Commit 97562cd2 authored Jan 13, 2011 by Rik van Riel Committed by Linus Torvalds Jan 13, 2011

thp: disable transparent hugepages by default on small systems



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.

Signed-off-by: Rik van Riel <riel@redhat.com>
Acked-by: Avi Kiviti <avi@redhat.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent c5a73c3d

mm/huge_memory.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -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();

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