Re: [patch v2 1/2] oom: avoid killing a task if a thread sharing its mm cannot be killed

[David Rientjes <rientjes@google.com>]

On Wed, 18 Aug 2010, KAMEZAWA Hiroyuki wrote:

> > The oom killer's goal is to kill a memory-hogging task so that it may
> > exit, free its memory, and allow the current context to allocate the
> > memory that triggered it in the first place.  Thus, killing a task is
> > pointless if other threads sharing its mm cannot be killed because of its
> > /proc/pid/oom_adj or /proc/pid/oom_score_adj value.
> > 
> > This patch checks all user threads on the system to determine whether
> > oom_badness(p) should return 0 for p, which means it should not be killed.
> > If a thread shares p's mm and is unkillable, p is considered to be
> > unkillable as well.
> > 
> > Kthreads are not considered toward this rule since they only temporarily
> > assume a task's mm via use_mm().
> > 
> > Signed-off-by: David Rientjes <rientjes@google.com>
> 
> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> 

Thanks!

> Thank you. BTW, do you have good idea for speed-up ?
> This code seems terribly slow when a system has many processes.
> 

I was thinking about adding an "unsinged long oom_kill_disable_count" to 
struct mm_struct that would atomically increment anytime a task attached 
to it had a signal->oom_score_adj of OOM_SCORE_ADJ_MIN.

The proc handler when changing /proc/pid/oom_score_adj would inc or dec 
the counter depending on the new value, and exit_mm() would dec the 
counter if current->signal->oom_score_adj is OOM_SCORE_ADJ_MIN.

What do you think?

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