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    Subject[PATCH 3.8 106/124] mm, oom: base root bonus on current usage
    Date
    3.8.13.18 -stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: David Rientjes <rientjes@google.com>

    commit 778c14affaf94a9e4953179d3e13a544ccce7707 upstream.

    A 3% of system memory bonus is sometimes too excessive in comparison to
    other processes.

    With commit a63d83f427fb ("oom: badness heuristic rewrite"), the OOM
    killer tries to avoid killing privileged tasks by subtracting 3% of
    overall memory (system or cgroup) from their per-task consumption. But
    as a result, all root tasks that consume less than 3% of overall memory
    are considered equal, and so it only takes 33+ privileged tasks pushing
    the system out of memory for the OOM killer to do something stupid and
    kill dhclient or other root-owned processes. For example, on a 32G
    machine it can't tell the difference between the 1M agetty and the 10G
    fork bomb member.

    The changelog describes this 3% boost as the equivalent to the global
    overcommit limit being 3% higher for privileged tasks, but this is not
    the same as discounting 3% of overall memory from _every privileged task
    individually_ during OOM selection.

    Replace the 3% of system memory bonus with a 3% of current memory usage
    bonus.

    By giving root tasks a bonus that is proportional to their actual size,
    they remain comparable even when relatively small. In the example
    above, the OOM killer will discount the 1M agetty's 256 badness points
    down to 179, and the 10G fork bomb's 262144 points down to 183500 points
    and make the right choice, instead of discounting both to 0 and killing
    agetty because it's first in the task list.

    Signed-off-by: David Rientjes <rientjes@google.com>
    Reported-by: Johannes Weiner <hannes@cmpxchg.org>
    Acked-by: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Michal Hocko <mhocko@suse.cz>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    Documentation/filesystems/proc.txt | 4 ++--
    mm/oom_kill.c | 2 +-
    2 files changed, 3 insertions(+), 3 deletions(-)

    diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
    index fd8d0d5..954eab8 100644
    --- a/Documentation/filesystems/proc.txt
    +++ b/Documentation/filesystems/proc.txt
    @@ -1372,8 +1372,8 @@ 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.
    +There is an additional factor included in the badness score: the current memory
    +and swap usage is discounted by 3% for root processes.

    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
    diff --git a/mm/oom_kill.c b/mm/oom_kill.c
    index 0399f14..4eac855 100644
    --- a/mm/oom_kill.c
    +++ b/mm/oom_kill.c
    @@ -170,7 +170,7 @@ unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
    * implementation used by LSMs.
    */
    if (has_capability_noaudit(p, CAP_SYS_ADMIN))
    - adj -= 30;
    + points -= (points * 3) / 100;

    /* Normalize to oom_score_adj units */
    adj *= totalpages / 1000;
    --
    1.8.3.2


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