1 files changed, 57 insertions, 37 deletions

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 8fe8895894d8..cf1295c2bb66 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -33,7 +33,8 @@ Table of Contents
   2     Modifying System Parameters
 
   3     Per-Process Parameters
-  3.1   /proc/<pid>/oom_adj - Adjust the oom-killer score
+  3.1   /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj - Adjust the oom-killer
+                                                                score
   3.2   /proc/<pid>/oom_score - Display current oom-killer score
   3.3   /proc/<pid>/io - Display the IO accounting fields
   3.4   /proc/<pid>/coredump_filter - Core dump filtering settings
@@ -1234,42 +1235,61 @@ of the kernel.
 CHAPTER 3: PER-PROCESS PARAMETERS
 ------------------------------------------------------------------------------
 
-3.1 /proc/<pid>/oom_adj - Adjust the oom-killer score
-------------------------------------------------------
-
-This file can be used to adjust the score used to select which processes
-should be killed in an  out-of-memory  situation.  Giving it a high score will
-increase the likelihood of this process being killed by the oom-killer.  Valid
-values are in the range -16 to +15, plus the special value -17, which disables
-oom-killing altogether for this process.
-
-The process to be killed in an out-of-memory situation is selected among all others
-based on its badness score. This value equals the original memory size of the process
-and is then updated according to its CPU time (utime + stime) and the
-run time (uptime - start time). The longer it runs the smaller is the score.
-Badness score is divided by the square root of the CPU time and then by
-the double square root of the run time.
-
-Swapped out tasks are killed first. Half of each child's memory size is added to
-the parent's score if they do not share the same memory. Thus forking servers
-are the prime candidates to be killed. Having only one 'hungry' child will make
-parent less preferable than the child.
-
-/proc/<pid>/oom_score shows process' current badness score.
-
-The following heuristics are then applied:
- * if the task was reniced, its score doubles
- * superuser or direct hardware access tasks (CAP_SYS_ADMIN, CAP_SYS_RESOURCE
-        or CAP_SYS_RAWIO) have their score divided by 4
- * if oom condition happened in one cpuset and checked process does not belong
-        to it, its score is divided by 8
- * the resulting score is multiplied by two to the power of oom_adj, i.e.
-        points <<= oom_adj when it is positive and
-        points >>= -(oom_adj) otherwise
-
-The task with the highest badness score is then selected and its children
-are killed, process itself will be killed in an OOM situation when it does
-not have children or some of them disabled oom like described above.
+3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
+--------------------------------------------------------------------------------
+
+These file can be used to adjust the badness heuristic used to select which
+process gets killed in out of memory conditions.
+
+The badness heuristic assigns a value to each candidate task ranging from 0
+(never kill) to 1000 (always kill) to determine which process is targeted.  The
+units are roughly a proportion along that range of allowed memory the process
+may allocate from based on an estimation of its current memory and swap use.
+For example, if a task is using all allowed memory, its badness score will be
+1000.  If it is using half of its allowed memory, its score will be 500.
+
+There is an additional factor included in the badness score: root
+processes are given 3% extra memory over other tasks.
+
+The amount of "allowed" memory depends on the context in which the oom killer
+was called.  If it is due to the memory assigned to the allocating task's cpuset
+being exhausted, the allowed memory represents the set of mems assigned to that
+cpuset.  If it is due to a mempolicy's node(s) being exhausted, the allowed
+memory represents the set of mempolicy nodes.  If it is due to a memory
+limit (or swap limit) being reached, the allowed memory is that configured
+limit.  Finally, if it is due to the entire system being out of memory, the
+allowed memory represents all allocatable resources.
+
+The value of /proc/<pid>/oom_score_adj is added to the badness score before it
+is used to determine which task to kill.  Acceptable values range from -1000
+(OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX).  This allows userspace to
+polarize the preference for oom killing either by always preferring a certain
+task or completely disabling it.  The lowest possible value, -1000, is
+equivalent to disabling oom killing entirely for that task since it will always
+report a badness score of 0.
+
+Consequently, it is very simple for userspace to define the amount of memory to
+consider for each task.  Setting a /proc/<pid>/oom_score_adj value of +500, for
+example, is roughly equivalent to allowing the remainder of tasks sharing the
+same system, cpuset, mempolicy, or memory controller resources to use at least
+50% more memory.  A value of -500, on the other hand, would be roughly
+equivalent to discounting 50% of the task's allowed memory from being considered
+as scoring against the task.
+
+For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
+be used to tune the badness score.  Its acceptable values range from -16
+(OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
+(OOM_DISABLE) to disable oom killing entirely for that task.  Its value is
+scaled linearly with /proc/<pid>/oom_score_adj.
+
+Writing to /proc/<pid>/oom_score_adj or /proc/<pid>/oom_adj will change the
+other with its scaled value.
+
+Caveat: when a parent task is selected, the oom killer will sacrifice any first
+generation children with seperate address spaces instead, if possible.  This
+avoids servers and important system daemons from being killed and loses the
+minimal amount of work.
+
 
 3.2 /proc/<pid>/oom_score - Display current oom-killer score
 -------------------------------------------------------------