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authorRafael Aquini <aquini@linux.com>2011-06-15 15:08:39 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-06-15 20:04:01 -0700
commitb0320c7b7d1ac1bd5c2d9dff3258524ab39bad32 (patch)
treebdac09caec787a28b1b31fea3c2911808e9cb6d1
parent959ecc48fc7506b9d7825ea70e40d92d9b308033 (diff)
mm: fix negative commitlimit when gigantic hugepages are allocated
When 1GB hugepages are allocated on a system, free(1) reports less available memory than what really is installed in the box. Also, if the total size of hugepages allocated on a system is over half of the total memory size, CommitLimit becomes a negative number. The problem is that gigantic hugepages (order > MAX_ORDER) can only be allocated at boot with bootmem, thus its frames are not accounted to 'totalram_pages'. However, they are accounted to hugetlb_total_pages() What happens to turn CommitLimit into a negative number is this calculation, in fs/proc/meminfo.c: allowed = ((totalram_pages - hugetlb_total_pages()) * sysctl_overcommit_ratio / 100) + total_swap_pages; A similar calculation occurs in __vm_enough_memory() in mm/mmap.c. Also, every vm statistic which depends on 'totalram_pages' will render confusing values, as if system were 'missing' some part of its memory. Impact of this bug: When gigantic hugepages are allocated and sysctl_overcommit_memory == OVERCOMMIT_NEVER. In a such situation, __vm_enough_memory() goes through the mentioned 'allowed' calculation and might end up mistakenly returning -ENOMEM, thus forcing the system to start reclaiming pages earlier than it would be ususal, and this could cause detrimental impact to overall system's performance, depending on the workload. Besides the aforementioned scenario, I can only think of this causing annoyances with memory reports from /proc/meminfo and free(1). [akpm@linux-foundation.org: standardize comment layout] Reported-by: Russ Anderson <rja@sgi.com> Signed-off-by: Rafael Aquini <aquini@linux.com> Acked-by: Russ Anderson <rja@sgi.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Christoph Lameter <cl@linux.com> Cc: <stable@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/hugetlb.c8
1 files changed, 8 insertions, 0 deletions
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 6402458fee38..bfcf153bc829 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1111,6 +1111,14 @@ static void __init gather_bootmem_prealloc(void)
WARN_ON(page_count(page) != 1);
prep_compound_huge_page(page, h->order);
prep_new_huge_page(h, page, page_to_nid(page));
+ /*
+ * If we had gigantic hugepages allocated at boot time, we need
+ * to restore the 'stolen' pages to totalram_pages in order to
+ * fix confusing memory reports from free(1) and another
+ * side-effects, like CommitLimit going negative.
+ */
+ if (h->order > (MAX_ORDER - 1))
+ totalram_pages += 1 << h->order;
}
}