[PATCH] mm: vmscan: protect shrinker idr replace with CONFIG_MEMCG

[PATCH] mm: vmscan: protect shrinker idr replace with CONFIG_MEMCG

[Yang Shi]

Since commit 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 ("mm: shrinker:
make shrinker not depend on memcg kmem"), shrinkers' idr is protected by
CONFIG_MEMCG instead of CONFIG_MEMCG_KMEM, so it makes no sense to
protect shrinker idr replace with CONFIG_MEMCG_KMEM.

Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Roman Gushchin <guro@fb.com>
Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
---
 mm/vmscan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index ee4eecc..e7f10c4 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -422,7 +422,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
 {
 	down_write(&shrinker_rwsem);
 	list_add_tail(&shrinker->list, &shrinker_list);
-#ifdef CONFIG_MEMCG_KMEM
+#ifdef CONFIG_MEMCG
 	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
 		idr_replace(&shrinker_idr, shrinker, shrinker->id);
 #endif
-- 
1.8.3.1

Re: [PATCH] mm: vmscan: protect shrinker idr replace with CONFIG_MEMCG

[Kirill Tkhai]

On 04.12.2019 22:16, Yang Shi wrote:
> Since commit 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 ("mm: shrinker:
> make shrinker not depend on memcg kmem"), shrinkers' idr is protected by
> CONFIG_MEMCG instead of CONFIG_MEMCG_KMEM, so it makes no sense to
> protect shrinker idr replace with CONFIG_MEMCG_KMEM.
> 
> Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Shakeel Butt <shakeelb@google.com>
> Cc: Roman Gushchin <guro@fb.com>
> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>

It looks like that in CONFIG_SLOB case we do not even call some shrinkers
for subordinate mem cgroups (i.e., we don't call deferred_split_shrinker),
since they never become completely registered.

Fixes: 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 ("mm: shrinker: make shrinker not depend on memcg kmem")
Reviewed-by: Kirill Tkhai <ktkhai@virtuozzo.com>

> ---
>  mm/vmscan.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index ee4eecc..e7f10c4 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -422,7 +422,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
>  {
>  	down_write(&shrinker_rwsem);
>  	list_add_tail(&shrinker->list, &shrinker_list);
> -#ifdef CONFIG_MEMCG_KMEM
> +#ifdef CONFIG_MEMCG
>  	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
>  		idr_replace(&shrinker_idr, shrinker, shrinker->id);
>  #endif
> 

Re: [PATCH] mm: vmscan: protect shrinker idr replace with CONFIG_MEMCG

[Michal Hocko]

On Thu 05-12-19 11:23:28, Kirill Tkhai wrote:
> On 04.12.2019 22:16, Yang Shi wrote:
> > Since commit 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 ("mm: shrinker:
> > make shrinker not depend on memcg kmem"), shrinkers' idr is protected by
> > CONFIG_MEMCG instead of CONFIG_MEMCG_KMEM, so it makes no sense to
> > protect shrinker idr replace with CONFIG_MEMCG_KMEM.
> > 
> > Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
> > Cc: Johannes Weiner <hannes@cmpxchg.org>
> > Cc: Michal Hocko <mhocko@suse.com>
> > Cc: Shakeel Butt <shakeelb@google.com>
> > Cc: Roman Gushchin <guro@fb.com>
> > Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
> 
> It looks like that in CONFIG_SLOB case we do not even call some shrinkers
> for subordinate mem cgroups (i.e., we don't call deferred_split_shrinker),
> since they never become completely registered.
> 
> Fixes: 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 ("mm: shrinker: make shrinker not depend on memcg kmem")

I am confused. Why the Fixes tag? Nothing should be really broken with
KMEM config guard right?

This is a mere clean up AFAICS.

> Reviewed-by: Kirill Tkhai <ktkhai@virtuozzo.com>
> 
> > ---
> >  mm/vmscan.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index ee4eecc..e7f10c4 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -422,7 +422,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
> >  {
> >  	down_write(&shrinker_rwsem);
> >  	list_add_tail(&shrinker->list, &shrinker_list);
> > -#ifdef CONFIG_MEMCG_KMEM
> > +#ifdef CONFIG_MEMCG
> >  	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> >  		idr_replace(&shrinker_idr, shrinker, shrinker->id);
> >  #endif
> > 

-- 
Michal Hocko
SUSE Labs

Re: [PATCH] mm: vmscan: protect shrinker idr replace with CONFIG_MEMCG

[Kirill Tkhai]

