Subject: disable transparent hugepages by default on small systems From: Rik van Riel On small systems, the extra memory used by the anti-fragmentation memory reserve and simply because huge pages are smaller than large pages can easily outweigh the benefits of less TLB misses. A less obvious concern is if run on a NUMA machine with asymmetric node sizes and one of them is very small. The reserve could make the node unusable. In case of the crashdump kernel, OOMs have been observed due to the anti-fragmentation memory reserve taking up a large fraction of the crashdump image. This patch disables transparent hugepages on systems with less than 1GB of RAM, but the hugepage subsystem is fully initialized so administrators can enable THP through /sys if desired. v2: reduce the limit to 512MB Signed-off-by: Rik van Riel Acked-by: Avi Kiviti Signed-off-by: Andrea Arcangeli Acked-by: Mel Gorman --- diff --git a/mm/huge_memory.c b/mm/huge_memory.c --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -527,6 +527,14 @@ static int __init hugepage_init(void) goto out; } + /* + * By default disable transparent hugepages on smaller systems, + * where the extra memory used could hurt more than TLB overhead + * is likely to save. The admin can still enable it through /sys. + */ + if (totalram_pages < (512 << (20 - PAGE_SHIFT))) + transparent_hugepage_flags = 0; + start_khugepaged(); set_recommended_min_free_kbytes();