Re: Kernel falls apart under light memory pressure (i.e. linking vmlinux)

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

> 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);
        }
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-----------------------------------------------------------------------------------------------------
bool should_reclaim_stall()
{
 (snip)

        /* Only stall on lumpy reclaim */
        if (sc->reclaim_mode & RECLAIM_MODE_SINGLE)   /// and here
                return false;
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