mm: numa: disable change protection for vma(VM_HUGETLB)

Currently when a process accesses a hugetlb range protected with
PROTNONE, unexpected COWs are triggered, which finally puts the hugetlb
subsystem into a broken/uncontrollable state, where for example
h->resv_huge_pages is subtracted too much and wraps around to a very
large number, and the free hugepage pool is no longer maintainable.

This patch simply stops changing protection for vma(VM_HUGETLB) to fix
the problem.  And this also allows us to avoid useless overhead of minor
faults.

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Suggested-by: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bcfe32088b3768363c2f37502a953b61a361f7ff..241213be507cdb4ee569cdaeb4434a53ee9172ea 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2165,8 +2165,10 @@ void task_numa_work(struct callback_head *work)
                vma = mm->mmap;
        }
        for (; vma; vma = vma->vm_next) {
-               if (!vma_migratable(vma) || !vma_policy_mof(vma))
+               if (!vma_migratable(vma) || !vma_policy_mof(vma) ||
+                       is_vm_hugetlb_page(vma)) {
                        continue;
+               }
 
                /*
                 * Shared library pages mapped by multiple processes are not