mempolicy: remove confusing MPOL_MF_LAZY dead code

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.

Link: https://lkml.kernel.org/r/80c9665c-1c3f-17ba-21a3-f6115cebf7d@google.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Tejun heo <tj@kernel.org>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/uapi/linux/mempolicy.h b/include/uapi/linux/mempolicy.h
index 046d0cc..a8963f7 100644 (file)
--- 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 b6461d7..e01d3f8 100644 (file)
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -636,12 +636,6 @@ 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,
@@ -680,14 +674,6 @@ 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.
@@ -1254,9 +1240,6 @@ 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
@@ -1301,7 +1284,6 @@ 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);
                }