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    Subject[PATCH] vmscan: check all_unreclaimable in direct reclaim path
    Date
    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: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
    Cc: M. Vefa Bicakci <bicave@superonline.com>
    Cc: stable@kernel.org
    Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
    ---
    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;
    --
    1.7.0.5


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