Re: memory-controller patch fails to boot in qemu [mmotm]

[Hugh Dickins <hugh.dickins@tiscali.co.uk>]

On Sun, 2 Aug 2009, Balbir Singh wrote:
> * Hugh Dickins <hugh.dickins@tiscali.co.uk> [2009-08-01 23:09:09]:
> > 
> > Hmm, this a weird function, passed an argument just to tell it to do
> > nothing.  Perhaps a placeholder for something more sensible to come?
> 
> The argument is passed a result of a function, It no-ops quite
> frequently for the root cgroup.

The more often it no-ops, the sillier it is to be called in
the first place: here's an updated patch which fixes that too.


[PATCH mmotm] memory controller: soft limit organize cgroups v9 fix

CONFIG_CGROUP_MEM_RES_CTLR=y CONFIG_PREEMPT=y mmotm fails to boot:
Kernel panic - not syncing: No init found; after lots of scheduling
while atomics, starting from when async_thread does sd_probe_async.

mem_cgroup_soft_limit_check() was doing an unbalanced get_cpu():
don't get_cpu if we won't need it, and put_cpu if we did get_cpu.

And fix the silliness of passing it an "over_soft_limit" argument
that just tells it to return false when false.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
---
Fix to memory-controller-soft-limit-organize-cgroups-v9.patch

 mm/memcontrol.c |   14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

--- mmotm/mm/memcontrol.c	2009-08-01 05:48:08.000000000 +0100
+++ linux/mm/memcontrol.c	2009-08-02 16:56:02.000000000 +0100
@@ -371,23 +371,21 @@ mem_cgroup_remove_exceeded(struct mem_cg
 	spin_unlock(&mctz->lock);
 }
 
-static bool mem_cgroup_soft_limit_check(struct mem_cgroup *mem,
-					bool over_soft_limit)
+static bool mem_cgroup_soft_limit_check(struct mem_cgroup *mem)
 {
 	bool ret = false;
-	int cpu = get_cpu();
+	int cpu;
 	s64 val;
 	struct mem_cgroup_stat_cpu *cpustat;
 
-	if (!over_soft_limit)
-		return ret;
-
+	cpu = get_cpu();
 	cpustat = &mem->stat.cpustat[cpu];
 	val = __mem_cgroup_stat_read_local(cpustat, MEM_CGROUP_STAT_EVENTS);
 	if (unlikely(val > SOFTLIMIT_EVENTS_THRESH)) {
 		__mem_cgroup_stat_reset_safe(cpustat, MEM_CGROUP_STAT_EVENTS);
 		ret = true;
 	}
+	put_cpu();
 	return ret;
 }
 
@@ -1342,7 +1340,7 @@ static int __mem_cgroup_try_charge(struc
 	if (soft_fail_res) {
 		mem_over_soft_limit =
 			mem_cgroup_from_res_counter(soft_fail_res, res);
-		if (mem_cgroup_soft_limit_check(mem_over_soft_limit, true))
+		if (mem_cgroup_soft_limit_check(mem_over_soft_limit))
 			mem_cgroup_update_tree(mem_over_soft_limit, page);
 	}
 	return 0;
@@ -1873,7 +1871,7 @@ __mem_cgroup_uncharge_common(struct page
 	mz = page_cgroup_zoneinfo(pc);
 	unlock_page_cgroup(pc);
 
-	if (mem_cgroup_soft_limit_check(mem, soft_limit_excess))
+	if (soft_limit_excess && mem_cgroup_soft_limit_check(mem))
 		mem_cgroup_update_tree(mem, page);
 	/* at swapout, this memcg will be accessed to record to swap */
 	if (ctype != MEM_CGROUP_CHARGE_TYPE_SWAPOUT)