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    SubjectRe: Kernel falls apart under light memory pressure (i.e. linking vmlinux)
    On Sat, May 21, 2011 at 10:44 AM, Minchan Kim <minchan.kim@gmail.com> wrote:
    > Hi Andrew.
    >
    > On Sat, May 21, 2011 at 10:34 PM, Andrew Lutomirski <luto@mit.edu> wrote:
    >> On Sat, May 21, 2011 at 8:04 AM, KOSAKI Motohiro
    >> <kosaki.motohiro@jp.fujitsu.com> wrote:
    >>>> diff --git a/mm/vmscan.c b/mm/vmscan.c
    >>>> index 3f44b81..d1dabc9 100644
    >>>> @@ -1426,8 +1437,13 @@ shrink_inactive_list(unsigned long nr_to_scan,
    >>>> struct zone *zone,
    >>>>
    >>>>        /* Check if we should syncronously wait for writeback */
    >>>>        if (should_reclaim_stall(nr_taken, nr_reclaimed, priority, sc)) {
    >>>> +               unsigned long nr_active, old_nr_scanned;
    >>>>                set_reclaim_mode(priority, sc, true);
    >>>> +               nr_active = clear_active_flags(&page_list, NULL);
    >>>> +               count_vm_events(PGDEACTIVATE, nr_active);
    >>>> +               old_nr_scanned = sc->nr_scanned;
    >>>>                nr_reclaimed += shrink_page_list(&page_list, zone, sc);
    >>>> +               sc->nr_scanned = old_nr_scanned;
    >>>>        }
    >>>>
    >>>>        local_irq_disable();
    >>>>
    >>>> I just tested 2.6.38.6 with the attached patch.  It survived dirty_ram
    >>>> and test_mempressure without any problems other than slowness, but
    >>>> when I hit ctrl-c to stop test_mempressure, I got the attached oom.
    >>>
    >>> Minchan,
    >>>
    >>> I'm confused now.
    >>> If pages got SetPageActive(), should_reclaim_stall() should never return true.
    >>> Can you please explain which bad scenario was happen?
    >>>
    >>> -----------------------------------------------------------------------------------------------------
    >>> static void reset_reclaim_mode(struct scan_control *sc)
    >>> {
    >>>        sc->reclaim_mode = RECLAIM_MODE_SINGLE | RECLAIM_MODE_ASYNC;
    >>> }
    >>>
    >>> shrink_page_list()
    >>> {
    >>>  (snip)
    >>>  activate_locked:
    >>>                SetPageActive(page);
    >>>                pgactivate++;
    >>>                unlock_page(page);
    >>>                reset_reclaim_mode(sc);                  /// here
    >>>                list_add(&page->lru, &ret_pages);
    >>>        }
    >>> -----------------------------------------------------------------------------------------------------
    >>>
    >>>
    >>> -----------------------------------------------------------------------------------------------------
    >>> bool should_reclaim_stall()
    >>> {
    >>>  (snip)
    >>>
    >>>        /* Only stall on lumpy reclaim */
    >>>        if (sc->reclaim_mode & RECLAIM_MODE_SINGLE)   /// and here
    >>>                return false;
    >>> -----------------------------------------------------------------------------------------------------
    >>>
    >>
    >> I did some tracing and the oops happens from the second call to
    >> shrink_page_list after should_reclaim_stall returns true and it hits
    >> the same pages in the same order that the earlier call just finished
    >> calling SetPageActive on.  I have *not* confirmed that the two calls
    >> happened from the same call to shrink_inactive_list, but something's
    >> certainly wrong in there.
    >>
    >> This is very easy to reproduce on my laptop.
    >
    > I would like to confirm this problem.
    > Could you show the diff of 2.6.38.6 with current your 2.6.38.6 + alpha?
    > (ie, I would like to know that what patches you add up on vanilla
    > 2.6.38.6 to reproduce this problem)
    > I believe you added my crap below patch. Right?
    >
    > diff --git a/mm/vmscan.c b/mm/vmscan.c
    > index 292582c..69d317e 100644
    > --- a/mm/vmscan.c
    > +++ b/mm/vmscan.c
    > @@ -311,7 +311,8 @@ static void set_reclaim_mode(int priority, struct
    > scan_control *sc,
    >        */
    >       if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
    >               sc->reclaim_mode |= syncmode;
    > -       else if (sc->order && priority < DEF_PRIORITY - 2)
    > +       else if ((sc->order && priority < DEF_PRIORITY - 2) ||
    > +                               prioiry <= DEF_PRIORITY / 3)
    >               sc->reclaim_mode |= syncmode;
    >       else
    >               sc->reclaim_mode = RECLAIM_MODE_SINGLE | RECLAIM_MODE_ASYNC;
    > @@ -1349,10 +1350,6 @@ static inline bool
    > should_reclaim_stall(unsigned long nr_taken,
    >       if (current_is_kswapd())
    >               return false;
    >
    > -       /* Only stall on lumpy reclaim */
    > -       if (sc->reclaim_mode & RECLAIM_MODE_SINGLE)
    > -               return false;
    > -

    Bah. It's this last hunk. Without this I can't reproduce the oops.
    With this hunk, the reset_reclaim_mode doesn't work and
    shrink_page_list is incorrectly called twice.

    So we're back to the original problem...

    --Andy
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