target_nid = numa_migrate_prep(folio, vmf, haddr, nid, &flags);
 	if (target_nid == NUMA_NO_NODE)
@@ -2058,8 +2057,7 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 		    toptier)
 			goto unlock;
 
-		if (sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING &&
-		    !toptier)
+		if (folio_use_access_time(folio))
 			folio_xchg_access_time(folio,
 					       jiffies_to_msecs(jiffies));
 	}

mm/memory-tiers.c

@@ -6,6 +6,7 @@
 #include <linux/memory.h>
 #include <linux/memory-tiers.h>
 #include <linux/notifier.h>
+#include <linux/sched/sysctl.h>
 
 #include "internal.h"
 
@@ -50,6 +51,24 @@ static const struct bus_type memory_tier_subsys = {
 	.dev_name = "memory_tier",
 };
 
+#ifdef CONFIG_NUMA_BALANCING
+/**
+ * folio_use_access_time - check if a folio reuses cpupid for page access time
+ * @folio: folio to check
+ *
+ * folio's _last_cpupid field is repurposed by memory tiering. In memory
+ * tiering mode, cpupid of slow memory folio (not toptier memory) is used to
+ * record page access time.
+ *
+ * Return: the folio _last_cpupid is used to record page access time
+ */
+bool folio_use_access_time(struct folio *folio)
+{
+	return (sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING) &&
+	       !node_is_toptier(folio_nid(folio));
+}
+#endif
+
 #ifdef CONFIG_MIGRATION
 static int top_tier_adistance;
 /*

mm/memory.c

@@ -5337,8 +5337,7 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf)
 	 * For memory tiering mode, cpupid of slow memory page is used
 	 * to record page access time.  So use default value.
 	 */
-	if ((sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING) &&
-	    !node_is_toptier(nid))
+	if (folio_use_access_time(folio))
 		last_cpupid = (-1 & LAST_CPUPID_MASK);
 	else
 		last_cpupid = folio_last_cpupid(folio);

mm/mprotect.c

@@ -161,8 +161,7 @@ static long change_pte_range(struct mmu_gather *tlb,
 				if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_NORMAL) &&
 				    toptier)
 					continue;
-				if (sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING &&
-				    !toptier)
+				if (folio_use_access_time(folio))
 					folio_xchg_access_time(folio,
 						jiffies_to_msecs(jiffies));
 			}