Re: [PATCH 3/3] mm: slub: Default slub_max_order to 0

[James Bottomley]

On Thu, 2011-05-12 at 15:04 -0500, James Bottomley wrote:
> Confirmed, I'm afraid ... I can trigger the problem with all three
> patches under PREEMPT.  It's not a hang this time, it's just kswapd
> taking 100% system time on 1 CPU and it won't calm down after I unload
> the system.

Just on a "if you don't know what's wrong poke about and see" basis, I
sliced out all the complex logic in sleeping_prematurely() and, as far
as I can tell, it cures the problem behaviour.  I've loaded up the
system, and taken the tar load generator through three runs without
producing a spinning kswapd (this is PREEMPT).  I'll try with a
non-PREEMPT kernel shortly.

What this seems to say is that there's a problem with the complex logic
in sleeping_prematurely().  I'm pretty sure hacking up
sleeping_prematurely() just to dump all the calculations is the wrong
thing to do, but perhaps someone can see what the right thing is ...

By the way, I stripped off all the patches, so this is a plain old
2.6.38.6 kernel with the default FC15 config.

James

---

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 0665520..1bdea7d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2255,6 +2255,8 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
 	if (remaining)
 		return true;
 
+	return false;
+
 	/* Check the watermark levels */
 	for (i = 0; i < pgdat->nr_zones; i++) {
 		struct zone *zone = pgdat->node_zones + i;


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