Re: [PATCH v2] mm/migrate: move common code to numa_migrate_check (was numa_migrate_prep)

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On 2024/8/9 07:37, Zi Yan wrote:
do_numa_page() and do_huge_pmd_numa_page() share a lot of common code. To
reduce redundancy, move common code to numa_migrate_prep() and rename
the function to numa_migrate_check() to reflect its functionality.

Now do_huge_pmd_numa_page() also checks shared folios to set TNF_SHARED
flag.

Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>

LGTM. Feel free to add:
Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>

---
  mm/huge_memory.c | 29 +++++++++-------------
  mm/internal.h    |  5 ++--
  mm/memory.c      | 63 +++++++++++++++++++++++++-----------------------
  3 files changed, 47 insertions(+), 50 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 4e4364a17e6d..96a52e71d167 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1669,22 +1669,23 @@ static inline bool can_change_pmd_writable(struct vm_area_struct *vma,
  vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
  {
  	struct vm_area_struct *vma = vmf->vma;
-	pmd_t oldpmd = vmf->orig_pmd;
-	pmd_t pmd;
  	struct folio *folio;
  	unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
  	int nid = NUMA_NO_NODE;
-	int target_nid, last_cpupid = (-1 & LAST_CPUPID_MASK);
+	int target_nid, last_cpupid;
+	pmd_t pmd, old_pmd;
  	bool writable = false;
  	int flags = 0;
vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
-	if (unlikely(!pmd_same(oldpmd, *vmf->pmd))) {
+	old_pmd = pmdp_get(vmf->pmd);
+
+	if (unlikely(!pmd_same(old_pmd, vmf->orig_pmd))) {
  		spin_unlock(vmf->ptl);
  		return 0;
  	}
- pmd = pmd_modify(oldpmd, vma->vm_page_prot);
+	pmd = pmd_modify(old_pmd, vma->vm_page_prot);
/*
  	 * Detect now whether the PMD could be writable; this information
@@ -1699,18 +1700,10 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
  	if (!folio)
  		goto out_map;
- /* See similar comment in do_numa_page for explanation */
-	if (!writable)
-		flags |= TNF_NO_GROUP;
-
  	nid = folio_nid(folio);
-	/*
-	 * For memory tiering mode, cpupid of slow memory page is used
-	 * to record page access time.  So use default value.
-	 */
-	if (!folio_use_access_time(folio))
-		last_cpupid = folio_last_cpupid(folio);
-	target_nid = numa_migrate_prep(folio, vmf, haddr, nid, &flags);
+
+	target_nid = numa_migrate_check(folio, vmf, haddr, &flags, writable,
+					&last_cpupid);
  	if (target_nid == NUMA_NO_NODE)
  		goto out_map;
  	if (migrate_misplaced_folio_prepare(folio, vma, target_nid)) {
@@ -1728,7 +1721,7 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
  	} else {
  		flags |= TNF_MIGRATE_FAIL;
  		vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
-		if (unlikely(!pmd_same(oldpmd, *vmf->pmd))) {
+		if (unlikely(!pmd_same(pmdp_get(vmf->pmd), vmf->orig_pmd))) {
  			spin_unlock(vmf->ptl);
  			return 0;
  		}
@@ -1736,7 +1729,7 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
out_map:
  	/* Restore the PMD */
-	pmd = pmd_modify(oldpmd, vma->vm_page_prot);
+	pmd = pmd_modify(pmdp_get(vmf->pmd), vma->vm_page_prot);
  	pmd = pmd_mkyoung(pmd);
  	if (writable)
  		pmd = pmd_mkwrite(pmd, vma);
diff --git a/mm/internal.h b/mm/internal.h
index 52f7fc4e8ac3..fb16e18c9761 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1191,8 +1191,9 @@ void vunmap_range_noflush(unsigned long start, unsigned long end);
void __vunmap_range_noflush(unsigned long start, unsigned long end); -int numa_migrate_prep(struct folio *folio, struct vm_fault *vmf,
-		      unsigned long addr, int page_nid, int *flags);
