diff mbox series

[08/12] mempolicy: remove confusing MPOL_MF_LAZY dead code

Message ID 2cb8b08a-a96c-2a61-94dd-4cd51ad0605d@google.com (mailing list archive)
State New
Headers show
Series mempolicy: cleanups leading to NUMA mpol without vma | expand

Commit Message

Hugh Dickins Sept. 25, 2023, 8:30 a.m. UTC 
v3.8 commit b24f53a0bea3 ("mm: mempolicy: Add MPOL_MF_LAZY") introduced
MPOL_MF_LAZY, and included it in the MPOL_MF_VALID flags; but a720094ded8
("mm: mempolicy: Hide MPOL_NOOP and MPOL_MF_LAZY from userspace for now")
immediately removed it from MPOL_MF_VALID flags, pending further review.
"This will need to be revisited", but it has not been reinstated.

The present state is confusing: there is dead code in mm/mempolicy.c to
handle MPOL_MF_LAZY cases which can never occur.  Remove that: it can be
resurrected later if necessary.  But keep the definition of MPOL_MF_LAZY,
which must remain in the UAPI, even though it always fails with EINVAL.

https://lore.kernel.org/linux-mm/1553041659-46787-1-git-send-email-yang.shi@linux.alibaba.com/
links to a previous request to remove MPOL_MF_LAZY.

Signed-off-by: Hugh Dickins <hughd@google.com>
---
 include/uapi/linux/mempolicy.h |  2 +-
 mm/mempolicy.c                 | 18 ------------------
 2 files changed, 1 insertion(+), 19 deletions(-)

Comments

Matthew Wilcox Sept. 25, 2023, 10:52 p.m. UTC | #1 
On Mon, Sep 25, 2023 at 01:30:51AM -0700, Hugh Dickins wrote:
> v3.8 commit b24f53a0bea3 ("mm: mempolicy: Add MPOL_MF_LAZY") introduced
> MPOL_MF_LAZY, and included it in the MPOL_MF_VALID flags; but a720094ded8
> ("mm: mempolicy: Hide MPOL_NOOP and MPOL_MF_LAZY from userspace for now")
> immediately removed it from MPOL_MF_VALID flags, pending further review.
> "This will need to be revisited", but it has not been reinstated.
> 
> The present state is confusing: there is dead code in mm/mempolicy.c to
> handle MPOL_MF_LAZY cases which can never occur.  Remove that: it can be
> resurrected later if necessary.  But keep the definition of MPOL_MF_LAZY,
> which must remain in the UAPI, even though it always fails with EINVAL.
> 
> https://lore.kernel.org/linux-mm/1553041659-46787-1-git-send-email-yang.shi@linux.alibaba.com/
> links to a previous request to remove MPOL_MF_LAZY.
> 
> Signed-off-by: Hugh Dickins <hughd@google.com>

Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
diff mbox series

Patch

diff --git a/include/uapi/linux/mempolicy.h b/include/uapi/linux/mempolicy.h
index 046d0ccba4cd..a8963f7ef4c2 100644
--- a/include/uapi/linux/mempolicy.h
+++ b/include/uapi/linux/mempolicy.h
@@ -48,7 +48,7 @@  enum {
 #define MPOL_MF_MOVE	 (1<<1)	/* Move pages owned by this process to conform
 				   to policy */
 #define MPOL_MF_MOVE_ALL (1<<2)	/* Move every page to conform to policy */
-#define MPOL_MF_LAZY	 (1<<3)	/* Modifies '_MOVE:  lazy migrate on fault */
+#define MPOL_MF_LAZY	 (1<<3)	/* UNSUPPORTED FLAG: Lazy migrate on fault */
 #define MPOL_MF_INTERNAL (1<<4)	/* Internal flags start here */
 
 #define MPOL_MF_VALID	(MPOL_MF_STRICT   | 	\
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index a22b641cfd6b..7ab6102d7da4 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -632,12 +632,6 @@  unsigned long change_prot_numa(struct vm_area_struct *vma,
 
 	return nr_updated;
 }
-#else
-static unsigned long change_prot_numa(struct vm_area_struct *vma,
-			unsigned long addr, unsigned long end)
-{
-	return 0;
-}
 #endif /* CONFIG_NUMA_BALANCING */
 
 static int queue_pages_test_walk(unsigned long start, unsigned long end,
@@ -676,14 +670,6 @@  static int queue_pages_test_walk(unsigned long start, unsigned long end,
 	if (endvma > end)
 		endvma = end;
 
-	if (flags & MPOL_MF_LAZY) {
-		/* Similar to task_numa_work, skip inaccessible VMAs */
-		if (!is_vm_hugetlb_page(vma) && vma_is_accessible(vma) &&
-			!(vma->vm_flags & VM_MIXEDMAP))
-			change_prot_numa(vma, start, endvma);
-		return 1;
-	}
-
 	/*
 	 * Check page nodes, and queue pages to move, in the current vma.
 	 * But if no moving, and no strict checking, the scan can be skipped.
@@ -1271,9 +1257,6 @@  static long do_mbind(unsigned long start, unsigned long len,
 	if (IS_ERR(new))
 		return PTR_ERR(new);
 
-	if (flags & MPOL_MF_LAZY)
-		new->flags |= MPOL_F_MOF;
-
 	/*
 	 * If we are using the default policy then operation
 	 * on discontinuous address spaces is okay after all
@@ -1318,7 +1301,6 @@  static long do_mbind(unsigned long start, unsigned long len,
 
 	if (!err) {
 		if (!list_empty(&pagelist)) {
-			WARN_ON_ONCE(flags & MPOL_MF_LAZY);
 			nr_failed |= migrate_pages(&pagelist, new_folio, NULL,
 				start, MIGRATE_SYNC, MR_MEMPOLICY_MBIND, NULL);
 		}