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mm, madvise: fail with ENOMEM when splitting vma will hit max_map_count

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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/[email protected]
Signed-off-by: David Rientjes <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Jerome Marchand <[email protected]>
Cc: "Kirill A. Shutemov" <[email protected]>
Cc: Michael Kerrisk <[email protected]>
Cc: Anshuman Khandual <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
David Rientjes 2017-02-24 14:58:47 -08:00 • committed by Linus Torvalds
commit def5efe037
5 changed files with 56 additions and 17 deletions
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8
mm/mmap.c
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@ -2499,11 +2499,11 @@ detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct *vma,
}
/*
* __split_vma() bypasses sysctl_max_map_count checking. We use this on the
* munmap path where it doesn't make sense to fail.
* __split_vma() bypasses sysctl_max_map_count checking. We use this where it
* has already been checked or doesn't make sense to fail.
*/
static int __split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
unsigned long addr, int new_below)
int __split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
unsigned long addr, int new_below)
{
struct vm_area_struct *new;
int err;