Messages in this thread Patch in this message | | | Date | Wed, 20 Jul 2011 01:51:55 +0900 | From | Minchan Kim <> | Subject | Re: [PATCH]vmscan: fix a livelock in kswapd |
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On Tue, Jul 19, 2011 at 04:53:04PM +0800, Shaohua Li wrote: > On Tue, 2011-07-19 at 16:45 +0800, Minchan Kim wrote: > > On Tue, Jul 19, 2011 at 4:09 PM, Shaohua Li <shaohua.li@intel.com> wrote: > > > I'm running a workload which triggers a lot of swap in a machine with 4 nodes. > > > After I kill the workload, I found a kswapd livelock. Sometimes kswapd3 or > > > kswapd2 are keeping running and I can't access filesystem, but most memory is > > > free. This looks like a regression since commit 08951e545918c159. > > > > Could you tell me what is 08951e545918c159? > > You mean [ebd64e21ec5a, > > mm-vmscan-only-read-new_classzone_idx-from-pgdat-when-reclaiming-successfully] > > ? > ha, sorry, I should copy the commit title. > 08951e545918c159(mm: vmscan: correct check for kswapd sleeping in > sleeping_prematurely) >
I don't mean it. In my bogus git tree, I can't find it but I can look at it in repaired git tree. :) Anyway, I have a comment. Please look at below.
On Tue, Jul 19, 2011 at 03:09:27PM +0800, Shaohua Li wrote: > I'm running a workload which triggers a lot of swap in a machine with 4 nodes. > After I kill the workload, I found a kswapd livelock. Sometimes kswapd3 or > kswapd2 are keeping running and I can't access filesystem, but most memory is > free. This looks like a regression since commit 08951e545918c159. > Node 2 and 3 have only ZONE_NORMAL, but balance_pgdat() will return 0 for > classzone_idx. The reason is end_zone in balance_pgdat() is 0 by default, if > all zones have watermark ok, end_zone will keep 0. > Later sleeping_prematurely() always returns true. Because this is an order 3 > wakeup, and if classzone_idx is 0, both balanced_pages and present_pages > in pgdat_balanced() are 0.
Sigh. Yes.
> We add a special case here. If a zone has no page, we think it's balanced. This > fixes the livelock.
Yes. Your patch can fix it but I don't like that it adds handling special case. (Although Andrew merged quickly).
The problem is to return 0-classzone_idx if all zones was okay. So how about this?
This can change old behavior slightly. For example, if balance_pgdat calls with order-3 and all zones are okay about order-3, it will recheck order-0 as end_zone isn't 0 any more. But I think it's desriable side effect we have missed.
diff --git a/mm/vmscan.c b/mm/vmscan.c index 5ed24b9..cfef52b 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2389,7 +2389,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order, unsigned long balanced; int priority; int i; - int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */ + int end_zone = *classzone_idx; unsigned long total_scanned; struct reclaim_state *reclaim_state = current->reclaim_state; unsigned long nr_soft_reclaimed; -- Kinds regards, Minchan Kim
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