X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=Documentation%2Fsysctl%2Fvm.txt;h=7cee90223d3a0624296b42d983d786b25462dc56;hb=46009c8bcd5d7c9fcbfc17d0455a471bea5be4d4;hp=391dd64363e75b560f68bdd69879946b07cf03da;hpb=1743660b911bfb849b1fb33830522254561b9f9b;p=linux-2.6

diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index 391dd64363..7cee90223d 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -28,6 +28,8 @@ Currently, these files are in /proc/sys/vm:
 - block_dump
 - drop-caches
 - zone_reclaim_mode
+- min_unmapped_ratio
+- panic_on_oom
 
 ==============================================================
 
@@ -126,15 +128,67 @@ the high water marks for each per cpu page list.
 
 zone_reclaim_mode:
 
-This is set during bootup to 1 if it is determined that pages from
-remote zones will cause a significant performance reduction. The
+Zone_reclaim_mode allows to set more or less agressive approaches to
+reclaim memory when a zone runs out of memory. If it is set to zero then no
+zone reclaim occurs. Allocations will be satisfied from other zones / nodes
+in the system.
+
+This is value ORed together of
+
+1	= Zone reclaim on
+2	= Zone reclaim writes dirty pages out
+4	= Zone reclaim swaps pages
+8	= Also do a global slab reclaim pass
+
+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 going off node.
+cache pages that are currently not used) before allocating off node pages.
+
+It may be beneficial to switch off zone reclaim if the system is
+used for a file server and all of memory should be used for caching files
+from disk. In that case the caching effect is more important than
+data locality.
+
+Allowing zone reclaim to write out pages stops processes that are
+writing large amounts of data from dirtying pages on other nodes. Zone
+reclaim will write out dirty pages if a zone fills up and so effectively
+throttle the process. This may decrease the performance of a single process
+since it cannot use all of system memory to buffer the outgoing writes
+anymore but it preserve the memory on other nodes so that the performance
+of other processes running on other nodes will not be affected.
+
+Allowing regular swap effectively restricts allocations to the local
+node unless explicitly overridden by memory policies or cpuset
+configurations.
+
+It may be advisable to allow slab reclaim if the system makes heavy
+use of files and builds up large slab caches. However, the slab
+shrink operation is global, may take a long time and free slabs
+in all nodes of the system.
+
+=============================================================
 
-The user can override this setting. It may be beneficial to switch
-off zone reclaim if the system is used for a file server and all
-of memory should be used for caching files from disk.
+min_unmapped_ratio:
 
-It may be beneficial to switch this on if one wants to do zone
-reclaim regardless of the numa distances in the system.
+This is available only on NUMA kernels.
+
+A percentage of the file backed pages in each zone.  Zone reclaim will only
+occur if more than this percentage of pages are file backed and unmapped.
+This is to insure that a minimal amount of local pages is still available for
+file I/O even if the node is overallocated.
+
+The default is 1 percent.
+
+=============================================================
+
+panic_on_oom
+
+This enables or disables panic on out-of-memory feature.  If this is set to 1,
+the kernel panics when out-of-memory happens.  If this is set to 0, the kernel
+will kill some rogue process, called oom_killer.  Usually, oom_killer can kill
+rogue processes and system will survive.  If you want to panic the system
+rather than killing rogue processes, set this to 1.
+
+The default value is 0.