Re: [patch 2/4] mm, oom: cleanup pagefault oom handler

[Michal Hocko <mhocko@suse.cz>]

On Wed 14-11-12 01:15:22, David Rientjes wrote:
> To lock the entire system from parallel oom killing, it's possible to
> pass in a zonelist with all zones rather than using
> for_each_populated_zone() for the iteration.  This obsoletes
> try_set_system_oom() and clear_system_oom() so that they can be removed.
> 
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> Cc: Michal Hocko <mhocko@suse.cz>
> Signed-off-by: David Rientjes <rientjes@google.com>

The only _potential_ problem I can see with this is that if we ever have
a HW which requires that a node zonelist doesn't contain others nodes'
zones then this wouldn't work. I do not think such a HW exists. Such a HW
would need more changes in the code anyway.

so
Reviewed-by: Michal Hocko <mhocko@suse.cz>

> ---
>  mm/oom_kill.c |   49 +++++++------------------------------------------
>  1 files changed, 7 insertions(+), 42 deletions(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -591,43 +591,6 @@ void clear_zonelist_oom(struct zonelist *zonelist, gfp_t gfp_mask)
>  	spin_unlock(&zone_scan_lock);
>  }
>  
> -/*
> - * Try to acquire the oom killer lock for all system zones.  Returns zero if a
> - * parallel oom killing is taking place, otherwise locks all zones and returns
> - * non-zero.
> - */
> -static int try_set_system_oom(void)
> -{
> -	struct zone *zone;
> -	int ret = 1;
> -
> -	spin_lock(&zone_scan_lock);
> -	for_each_populated_zone(zone)
> -		if (zone_is_oom_locked(zone)) {
> -			ret = 0;
> -			goto out;
> -		}
> -	for_each_populated_zone(zone)
> -		zone_set_flag(zone, ZONE_OOM_LOCKED);
> -out:
> -	spin_unlock(&zone_scan_lock);
> -	return ret;
> -}
> -
> -/*
> - * Clears ZONE_OOM_LOCKED for all system zones so that failed allocation
> - * attempts or page faults may now recall the oom killer, if necessary.
> - */
> -static void clear_system_oom(void)
> -{
> -	struct zone *zone;
> -
> -	spin_lock(&zone_scan_lock);
> -	for_each_populated_zone(zone)
> -		zone_clear_flag(zone, ZONE_OOM_LOCKED);
> -	spin_unlock(&zone_scan_lock);
> -}
> -
>  /**
>   * out_of_memory - kill the "best" process when we run out of memory
>   * @zonelist: zonelist pointer
> @@ -708,15 +671,17 @@ out:
>  
>  /*
>   * The pagefault handler calls here because it is out of memory, so kill a
> - * memory-hogging task.  If a populated zone has ZONE_OOM_LOCKED set, a parallel
> - * oom killing is already in progress so do nothing.  If a task is found with
> - * TIF_MEMDIE set, it has been killed so do nothing and allow it to exit.
> + * memory-hogging task.  If any populated zone has ZONE_OOM_LOCKED set, a
> + * parallel oom killing is already in progress so do nothing.
>   */
>  void pagefault_out_of_memory(void)
>  {
> -	if (try_set_system_oom()) {
> +	struct zonelist *zonelist = node_zonelist(first_online_node,
> +						  GFP_KERNEL);
> +
> +	if (try_set_zonelist_oom(zonelist, GFP_KERNEL)) {
>  		out_of_memory(NULL, 0, 0, NULL, false);
> -		clear_system_oom();
> +		clear_zonelist_oom(zonelist, GFP_KERNEL);
>  	}
>  	schedule_timeout_killable(1);
>  }

-- 
Michal Hocko
SUSE Labs