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SubjectRe: memory-controller patch fails to boot in qemu [mmotm]
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Hugh Dickins wrote:
> 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>

nice fix, thank you very much.

Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

> ---
> 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)
>




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