Re: [PATCH v2] vmscan: check all_unreclaimable in direct reclaim path

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Sunday, September 12, 2010, Minchan Kim wrote:
> Adnrew, Please drop my old version and merge this verstion.
> (old : vmscan-check-all_unreclaimable-in-direct-reclaim-path.patch)
>    
>  * Changelog from v2 
>    * remove inline - suggested by Andrew
>    * add function desription - suggeseted by Adnrew
> 
> == CUT HERE == 

For the record, this commit:

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=6715045ddc7472a22be5e49d4047d2d89b391f45

is reported to fix the problem without the $subject patch (see
http://lkml.org/lkml/2010/9/11/129).  So, I'm not sure if it's still necessary
to special case this particular situation?

Thanks,
Rafael


> Subject: [PATCH v2] vmscan: check all_unreclaimable in direct reclaim path
> 
> 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@jp.fujitsu.com>
>   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: Rik van Riel <riel@redhat.com>
> Cc: M. Vefa Bicakci <bicave@superonline.com>
> Cc: stable@kernel.org
> Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
> Reviewed-by: Johannes Weiner <hannes@cmpxchg.org>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
> ---
>  mm/vmscan.c |   46 ++++++++++++++++++++++++++++++++++++++--------
>  1 files changed, 38 insertions(+), 8 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 7870893..ecae0ef 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1877,12 +1877,11 @@ 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) {
> @@ -1900,8 +1899,41 @@ static bool shrink_zones(int priority, struct zonelist *zonelist,
>                 }
> 
>                 shrink_zone(priority, zone, sc);
> -               all_unreclaimable = false;
>         }
> +}
> +
> +static bool zone_reclaimable(struct zone *zone)
> +{
> +       return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
> +}
> +
> +/*
> + * As hibernation is going on, kswapd is freezed so that it can't mark
> + * the zone into all_unreclaimable. It can't handle OOM during hibernation.
> + * So let's check zone's unreclaimable in direct reclaim as well as kswapd.
> + */
> +static 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_reclaimable(zone)) {
> +                       all_unreclaimable = false;
> +                       break;
> +               }
> +       }
> +
>         return all_unreclaimable;
>  }
> 
> @@ -1925,7 +1957,6 @@ 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;
> @@ -1942,7 +1973,7 @@ 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
> @@ -2004,7 +2035,7 @@ 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;
> @@ -2270,8 +2301,7 @@ loop_again:
>                         total_scanned += sc.nr_scanned;
>                         if (zone->all_unreclaimable)
>                                 continue;
> -                       if (nr_slab == 0 &&
> -                           zone->pages_scanned >= (zone_reclaimable_pages(zone) * 6))
> +                       if (nr_slab == 0 && !zone_reclaimable(zone))
>                                 zone->all_unreclaimable = 1;
>                         /*
>                          * If we've done a decent amount of scanning and
>