+int numa_migrate_check(struct folio *folio, struct vm_fault *vmf,
+		      unsigned long addr, int *flags, bool writable,
+		      int *last_cpupid);
void free_zone_device_folio(struct folio *folio);
  int migrate_device_coherent_page(struct page *page);
diff --git a/mm/memory.c b/mm/memory.c
index d9b1dff9dc57..3441f60d54ef 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5368,16 +5368,43 @@ static vm_fault_t do_fault(struct vm_fault *vmf)
  	return ret;
  }
-int numa_migrate_prep(struct folio *folio, struct vm_fault *vmf,
-		      unsigned long addr, int page_nid, int *flags)
+int numa_migrate_check(struct folio *folio, struct vm_fault *vmf,
+		      unsigned long addr, int *flags,
+		      bool writable, int *last_cpupid)
  {
  	struct vm_area_struct *vma = vmf->vma;
+ /*
+	 * Avoid grouping on RO pages in general. RO pages shouldn't hurt as
+	 * much anyway since they can be in shared cache state. This misses
+	 * the case where a mapping is writable but the process never writes
+	 * to it but pte_write gets cleared during protection updates and
+	 * pte_dirty has unpredictable behaviour between PTE scan updates,
+	 * background writeback, dirty balancing and application behaviour.
+	 */
+	if (!writable)
+		*flags |= TNF_NO_GROUP;
+
+	/*
+	 * Flag if the folio is shared between multiple address spaces. This
+	 * is later used when determining whether to group tasks together
+	 */
+	if (folio_likely_mapped_shared(folio) && (vma->vm_flags & VM_SHARED))
+		*flags |= TNF_SHARED;
+	/*
+	 * For memory tiering mode, cpupid of slow memory page is used
+	 * to record page access time.  So use default value.
+	 */
+	if (folio_use_access_time(folio))
+		*last_cpupid = (-1 & LAST_CPUPID_MASK);
+	else
+		*last_cpupid = folio_last_cpupid(folio);
+
  	/* Record the current PID acceesing VMA */
  	vma_set_access_pid_bit(vma);
count_vm_numa_event(NUMA_HINT_FAULTS);
-	if (page_nid == numa_node_id()) {
+	if (folio_nid(folio) == numa_node_id()) {
  		count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
  		*flags |= TNF_FAULT_LOCAL;
  	}
@@ -5479,35 +5506,11 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf)
  	if (!folio || folio_is_zone_device(folio))
  		goto out_map;
- /*
-	 * Avoid grouping on RO pages in general. RO pages shouldn't hurt as
-	 * much anyway since they can be in shared cache state. This misses
-	 * the case where a mapping is writable but the process never writes
-	 * to it but pte_write gets cleared during protection updates and
-	 * pte_dirty has unpredictable behaviour between PTE scan updates,
-	 * background writeback, dirty balancing and application behaviour.
-	 */
-	if (!writable)
-		flags |= TNF_NO_GROUP;
-
-	/*
-	 * Flag if the folio is shared between multiple address spaces. This
-	 * is later used when determining whether to group tasks together
-	 */
-	if (folio_likely_mapped_shared(folio) && (vma->vm_flags & VM_SHARED))
-		flags |= TNF_SHARED;
-
  	nid = folio_nid(folio);
  	nr_pages = folio_nr_pages(folio);
-	/*
-	 * For memory tiering mode, cpupid of slow memory page is used
-	 * to record page access time.  So use default value.
-	 */
-	if (folio_use_access_time(folio))
-		last_cpupid = (-1 & LAST_CPUPID_MASK);
-	else
-		last_cpupid = folio_last_cpupid(folio);
-	target_nid = numa_migrate_prep(folio, vmf, vmf->address, nid, &flags);
+
+	target_nid = numa_migrate_check(folio, vmf, vmf->address, &flags,
+					writable, &last_cpupid);
  	if (target_nid == NUMA_NO_NODE)
  		goto out_map;
  	if (migrate_misplaced_folio_prepare(folio, vma, target_nid)) {




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