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authorDavid Rientjes <rientjes@google.com>2017-02-24 14:58:47 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2017-02-24 17:46:55 -0800
commitdef5efe0376501ef7bd6b53ed061512c142e59aa (patch)
tree46c957c37989924f2a970f09e15fc90d757999bf /Documentation/vm
parent712c604dcdf8186295e2af694adf52c6842ad100 (diff)
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>
Diffstat (limited to 'Documentation/vm')
-rw-r--r--Documentation/vm/ksm.txt4
1 files changed, 4 insertions, 0 deletions
diff --git a/Documentation/vm/ksm.txt b/Documentation/vm/ksm.txt
index 0c64a81d6808..6b0ca7feb135 100644
--- a/Documentation/vm/ksm.txt
+++ b/Documentation/vm/ksm.txt
@@ -38,6 +38,10 @@ the range for whenever the KSM daemon is started; even if the range
cannot contain any pages which KSM could actually merge; even if
MADV_UNMERGEABLE is applied to a range which was never MADV_MERGEABLE.
+If a region of memory must be split into at least one new MADV_MERGEABLE
+or MADV_UNMERGEABLE region, the madvise may return ENOMEM if the process
+will exceed vm.max_map_count (see Documentation/sysctl/vm.txt).
+
Like other madvise calls, they are intended for use on mapped areas of
the user address space: they will report ENOMEM if the specified range
includes unmapped gaps (though working on the intervening mapped areas),