On Thu, Sep 01, 2011 at 12:14:58PM +0800, Wu Fengguang wrote: > Hi Stefan, > > On Wed, Aug 31, 2011 at 03:11:02PM +0800, Stefan Priebe - Profihost AG wrote: > > Hi Fengguang, > > Hi Yanhai, > > > > > you're abssolutely corect zone_reclaim_mode is on - but why? > > > There must be some linux software which switches it on. > > > > > > ~# grep 'zone_reclaim_mode' /etc/sysctl.* -r -i > > > ~# > > > > > > also > > > ~# grep 'zone_reclaim_mode' /etc/sysctl.* -r -i > > > ~# > > > > > > tells us nothing. > > > > > > I've then read this: > > > > > > "zone_reclaim_mode is set during bootup to 1 if it is determined that > > > pages from remote zones will cause a measurable performance reduction. > > > The page allocator will then reclaim easily reusable pages (those page > > > cache pages that are currently not used) before allocating off node pages." > > > > > > Why does the kernel do that here in our case on these machines. > > > > Can nobody help why the kernel in this case set it to 1? > > It's determined by RECLAIM_DISTANCE. > > build_zonelists(): > > /* > * If another node is sufficiently far away then it is better > * to reclaim pages in a zone before going off node. > */ > if (distance > RECLAIM_DISTANCE) > zone_reclaim_mode = 1; > > Since Linux v3.0 RECLAIM_DISTANCE is increased from 20 to 30 by this commit. > It may well help your case, too. > Even with that, it's known that zone_reclaim() can be a disaster when it runs into problems. This should be fixed in 3.1 by the following commits; [cd38b115 mm: page allocator: initialise ZLC for first zone eligible for zone_reclaim] [76d3fbf8 mm: page allocator: reconsider zones for allocation after direct reclaim] The description in cd38b115 has the interesting details. -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>