Messages in this thread |  | | | Date | Thu, 20 Aug 2009 10:46:56 +0530 | | From | Balbir Singh <> | | Subject | Re: [PATCH -v2] mm: do batched scans for mem_cgroup |
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* Wu Fengguang <fengguang.wu@intel.com> [2009-08-20 12:05:33]:
> On Thu, Aug 20, 2009 at 11:13:47AM +0800, KAMEZAWA Hiroyuki wrote: > > On Thu, 20 Aug 2009 10:49:29 +0800 > > Wu Fengguang <fengguang.wu@intel.com> wrote: > > > > > For mem_cgroup, shrink_zone() may call shrink_list() with nr_to_scan=1, > > > in which case shrink_list() _still_ calls isolate_pages() with the much > > > larger SWAP_CLUSTER_MAX. It effectively scales up the inactive list > > > scan rate by up to 32 times. > > > > > > For example, with 16k inactive pages and DEF_PRIORITY=12, (16k >> 12)=4. > > > So when shrink_zone() expects to scan 4 pages in the active/inactive > > > list, it will be scanned SWAP_CLUSTER_MAX=32 pages in effect. > > > > > > The accesses to nr_saved_scan are not lock protected and so not 100% > > > accurate, however we can tolerate small errors and the resulted small > > > imbalanced scan rates between zones. > > > > > > This batching won't blur up the cgroup limits, since it is driven by > > > "pages reclaimed" rather than "pages scanned". When shrink_zone() > > > decides to cancel (and save) one smallish scan, it may well be called > > > again to accumulate up nr_saved_scan. > > > > > > It could possibly be a problem for some tiny mem_cgroup (which may be > > > _full_ scanned too much times in order to accumulate up nr_saved_scan). > > > > > > CC: Rik van Riel <riel@redhat.com> > > > CC: Minchan Kim <minchan.kim@gmail.com> > > > CC: Balbir Singh <balbir@linux.vnet.ibm.com> > > > CC: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> > > > CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> > > > Signed-off-by: Wu Fengguang <fengguang.wu@intel.com> > > > --- > > > > Hmm, how about this ? > > == > > Now, nr_saved_scan is tied to zone's LRU. > > But, considering how vmscan works, it should be tied to reclaim_stat. > > > > By this, memcg can make use of nr_saved_scan information seamlessly. > > Good idea, full patch updated with your signed-off-by :) > > Thanks, > Fengguang > --- > mm: do batched scans for mem_cgroup > > For mem_cgroup, shrink_zone() may call shrink_list() with nr_to_scan=1, > in which case shrink_list() _still_ calls isolate_pages() with the much > larger SWAP_CLUSTER_MAX. It effectively scales up the inactive list > scan rate by up to 32 times. > > For example, with 16k inactive pages and DEF_PRIORITY=12, (16k >> 12)=4. > So when shrink_zone() expects to scan 4 pages in the active/inactive > list, it will be scanned SWAP_CLUSTER_MAX=32 pages in effect. > > The accesses to nr_saved_scan are not lock protected and so not 100% > accurate, however we can tolerate small errors and the resulted small > imbalanced scan rates between zones. > > This batching won't blur up the cgroup limits, since it is driven by > "pages reclaimed" rather than "pages scanned". When shrink_zone() > decides to cancel (and save) one smallish scan, it may well be called > again to accumulate up nr_saved_scan. > > It could possibly be a problem for some tiny mem_cgroup (which may be > _full_ scanned too much times in order to accumulate up nr_saved_scan). >
Looks good to me, how did you test it?
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
-- Balbir
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