[PATCH 3/3] sysctl/vm.txt: Update document

[Kemi Wang <kemi.wang@intel.com>]

Add a paragraph to introduce the functionality and usage on vmstat_mode in
sysctl/vm.txt

Reported-by: Jesper Dangaard Brouer <brouer@redhat.com>
Suggested-by: Dave Hansen <dave.hansen@intel.com>
Suggested-by: Ying Huang <ying.huang@intel.com>
Signed-off-by: Kemi Wang <kemi.wang@intel.com>
---
 Documentation/sysctl/vm.txt | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index 9baf66a..6ab2843 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -61,6 +61,7 @@ Currently, these files are in /proc/sys/vm:
 - swappiness
 - user_reserve_kbytes
 - vfs_cache_pressure
+- vmstat_mode
 - watermark_scale_factor
 - zone_reclaim_mode
 
@@ -843,6 +844,31 @@ ten times more freeable objects than there are.
 
 =============================================================
 
+vmstat_mode
+
+This interface allows virtual memory statistics configurable.
+
+When performance becomes a bottleneck and you can tolerate some possible
+tool breakage and some decreased counter precision (e.g. numa counter), you
+can do:
+	echo [C|c]oarse > /proc/sys/vm/vmstat_mode
+ignorable statistics list:
+- numa counters
+
+When performance is not a bottleneck and you want all tooling to work, you
+can do:
+	echo [S|s]trict > /proc/sys/vm/vmstat_mode
+
+We recommend automatic detection of virtual memory statistics by system,
+this is also system default configuration, you can do:
+	echo [A|a]uto > /proc/sys/vm/vmstat_mode
+
+E.g. numa statistics does not affect system's decision and it is very
+rarely consumed. If set vmstat_mode = auto, numa counters update is skipped
+unless the counter is *read* by users at least once.
+
+==============================================================
+
 watermark_scale_factor:
 
 This factor controls the aggressiveness of kswapd. It defines the
-- 
2.7.4

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