Re: [patch 1/3 v3] oom: add per-mm oom disable count

[David Rientjes <rientjes@google.com>]

On Mon, 23 Aug 2010, Andrew Morton wrote:

> > --- a/fs/proc/base.c
> > +++ b/fs/proc/base.c
> > @@ -1047,6 +1047,21 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
> >  		return -EACCES;
> >  	}
> >  
> > +	task_lock(task);
> > +	if (!task->mm) {
> > +		task_unlock(task);
> > +		unlock_task_sighand(task, &flags);
> > +		put_task_struct(task);
> > +		return -EINVAL;
> > +	}
> > +
> > +	if (oom_adjust != task->signal->oom_adj) {
> > +		if (oom_adjust == OOM_DISABLE)
> > +			atomic_inc(&task->mm->oom_disable_count);
> > +		if (task->signal->oom_adj == OOM_DISABLE)
> > +			atomic_dec(&task->mm->oom_disable_count);
> > +	}
> 
> scary function.  Wanna try converting oom_adjust_write() to the
> single-exit-with-goto model sometime, see if the result looks more
> maintainable?
> 

Ok, that would certainly be better.

> > --- a/kernel/fork.c
> > +++ b/kernel/fork.c
> > @@ -65,6 +65,7 @@
> >  #include <linux/perf_event.h>
> >  #include <linux/posix-timers.h>
> >  #include <linux/user-return-notifier.h>
> > +#include <linux/oom.h>
> >  
> >  #include <asm/pgtable.h>
> >  #include <asm/pgalloc.h>
> > @@ -485,6 +486,7 @@ static struct mm_struct * mm_init(struct mm_struct * mm, struct task_struct *p)
> >  	mm->cached_hole_size = ~0UL;
> >  	mm_init_aio(mm);
> >  	mm_init_owner(mm, p);
> > +	atomic_set(&mm->oom_disable_count, 0);
> 
> So in fork() we zap this if !CLONE_VM?  Was the CLONE_VM case tested
> nicely?
> 

In clone(), yeah, fork() doesn't use CLONE_VM so the child thread will 
always have a different ->mm.  The new ->mm will get oom_disable_count 
incremented later if tsk has inherited a OOM_DISABLE value.

We've been running with this patch (minus the sys_unshare() code I added) 
for a year now internally.

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