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Date: Fri, 11 Mar 2011 09:18:21 +0900
From: Minchan Kim <minchan.kim@...il.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Andrew Vagin <avagin@...il.com>,
Andrey Vagin <avagin@...nvz.org>, Mel Gorman <mel@....ul.ie>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: check zone->all_unreclaimable in all_unreclaimable()
On Fri, Mar 11, 2011 at 8:58 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
> On Thu, 10 Mar 2011 15:58:29 +0900
> Minchan Kim <minchan.kim@...il.com> wrote:
>
>> Hi Kame,
>>
>> Sorry for late response.
>> I had a time to test this issue shortly because these day I am very busy.
>> This issue was interesting to me.
>> So I hope taking a time for enough testing when I have a time.
>> I should find out root cause of livelock.
>>
>
> Thanks. I and Kosaki-san reproduced the bug with swapless system.
> Now, Kosaki-san is digging and found some issue with scheduler boost at OOM
> and lack of enough "wait" in vmscan.c.
>
> I myself made patch like attached one. This works well for returning TRUE at
> all_unreclaimable() but livelock(deadlock?) still happens.
I saw the deadlock.
It seems to happen by following code by my quick debug but not sure. I
need to investigate further but don't have a time now. :(
* Note: this may have a chance of deadlock if it gets
* blocked waiting for another task which itself is waiting
* for memory. Is there a better alternative?
*/
if (test_tsk_thread_flag(p, TIF_MEMDIE))
return ERR_PTR(-1UL);
It would be wait to die the task forever without another victim selection.
If it's right, It's a known BUG and we have no choice until now. Hmm.
> I wonder vmscan itself isn't a key for fixing issue.
I agree.
> Then, I'd like to wait for Kosaki-san's answer ;)
Me, too. :)
>
> I'm now wondering how to catch fork-bomb and stop it (without using cgroup).
Yes. Fork throttling without cgroup is very important.
And as off-topic, mem_notify without memcontrol you mentioned is
important to embedded people, I gues.
> I think the problem is that fork-bomb is faster than killall...
And deadlock problem I mentioned.
>
> Thanks,
> -Kame
Thanks for the investigation, Kame.
> ==
>
> This is just a debug patch.
>
> ---
> mm/vmscan.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 54 insertions(+), 4 deletions(-)
>
> Index: mmotm-0303/mm/vmscan.c
> ===================================================================
> --- mmotm-0303.orig/mm/vmscan.c
> +++ mmotm-0303/mm/vmscan.c
> @@ -1983,9 +1983,55 @@ static void shrink_zones(int priority, s
> }
> }
>
> -static bool zone_reclaimable(struct zone *zone)
> +static bool zone_seems_empty(struct zone *zone, struct scan_control *sc)
> {
> - return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
> + unsigned long nr, wmark, free, isolated, lru;
> +
> + /*
> + * If scanned, zone->pages_scanned is incremented and this can
> + * trigger OOM.
> + */
> + if (sc->nr_scanned)
> + return false;
> +
> + free = zone_page_state(zone, NR_FREE_PAGES);
> + isolated = zone_page_state(zone, NR_ISOLATED_FILE);
> + if (nr_swap_pages)
> + isolated += zone_page_state(zone, NR_ISOLATED_ANON);
> +
> + /* In we cannot do scan, don't count LRU pages. */
> + if (!zone->all_unreclaimable) {
> + lru = zone_page_state(zone, NR_ACTIVE_FILE);
> + lru += zone_page_state(zone, NR_INACTIVE_FILE);
> + if (nr_swap_pages) {
> + lru += zone_page_state(zone, NR_ACTIVE_ANON);
> + lru += zone_page_state(zone, NR_INACTIVE_ANON);
> + }
> + } else
> + lru = 0;
> + nr = free + isolated + lru;
> + wmark = min_wmark_pages(zone);
> + wmark += zone->lowmem_reserve[gfp_zone(sc->gfp_mask)];
> + wmark += 1 << sc->order;
> + printk("thread %d/%ld all %d scanned %ld pages %ld/%ld/%ld/%ld/%ld/%ld\n",
> + current->pid, sc->nr_scanned, zone->all_unreclaimable,
> + zone->pages_scanned,
> + nr,free,isolated,lru,
> + zone_reclaimable_pages(zone), wmark);
> + /*
> + * In some case (especially noswap), almost all page cache are paged out
> + * and we'll see the amount of reclaimable+free pages is smaller than
> + * zone->min. In this case, we canoot expect any recovery other
> + * than OOM-KILL. We can't reclaim memory enough for usual tasks.
> + */
> +
> + return nr <= wmark;
> +}
> +
> +static bool zone_reclaimable(struct zone *zone, struct scan_control *sc)
> +{
> + /* zone_reclaimable_pages() can return 0, we need <= */
> + return zone->pages_scanned <= zone_reclaimable_pages(zone) * 6;
> }
>
> /*
> @@ -2006,11 +2052,15 @@ static bool all_unreclaimable(struct zon
> continue;
> if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
> continue;
> - if (zone_reclaimable(zone)) {
> + if (zone_seems_empty(zone, sc))
> + continue;
> + if (zone_reclaimable(zone, sc)) {
> all_unreclaimable = false;
> break;
> }
> }
> + if (all_unreclaimable)
> + printk("all_unreclaimable() returns TRUE\n");
>
> return all_unreclaimable;
> }
> @@ -2456,7 +2506,7 @@ loop_again:
> if (zone->all_unreclaimable)
> continue;
> if (!compaction && nr_slab == 0 &&
> - !zone_reclaimable(zone))
> + !zone_reclaimable(zone, &sc))
> zone->all_unreclaimable = 1;
> /*
> * If we've done a decent amount of scanning and
>
>
--
Kind regards,
Minchan Kim
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