Re: [patch 1/2] arch: invoke oom-killer from page fault

[Michal Hocko]

On Thu 06-06-13 00:36:20, Johannes Weiner wrote:
> On Wed, Jun 05, 2013 at 08:57:44PM -0700, David Rientjes wrote:
> > On Wed, 5 Jun 2013, Johannes Weiner wrote:
> > 
> > > Since '1c0fe6e mm: invoke oom-killer from page fault', page fault
> > > handlers should not directly kill faulting tasks in an out of memory
> > > condition.
> > 
> > I have no objection to the patch, but there's no explanation given here 
> > why exiting with a kill shouldn't be done.  Is it because of memory 
> > reserves and there is no guarantee that current will be able to exit?  Or 
> > is it just for consistency with other archs?
> > 
> > > Instead, they should be invoking the OOM killer to pick
> > > the right task.  Convert the remaining architectures.
> > > 
> > 
> > If this is a matter of memory reserves, I guess you could point people who 
> > want the current behavior (avoiding the expensiveness of the tasklist scan 
> > in the oom killer for example) to /proc/sys/vm/oom_kill_allocating_task?
> > 
> > This changelog is a bit cryptic in its motivation.
> 
> Fixing copy-pasted bitrot^W^W^W^WHow about this?
> 
> ---
> From: Johannes Weiner <hannes@xxxxxxxxxxx>
> Subject: [patch] mm: invoke oom-killer from remaining unconverted page fault
>  handlers
> 
> A few remaining architectures directly kill the page faulting task in
> an out of memory situation.  This is usually not a good idea since
> that task might not even use a significant amount of memory and so may
> not be the optimal victim to resolve the situation.
> 
> Since '1c0fe6e mm: invoke oom-killer from page fault' (2.6.29) there
> is a hook that architecture page fault handlers are supposed to call
> to invoke the OOM killer and let it pick the right task to kill.
> Convert the remaining architectures over to this hook.
> 
> To have the previous behavior of simply taking out the faulting task
> the vm.oom_kill_allocating_task sysctl can be set to 1.
> 
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>

It was much easier than I thought.
Reviewed-by: Michal Hocko <mhocko@xxxxxxx>

> ---
>  arch/arc/mm/fault.c      | 6 ++++--
>  arch/metag/mm/fault.c    | 6 ++++--
>  arch/mn10300/mm/fault.c  | 7 ++++---
>  arch/openrisc/mm/fault.c | 8 ++++----
>  arch/score/mm/fault.c    | 8 ++++----
>  arch/tile/mm/fault.c     | 8 ++++----
>  6 files changed, 24 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c
> index c0decc1..d5ec60a 100644
> --- a/arch/arc/mm/fault.c
> +++ b/arch/arc/mm/fault.c
> @@ -207,8 +207,10 @@ out_of_memory:
>  	}
>  	up_read(&mm->mmap_sem);
>  
> -	if (user_mode(regs))
> -		do_group_exit(SIGKILL);	/* This will never return */
> +	if (user_mode(regs)) {
> +		pagefault_out_of_memory();
> +		return;
> +	}
>  
>  	goto no_context;
>  
> diff --git a/arch/metag/mm/fault.c b/arch/metag/mm/fault.c
> index 2c75bf7..8fddf46 100644
> --- a/arch/metag/mm/fault.c
> +++ b/arch/metag/mm/fault.c
> @@ -224,8 +224,10 @@ do_sigbus:
>  	 */
>  out_of_memory:
>  	up_read(&mm->mmap_sem);
> -	if (user_mode(regs))
> -		do_group_exit(SIGKILL);
> +	if (user_mode(regs)) {
> +		pagefault_out_of_memory();
> +		return 1;
> +	}
>  
>  no_context:
>  	/* Are we prepared to handle this kernel fault?  */
> diff --git a/arch/mn10300/mm/fault.c b/arch/mn10300/mm/fault.c
> index d48a84f..8a2e6de 100644
> --- a/arch/mn10300/mm/fault.c
> +++ b/arch/mn10300/mm/fault.c
> @@ -345,9 +345,10 @@ no_context:
>   */
>  out_of_memory:
>  	up_read(&mm->mmap_sem);
> -	printk(KERN_ALERT "VM: killing process %s\n", tsk->comm);
> -	if ((fault_code & MMUFCR_xFC_ACCESS) == MMUFCR_xFC_ACCESS_USR)
> -		do_exit(SIGKILL);
> +	if ((fault_code & MMUFCR_xFC_ACCESS) == MMUFCR_xFC_ACCESS_USR) {
> +		pagefault_out_of_memory();
> +		return;
> +	}
>  	goto no_context;
>  
>  do_sigbus:
> diff --git a/arch/openrisc/mm/fault.c b/arch/openrisc/mm/fault.c
> index e2bfafc..4a41f84 100644
> --- a/arch/openrisc/mm/fault.c
> +++ b/arch/openrisc/mm/fault.c
> @@ -267,10 +267,10 @@ out_of_memory:
>  	__asm__ __volatile__("l.nop 1");
>  
>  	up_read(&mm->mmap_sem);
> -	printk("VM: killing process %s\n", tsk->comm);
> -	if (user_mode(regs))
> -		do_exit(SIGKILL);
> -	goto no_context;
> +	if (!user_mode(regs))
> +		goto no_context;
> +	pagefault_out_of_memory();
> +	return;
>  
>  do_sigbus:
>  	up_read(&mm->mmap_sem);
> diff --git a/arch/score/mm/fault.c b/arch/score/mm/fault.c
> index 47b600e..6b18fb0 100644
> --- a/arch/score/mm/fault.c
> +++ b/arch/score/mm/fault.c
> @@ -172,10 +172,10 @@ out_of_memory:
>  		down_read(&mm->mmap_sem);
>  		goto survive;
>  	}
> -	printk("VM: killing process %s\n", tsk->comm);
> -	if (user_mode(regs))
> -		do_group_exit(SIGKILL);
> -	goto no_context;
> +	if (!user_mode(regs))
> +		goto no_context;
> +	pagefault_out_of_memory();
> +	return;
>  
>  do_sigbus:
>  	up_read(&mm->mmap_sem);
> diff --git a/arch/tile/mm/fault.c b/arch/tile/mm/fault.c
> index 3d2b81c..f7f99f9 100644
> --- a/arch/tile/mm/fault.c
> +++ b/arch/tile/mm/fault.c
> @@ -573,10 +573,10 @@ out_of_memory:
>  		down_read(&mm->mmap_sem);
>  		goto survive;
>  	}
> -	pr_alert("VM: killing process %s\n", tsk->comm);
> -	if (!is_kernel_mode)
> -		do_group_exit(SIGKILL);
> -	goto no_context;
> +	if (is_kernel_mode)
> +		goto no_context;
> +	pagefault_out_of_memory();
> +	return 0;
>  
>  do_sigbus:
>  	up_read(&mm->mmap_sem);
> -- 
> 1.8.2.3
> 

-- 
Michal Hocko
SUSE Labs
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