Re: [PATCH] vmscan: check all_unreclaimable in direct reclaim path

[Johannes Weiner]

On Sun, Sep 05, 2010 at 11:40:37PM +0900, Minchan Kim wrote:
> M. Vefa Bicakci reported 2.6.35 kernel hang up when hibernation on his
> 32bit 3GB mem machine. (https://bugzilla.kernel.org/show_bug.cgi?id=16771)
> Also he was bisected first bad commit is below
> 
>   commit bb21c7ce18eff8e6e7877ca1d06c6db719376e3c
>   Author: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
>   Date:   Fri Jun 4 14:15:05 2010 -0700
> 
>      vmscan: fix do_try_to_free_pages() return value when priority==0 reclaim failure
> 
> At first impression, this seemed very strange because the above commit only
> chenged function return value and hibernate_preallocate_memory() ignore
> return value of shrink_all_memory(). But it's related.
> 
> Now, page allocation from hibernation code may enter infinite loop if
> the system has highmem. The reasons are that vmscan don't care enough 
> OOM case when oom_killer_disabled. 
> 
> The problem sequence is following as. 
> 
> 1. hibernation
> 2. oom_disable
> 3. alloc_pages
> 4. do_try_to_free_pages
>        if (scanning_global_lru(sc) && !all_unreclaimable)
>                return 1;
> 
> If kswapd is not freezed, it would set zone->all_unreclaimable to 1 and then
> shrink_zones maybe return true(ie, all_unreclaimable is true). 
> so at last, alloc_pages could go to _nopage_. If it is, it should have no problem.
> 
> This patch adds all_unreclaimable check to protect in direct reclaim path, too.
> It can care of hibernation OOM case and help bailout all_unreclaimable case slightly.
> 
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: "Rafael J. Wysocki" <rjw@xxxxxxx>
> Cc: M. Vefa Bicakci <bicave@xxxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxx
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx>
> ---
>  mm/vmscan.c |   33 +++++++++++++++++++++++++++------
>  1 files changed, 27 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index f620ab3..53b23a7 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1893,12 +1893,11 @@ static void shrink_zone(int priority, struct zone *zone,
>   * If a zone is deemed to be full of pinned pages then just give it a light
>   * scan then give up on it.
>   */
> -static bool shrink_zones(int priority, struct zonelist *zonelist,
> +static void shrink_zones(int priority, struct zonelist *zonelist,
>  					struct scan_control *sc)
>  {
>  	struct zoneref *z;
>  	struct zone *zone;
> -	bool all_unreclaimable = true;
>  
>  	for_each_zone_zonelist_nodemask(zone, z, zonelist,
>  					gfp_zone(sc->gfp_mask), sc->nodemask) {
> @@ -1916,8 +1915,31 @@ static bool shrink_zones(int priority, struct zonelist *zonelist,
>  		}
>  
>  		shrink_zone(priority, zone, sc);
> -		all_unreclaimable = false;
>  	}
> +}
> +
> +static inline bool all_unreclaimable(struct zonelist *zonelist,
> +		struct scan_control *sc)
> +{
> +	struct zoneref *z;
> +	struct zone *zone;
> +	bool all_unreclaimable = true;
> +
> +	if (!scanning_global_lru(sc))
> +		return false;
> +
> +	for_each_zone_zonelist_nodemask(zone, z, zonelist,
> +			gfp_zone(sc->gfp_mask), sc->nodemask) {
> +		if (!populated_zone(zone))
> +			continue;
> +		if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
> +			continue;
> +		if (zone->pages_scanned < (zone_reclaimable_pages(zone) * 6)) {

Small nitpick: kswapd does the same check against the magic number,
could you move it into a separate function?  zone_reclaimable()?

Otherwise,
Reviewed-by: Johannes Weiner <hannes@xxxxxxxxxxx>

> +			all_unreclaimable = false;
> +			break;
> +		}
> +	}
> +
>  	return all_unreclaimable;
>  }
>  
> @@ -1941,7 +1963,6 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
>  					struct scan_control *sc)
>  {
>  	int priority;
> -	bool all_unreclaimable;
>  	unsigned long total_scanned = 0;
>  	struct reclaim_state *reclaim_state = current->reclaim_state;
>  	struct zoneref *z;
> @@ -1958,7 +1979,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
>  		sc->nr_scanned = 0;
>  		if (!priority)
>  			disable_swap_token();
> -		all_unreclaimable = shrink_zones(priority, zonelist, sc);
> +		shrink_zones(priority, zonelist, sc);
>  		/*
>  		 * Don't shrink slabs when reclaiming memory from
>  		 * over limit cgroups
> @@ -2020,7 +2041,7 @@ out:
>  		return sc->nr_reclaimed;
>  
>  	/* top priority shrink_zones still had more to do? don't OOM, then */
> -	if (scanning_global_lru(sc) && !all_unreclaimable)
> +	if (!all_unreclaimable(zonelist, sc))
>  		return 1;
>  
>  	return 0;
> -- 
> 1.7.0.5
> 
> 
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