Messages in this thread Patch in this message | | | Date | Sun, 16 Aug 2009 13:41:07 +0800 | From | Wu Fengguang <> | Subject | Re: [RFC] respect the referenced bit of KVM guest pages? |
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On Sun, Aug 16, 2009 at 01:09:03PM +0800, Balbir Singh wrote: > * Wu Fengguang <fengguang.wu@intel.com> [2009-08-15 13:45:24]: > > > On Fri, Aug 14, 2009 at 09:19:35PM +0800, Rik van Riel wrote: > > > Wu Fengguang wrote: > > > > On Fri, Aug 14, 2009 at 05:10:55PM +0800, Johannes Weiner wrote: > > > > > > >> So even with the active list being a FIFO, we keep usage information > > > >> gathered from the inactive list. If we deactivate pages in arbitrary > > > >> list intervals, we throw this away. > > > > > > > > We do have the danger of FIFO, if inactive list is small enough, so > > > > that (unconditionally) deactivated pages quickly get reclaimed and > > > > their life window in inactive list is too small to be useful. > > > > > > This one of the reasons why we unconditionally deactivate > > > the active anon pages, and do background scanning of the > > > active anon list when reclaiming page cache pages. > > > > > > We want to always move some pages to the inactive anon > > > list, so it does not get too small. > > > > Right, the current code tries to pull inactive list out of > > smallish-size state as long as there are vmscan activities. > > > > However there is a possible (and tricky) hole: mem cgroups > > don't do batched vmscan. 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 10 times when > > it is still small, and may thus prevent it from growing up for ever. > > > > I think we need to possibly export some scanning data under DEBUG_VM > to cross verify.
Maybe we can do more general debugging code, but here is a quick patch for examining the cgroup case. Note that even for the global zones, max_scan may well not be the multiple of SWAP_CLUSTER_MAX, thus shrink_inactive_list() will scan a little more in its last loop.
--- mm/vmscan.c | 7 +++++++ 1 file changed, 7 insertions(+)
--- linux.orig/mm/vmscan.c 2009-08-16 13:24:25.000000000 +0800 +++ linux/mm/vmscan.c 2009-08-16 13:38:32.000000000 +0800 @@ -1043,6 +1043,13 @@ static unsigned long shrink_inactive_lis struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc); int lumpy_reclaim = 0; + if (!scanning_global_lru(sc)) + printk("shrink inactive %s count=%lu scan=%lu\n", + file ? "file" : "anon", + mem_cgroup_zone_nr_pages(sc->mem_cgroup, zone, + LRU_INACTIVE_ANON + !!file), + max_scan); + /* * If we need a large contiguous chunk of memory, or have * trouble getting a small set of contiguous pages, we
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