Re: [PATCH 1/3] mm/mempolicy: Use the already fetched local variable

[Aneesh Kumar K . V]

Michal Hocko <mhocko@xxxxxxxx> writes:

> On Tue 20-02-24 15:22:07, Huang, Ying wrote:
> [...]
>> This isn't an issue now, because mpol_misplaced() are always called with
>> PTL held.  And, we can still keep thiscpu local variable.
>
> yes, this is the case but it would be better if we made that assumption
> official by lockdep_assert_held
>

How about this folded into this patch?

2 files changed, 12 insertions(+), 4 deletions(-)
mm/memory.c    |  6 ++++--
mm/mempolicy.c | 10 ++++++++--

modified   mm/memory.c
@@ -4879,9 +4879,11 @@ static vm_fault_t do_fault(struct vm_fault *vmf)
 	return ret;
 }
 
-int numa_migrate_prep(struct folio *folio, struct vm_area_struct *vma,
+int numa_migrate_prep(struct folio *folio, struct vm_fault *vmf,
 		      unsigned long addr, int page_nid, int *flags)
 {
+	struct vm_area_struct *vma = vmf->vma;
+
 	folio_get(folio);
 
 	/* Record the current PID acceesing VMA */
@@ -4893,7 +4895,7 @@ int numa_migrate_prep(struct folio *folio, struct vm_area_struct *vma,
 		*flags |= TNF_FAULT_LOCAL;
 	}
 
-	return mpol_misplaced(folio, vma, addr);
+	return mpol_misplaced(folio, vmf, addr);
 }
 
 static vm_fault_t do_numa_page(struct vm_fault *vmf)
modified   mm/mempolicy.c
@@ -2495,18 +2495,24 @@ static inline bool mpol_preferred_should_numa_migrate(int exec_node, int folio_n
  * Return: NUMA_NO_NODE if the page is in a node that is valid for this
  * policy, or a suitable node ID to allocate a replacement folio from.
  */
-int mpol_misplaced(struct folio *folio, struct vm_area_struct *vma,
+int mpol_misplaced(struct folio *folio, struct vm_fault *vmf,
 		   unsigned long addr)
 {
 	struct mempolicy *pol;
 	pgoff_t ilx;
 	struct zoneref *z;
 	int curnid = folio_nid(folio);
+	struct vm_area_struct *vma = vmf->vma;
 	int thiscpu = raw_smp_processor_id();
-	int thisnid = cpu_to_node(thiscpu);
+	int thisnid = numa_node_id();
 	int polnid = NUMA_NO_NODE;
 	int ret = NUMA_NO_NODE;
 
+	/*
+	 * Make sure ptl is held so that we don't preempt and we
+	 * have a stable smp processor id
+	 */
+	lockdep_assert_held(vmf->ptl);
 	pol = get_vma_policy(vma, addr, folio_order(folio), &ilx);
 	if (!(pol->flags & MPOL_F_MOF))
 		goto out;

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