mm: numa: Migrate pages handled during a pmd_numa hinting fault

To say that the PMD handling code was incorrectly transferred from autonuma
is an understatement. The intention was to handle a PMDs worth of pages
in the same fault and effectively batch the taking of the PTL and page
migration. The copied version instead has the impact of clearing a number
of pte_numa PTE entries and whether any page migration takes place depends
on racing. This just happens to work in some cases.

This patch handles pte_numa faults in batch when a pmd_numa fault is
handled. The pages are migrated if they are currently misplaced.
Essentially this is making an assumption that NUMA locality is
on a PMD boundary but that could be addressed by only setting
pmd_numa if all the pages within that PMD are on the same node
if necessary.

Signed-off-by: Mel Gorman <mgorman@suse.de>

2 files changed, 54 insertions, 22 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 8a7b4ccbe136..84c6d9eab182 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3449,6 +3449,18 @@ static int do_nonlinear_fault(struct mm_struct *mm, struct vm_area_struct *vma,
         return __do_fault(mm, vma, address, pmd, pgoff, flags, orig_pte);
 }
 
+int numa_migrate_prep(struct page *page, struct vm_area_struct *vma,
+                                unsigned long addr, int current_nid)
+{
+        get_page(page);
+
+        count_vm_numa_event(NUMA_HINT_FAULTS);
+        if (current_nid == numa_node_id())
+                count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
+
+        return mpol_misplaced(page, vma, addr);
+}
+
 int do_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
                    unsigned long addr, pte_t pte, pte_t *ptep, pmd_t *pmd)
 {
@@ -3477,18 +3489,14 @@ int do_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
         set_pte_at(mm, addr, ptep, pte);
         update_mmu_cache(vma, addr, ptep);
 
-        count_vm_numa_event(NUMA_HINT_FAULTS);
         page = vm_normal_page(vma, addr, pte);
         if (!page) {
                 pte_unmap_unlock(ptep, ptl);
                 return 0;
         }
 
-        get_page(page);
         current_nid = page_to_nid(page);
-        if (current_nid == numa_node_id())
-                count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
-        target_nid = mpol_misplaced(page, vma, addr);
+        target_nid = numa_migrate_prep(page, vma, addr, current_nid);
         pte_unmap_unlock(ptep, ptl);
         if (target_nid == -1) {
                 /*
@@ -3505,7 +3513,8 @@ int do_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
                 current_nid = target_nid;
 
 out:
-        task_numa_fault(current_nid, 1);
+        if (current_nid != -1)
+                task_numa_fault(current_nid, 1);
         return 0;
 }
 
@@ -3521,8 +3530,6 @@ static int do_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
         spinlock_t *ptl;
         bool numa = false;
         int local_nid = numa_node_id();
-        unsigned long nr_faults = 0;
-        unsigned long nr_faults_local = 0;
 
         spin_lock(&mm->page_table_lock);
         pmd = *pmdp;
@@ -3545,7 +3552,8 @@ static int do_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
         for (addr = _addr + offset; addr < _addr + PMD_SIZE; pte++, addr += PAGE_SIZE) {
                 pte_t pteval = *pte;
                 struct page *page;
-                int curr_nid;
+                int curr_nid = local_nid;
+                int target_nid;
                 if (!pte_present(pteval))
                         continue;
                 if (!pte_numa(pteval))
@@ -3566,21 +3574,30 @@ static int do_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
                 /* only check non-shared pages */
                 if (unlikely(page_mapcount(page) != 1))
                         continue;
-                pte_unmap_unlock(pte, ptl);
 
-                curr_nid = page_to_nid(page);
-                task_numa_fault(curr_nid, 1);
+                /*
+                 * Note that the NUMA fault is later accounted to either
+                 * the node that is currently running or where the page is
+                 * migrated to.
+                 */
+                curr_nid = local_nid;
+                target_nid = numa_migrate_prep(page, vma, addr,
+                                               page_to_nid(page));
+                if (target_nid == -1) {
+                        put_page(page);
+                        continue;
+                }
 
-                nr_faults++;
-                if (curr_nid == local_nid)
-                        nr_faults_local++;
+                /* Migrate to the requested node */
+                pte_unmap_unlock(pte, ptl);
+                if (migrate_misplaced_page(page, target_nid))
+                        curr_nid = target_nid;
+                task_numa_fault(curr_nid, 1);
 
                 pte = pte_offset_map_lock(mm, pmdp, addr, &ptl);
         }
         pte_unmap_unlock(orig_pte, ptl);
 
-        count_vm_numa_events(NUMA_HINT_FAULTS, nr_faults);
-        count_vm_numa_events(NUMA_HINT_FAULTS_LOCAL, nr_faults_local);
         return 0;
 }
 #else
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 7ef6ae964e8f..dce6fb48edc4 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -37,12 +37,14 @@ static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
 
 static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
                 unsigned long addr, unsigned long end, pgprot_t newprot,
-                int dirty_accountable, int prot_numa)
+                int dirty_accountable, int prot_numa, bool *ret_all_same_node)
 {
         struct mm_struct *mm = vma->vm_mm;
         pte_t *pte, oldpte;
         spinlock_t *ptl;
         unsigned long pages = 0;
+        bool all_same_node = true;
+        int last_nid = -1;
 
         pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
         arch_enter_lazy_mmu_mode();
@@ -61,6 +63,12 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 
                                 page = vm_normal_page(vma, addr, oldpte);
                                 if (page) {
+                                        int this_nid = page_to_nid(page);
+                                        if (last_nid == -1)
+                                                last_nid = this_nid;
+                                        if (last_nid != this_nid)
+                                                all_same_node = false;
+
                                         /* only check non-shared pages */
                                         if (!pte_numa(oldpte) &&
                                             page_mapcount(page) == 1) {
@@ -81,7 +89,6 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 
                         if (updated)
                                 pages++;
-
                         ptep_modify_prot_commit(mm, addr, pte, ptent);
                 } else if (IS_ENABLED(CONFIG_MIGRATION) && !pte_file(oldpte)) {
                         swp_entry_t entry = pte_to_swp_entry(oldpte);
@@ -101,6 +108,7 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
         arch_leave_lazy_mmu_mode();
         pte_unmap_unlock(pte - 1, ptl);
 
+        *ret_all_same_node = all_same_node;
         return pages;
 }
 
@@ -127,6 +135,7 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma, pud_t *
         pmd_t *pmd;
         unsigned long next;
         unsigned long pages = 0;
+        bool all_same_node;
 
         pmd = pmd_offset(pud, addr);
         do {
@@ -143,9 +152,15 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma, pud_t *
                 if (pmd_none_or_clear_bad(pmd))
                         continue;
                 pages += change_pte_range(vma, pmd, addr, next, newprot,
-                                 dirty_accountable, prot_numa);
-
-                if (prot_numa)
+                                 dirty_accountable, prot_numa, &all_same_node);
+
+                /*
+                 * If we are changing protections for NUMA hinting faults then
+                 * set pmd_numa if the examined pages were all on the same
+                 * node. This allows a regular PMD to be handled as one fault
+                 * and effectively batches the taking of the PTL
+                 */
+                if (prot_numa && all_same_node)
                         change_pmd_protnuma(vma->vm_mm, addr, pmd);
         } while (pmd++, addr = next, addr != end);