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

From: Rafael J. Wysocki
Date: Sun Sep 05 2010 - 18:31:22 EST


On Sunday, September 05, 2010, 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>

Acked-by: Rafael J. Wysocki <rjw@xxxxxxx>

> ---
> 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)) {
> + 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;
>

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