2.6.39-stable review patch. If anyone has any objections, please let us know.
------------------ From: Rafael Aquini <[email protected]> commit b0320c7b7d1ac1bd5c2d9dff3258524ab39bad32 upstream. 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). [[email protected]: standardize comment layout] Reported-by: Russ Anderson <[email protected]> Signed-off-by: Rafael Aquini <[email protected]> Acked-by: Russ Anderson <[email protected]> Cc: Andrea Arcangeli <[email protected]> Cc: Christoph Lameter <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- mm/hugetlb.c | 8 ++++++++ 1 file changed, 8 insertions(+) --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -1111,6 +1111,14 @@ static void __init gather_bootmem_preall 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; } } _______________________________________________ stable mailing list [email protected] http://linux.kernel.org/mailman/listinfo/stable
