On Tue, Nov 09, 2010 at 10:11:45PM +0100, Andrea Arcangeli wrote: > On Tue, Nov 09, 2010 at 03:20:33PM +0900, KOSAKI Motohiro wrote: > > > From: Andrea Arcangeli <aarcange@xxxxxxxxxx> > > > > > > With transparent hugepage support we need compaction for the "defrag" sysfs > > > controls to be effective. > > > > > > Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx> > > > --- > > > > > > diff --git a/mm/Kconfig b/mm/Kconfig > > > --- a/mm/Kconfig > > > +++ b/mm/Kconfig > > > @@ -305,6 +305,7 @@ config NOMMU_INITIAL_TRIM_EXCESS > > > config TRANSPARENT_HUGEPAGE > > > bool "Transparent Hugepage Support" > > > depends on X86 && MMU > > > + select COMPACTION > > > help > > > Transparent Hugepages allows the kernel to use huge pages and > > > huge tlb transparently to the applications whenever possible. > > > > I dislike this. THP and compaction are completely orthogonal. I think > > you are talking only your performance recommendation. I mean I dislike > > Kconfig 'select' hell and I hope every developers try to avoid it as > > far as possible. > > At the moment THP hangs the system if COMPACTION isn't selected Just to confirm - by hang, you mean grinds to a slow pace as opposed to coming to a complete stop and having to restart? If so then Acked-by: Mel Gorman <mel@xxxxxxxxx> > (please try yourself if you don't believe), as without COMPACTION > lumpy reclaim wouldn't be entirely disabled. So at the moment it's not > orthogonal. When lumpy will be removed from the VM (like I tried > multiple times to achieve) I can remove the select COMPACTION in > theory, but then 99% of THP users would be still doing a mistake in > disabling compaction, even if the mistake won't return in fatal > runtime but just slightly degraded performance. > -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>