[2/2] mm/mempolicy: do not duplicate policy if it is not applicable for set_mempolicy_home_node

Commit Message

Mathieu Desnoyers Dec. 16, 2022, 7:45 p.m. UTC

From: Michal Hocko <[e-mail]>

set_mempolicy_home_node tries to duplicate a memory policy before
checking it whether it is applicable for the operation. There is
no real reason for doing that and it might actually be a pointless
memory allocation and deallocation exercise for MPOL_INTERLEAVE.

Not a big problem but we can do better. Simply check the policy before
acting on it.

[ Mathieu: compile-tested only. Tested-by would be welcome. ]

Signed-off-by: Michal Hocko <[e-mail]>
Reviewed-by: Mathieu Desnoyers <[e-mail]>
Signed-off-by: Mathieu Desnoyers <[e-mail]>
Cc: Aneesh Kumar K.V <[e-mail]>
Cc: Dave Hansen <[e-mail]>
Cc: Feng Tang <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Andrea Arcangeli <[e-mail]>
Cc: Mel Gorman <[e-mail]>
Cc: Mike Kravetz <[e-mail]>
Cc: Randy Dunlap <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Cc: Andi Kleen <[e-mail]>
Cc: Dan Williams <[e-mail]>
Cc: Huang Ying <[e-mail]>
Cc: [e-mail]
Cc: Andrew Morton <[e-mail]>
Cc: [e-mail]
---
 mm/mempolicy.c | 28 ++++++++++++----------------
 1 file changed, 12 insertions(+), 16 deletions(-)

Patch

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 02c8a712282f..becf41e10076 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1489,7 +1489,7 @@  SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le
 {
 	struct mm_struct *mm = current->mm;
 	struct vm_area_struct *vma;
-	struct mempolicy *new;
+	struct mempolicy *new, *old;
 	unsigned long vmstart;
 	unsigned long vmend;
 	unsigned long end;
@@ -1521,31 +1521,27 @@  SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le
 		return 0;
 	mmap_write_lock(mm);
 	for_each_vma_range(vmi, vma, end) {
-		vmstart = max(start, vma->vm_start);
-		vmend   = min(end, vma->vm_end);
-		new = mpol_dup(vma_policy(vma));
-		if (IS_ERR(new)) {
-			err = PTR_ERR(new);
-			break;
-		}
-		/*
-		 * Only update home node if there is an existing vma policy
-		 */
-		if (!new)
-			continue;
-
 		/*
 		 * If any vma in the range got policy other than MPOL_BIND
 		 * or MPOL_PREFERRED_MANY we return error. We don't reset
 		 * the home node for vmas we already updated before.
 		 */
-		if (new->mode != MPOL_BIND && new->mode != MPOL_PREFERRED_MANY) {
-			mpol_put(new);
+		old = vma_policy(vma);
+		if (!old)
+			continue;
+		if (old->mode != MPOL_BIND && old->mode != MPOL_PREFERRED_MANY) {
 			err = -EOPNOTSUPP;
 			break;
 		}
+		new = mpol_dup(old);
+		if (IS_ERR(new)) {
+			err = PTR_ERR(new);
+			break;
+		}
 
 		new->home_node = home_node;
+		vmstart = max(start, vma->vm_start);
+		vmend   = min(end, vma->vm_end);
 		err = mbind_range(mm, vmstart, vmend, new);
 		mpol_put(new);
 		if (err)