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@redhat.com>
Signed-off-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
 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 666fa675e5b6..f2fd3aabb67b 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)) {
@@ -1730,13 +1723,13 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
 
 	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;
 	}
 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 bf791da57cab..e4f27c0696cb 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)) {
-- 
2.43.0

On 09.08.24 16:59, 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.

Yeah, I was also wondering why we didn't check that in the PMD case.

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb

David Hildenbrand <david@redhat.com> writes:

> On 09.08.24 16:59, 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.
>
> Yeah, I was also wondering why we didn't check that in the PMD case.

IIUC, before commit 728be28fae8c ("mm: migrate: remove THP mapcount
check in numamigrate_isolate_page()"), we don't allow to migrate THP
with mapcount > 1.  So, it's unnecessary to set TNF_SHARED flag at that
time.  However, after that commit, we need to do it.

--
Best Regards,
Huang, Ying

On 12.08.24 04:20, Huang, Ying wrote:
> David Hildenbrand <david@redhat.com> writes:
> 
>> On 09.08.24 16:59, 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.
>>
>> Yeah, I was also wondering why we didn't check that in the PMD case.
> 
> IIUC, before commit 728be28fae8c ("mm: migrate: remove THP mapcount
> check in numamigrate_isolate_page()"), we don't allow to migrate THP
> with mapcount > 1.  So, it's unnecessary to set TNF_SHARED flag at that
> time.  However, after that commit, we need to do it.

Thanks for the pointer, rings a bell. Indeed, the check was remove for a 
different purpose, so introducing a check for setting the flag makes sense.

-- 
Cheers,

David / dhildenb