On 01/12/16 05:30, Michal Hocko wrote:
> On Wed 30-11-16 13:16:53, Johannes Weiner wrote:
>> Hi Michael,
>>
>> On Wed, Nov 30, 2016 at 06:00:40PM +0100, Michal Hocko wrote:
> [...]
>>> diff --git a/mm/workingset.c b/mm/workingset.c
>>> index 617475f529f4..0f07522c5c0e 100644
>>> --- a/mm/workingset.c
>>> +++ b/mm/workingset.c
>>> @@ -348,7 +348,7 @@ static unsigned long count_shadow_nodes(struct shrinker *shrinker,
>>> shadow_nodes = list_lru_shrink_count(&workingset_shadow_nodes, sc);
>>> local_irq_enable();
>>>
>>> - if (memcg_kmem_enabled()) {
>>> + if (memcg_kmem_enabled() && sc->memcg) {
>>> pages = mem_cgroup_node_nr_lru_pages(sc->memcg, sc->nid,
>>> LRU_ALL_FILE);
>>> } else {
>>
>> If we do that, I'd remove the racy memcg_kmem_enabled() check
>> altogether and just check for whether we have a memcg or not.
>
> But that would make this a memcg aware shrinker even when kmem is not
> enabled...
>
> But now that I am looking into the code
> shrink_slab:
> if (memcg_kmem_enabled() &&
> !!memcg != !!(shrinker->flags & SHRINKER_MEMCG_AWARE))
> continue;
>
> this should be taken care of already. So sc->memcg should be indeed
> sufficient. So unless I am missing something I will respin my local
> patch and post it later after the reporter has some time to test the
> current one.
>
I did a quick dis-assembly of the code
R9 and RDI are NULL and the instruction seems to be
mov rsi, [rdi+r9*8+0x400]
RDI is NULL, sc->memcg is NULL, which indicates global reclaim
The check referred to earlier
/*
* If kernel memory accounting is disabled, we ignore
* SHRINKER_MEMCG_AWARE flag and call all shrinkers
* passing NULL for memcg.
*/
if (memcg_kmem_enabled() &&
!!memcg != !!(shrinker->flags & SHRINKER_MEMCG_AWARE))
continue;
So we do pass NULL for memcg
A check for sc->memcg should be enough in count_shadow_nodes and a VM_BUG_ON
for memcg == NULL in mem_cgroup_node_nr_lru_pages would be nice
Balbir Singh.
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