mm, madvise: fail with ENOMEM when splitting vma will hit max_map_count
If madvise(2) advice will result in the underlying vma being split and
the number of areas mapped by the process will exceed
/proc/sys/vm/max_map_count as a result, return ENOMEM instead of EAGAIN.
EAGAIN is returned by madvise(2) when a kernel resource, such as slab,
is temporarily unavailable. It indicates that userspace should retry
the advice in the near future. This is important for advice such as
MADV_DONTNEED which is often used by malloc implementations to free
memory back to the system: we really do want to free memory back when
madvise(2) returns EAGAIN because slab allocations (for vmas, anon_vmas,
or mempolicies) cannot be allocated.
Encountering /proc/sys/vm/max_map_count is not a temporary failure,
however, so return ENOMEM to indicate this is a more serious issue. A
followup patch to the man page will specify this behavior.
Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1701241431120.42507@chino.kir.corp.google.com
Signed-off-by: David Rientjes <rientjes@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Michael Kerrisk <mtk.manpages@googlemail.com>
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/madvise.c b/mm/madvise.c
index 0012071a6..11fc65f 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -92,14 +92,28 @@
case MADV_MERGEABLE:
case MADV_UNMERGEABLE:
error = ksm_madvise(vma, start, end, behavior, &new_flags);
- if (error)
+ if (error) {
+ /*
+ * madvise() returns EAGAIN if kernel resources, such as
+ * slab, are temporarily unavailable.
+ */
+ if (error == -ENOMEM)
+ error = -EAGAIN;
goto out;
+ }
break;
case MADV_HUGEPAGE:
case MADV_NOHUGEPAGE:
error = hugepage_madvise(vma, &new_flags, behavior);
- if (error)
+ if (error) {
+ /*
+ * madvise() returns EAGAIN if kernel resources, such as
+ * slab, are temporarily unavailable.
+ */
+ if (error == -ENOMEM)
+ error = -EAGAIN;
goto out;
+ }
break;
}
@@ -120,15 +134,37 @@
*prev = vma;
if (start != vma->vm_start) {
- error = split_vma(mm, vma, start, 1);
- if (error)
+ if (unlikely(mm->map_count >= sysctl_max_map_count)) {
+ error = -ENOMEM;
goto out;
+ }
+ error = __split_vma(mm, vma, start, 1);
+ if (error) {
+ /*
+ * madvise() returns EAGAIN if kernel resources, such as
+ * slab, are temporarily unavailable.
+ */
+ if (error == -ENOMEM)
+ error = -EAGAIN;
+ goto out;
+ }
}
if (end != vma->vm_end) {
- error = split_vma(mm, vma, end, 0);
- if (error)
+ if (unlikely(mm->map_count >= sysctl_max_map_count)) {
+ error = -ENOMEM;
goto out;
+ }
+ error = __split_vma(mm, vma, end, 0);
+ if (error) {
+ /*
+ * madvise() returns EAGAIN if kernel resources, such as
+ * slab, are temporarily unavailable.
+ */
+ if (error == -ENOMEM)
+ error = -EAGAIN;
+ goto out;
+ }
}
success:
@@ -136,10 +172,7 @@
* vm_flags is protected by the mmap_sem held in write mode.
*/
vma->vm_flags = new_flags;
-
out:
- if (error == -ENOMEM)
- error = -EAGAIN;
return error;
}