On 05.12.2019 12:43, Michal Hocko wrote:
> On Thu 05-12-19 11:23:28, Kirill Tkhai wrote:
>> On 04.12.2019 22:16, Yang Shi wrote:
>>> Since commit 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 ("mm: shrinker:
>>> make shrinker not depend on memcg kmem"), shrinkers' idr is protected by
>>> CONFIG_MEMCG instead of CONFIG_MEMCG_KMEM, so it makes no sense to
>>> protect shrinker idr replace with CONFIG_MEMCG_KMEM.
>>>
>>> Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
>>> Cc: Johannes Weiner <hannes@cmpxchg.org>
>>> Cc: Michal Hocko <mhocko@suse.com>
>>> Cc: Shakeel Butt <shakeelb@google.com>
>>> Cc: Roman Gushchin <guro@fb.com>
>>> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
>>
>> It looks like that in CONFIG_SLOB case we do not even call some shrinkers
>> for subordinate mem cgroups (i.e., we don't call deferred_split_shrinker),
>> since they never become completely registered.
>>
>> Fixes: 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 ("mm: shrinker: make shrinker not depend on memcg kmem")
> 
> I am confused. Why the Fixes tag? Nothing should be really broken with
> KMEM config guard right?

idr_replace() is disabled in CONFIG_MEMCG && CONFIG_SLOB case, and this is
wrong.

0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 goes in the series, which enables
shrinker_idr infrastructure for huge_memory.c's deferred_split_shrinker
in CONFIG_MEMCG case. Previously, all SHRINKER_MEMCG_AWARE shrinkers were
based on LRUs, and they remain to base of CONFIG_MEMCG_KMEM.
But deferred_split_shrinker is an exception.

In CONFIG_MEMCG && CONFIG_SLOB case, shrinker_idr contains only shrinker,
and it is deferred_split_shrinker. But it is never actually called, since
idr_replace() is never compiled. deferred_split_shrinker all the time is
staying in half-registered state, and it's never called for subordinate
mem cgroups.

So, this is a BUG, and this should go to stable.

> This is a mere clean up AFAICS.
> 
>> Reviewed-by: Kirill Tkhai <ktkhai@virtuozzo.com>
>>
>>> ---
>>>  mm/vmscan.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>>> index ee4eecc..e7f10c4 100644
>>> --- a/mm/vmscan.c
>>> +++ b/mm/vmscan.c
>>> @@ -422,7 +422,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
>>>  {
>>>  	down_write(&shrinker_rwsem);
>>>  	list_add_tail(&shrinker->list, &shrinker_list);
>>> -#ifdef CONFIG_MEMCG_KMEM
>>> +#ifdef CONFIG_MEMCG
>>>  	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
>>>  		idr_replace(&shrinker_idr, shrinker, shrinker->id);
>>>  #endif
>>>
> 

Re: [PATCH] mm: vmscan: protect shrinker idr replace with CONFIG_MEMCG

[Kirill Tkhai]

On 05.12.2019 13:00, Kirill Tkhai wrote:
> On 05.12.2019 12:43, Michal Hocko wrote:
>> On Thu 05-12-19 11:23:28, Kirill Tkhai wrote:
>>> On 04.12.2019 22:16, Yang Shi wrote:
>>>> Since commit 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 ("mm: shrinker:
>>>> make shrinker not depend on memcg kmem"), shrinkers' idr is protected by
>>>> CONFIG_MEMCG instead of CONFIG_MEMCG_KMEM, so it makes no sense to
>>>> protect shrinker idr replace with CONFIG_MEMCG_KMEM.
>>>>
>>>> Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
>>>> Cc: Johannes Weiner <hannes@cmpxchg.org>
>>>> Cc: Michal Hocko <mhocko@suse.com>
>>>> Cc: Shakeel Butt <shakeelb@google.com>
>>>> Cc: Roman Gushchin <guro@fb.com>
>>>> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
>>>
>>> It looks like that in CONFIG_SLOB case we do not even call some shrinkers
>>> for subordinate mem cgroups (i.e., we don't call deferred_split_shrinker),
>>> since they never become completely registered.
>>>
>>> Fixes: 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 ("mm: shrinker: make shrinker not depend on memcg kmem")
>>
>> I am confused. Why the Fixes tag? Nothing should be really broken with
>> KMEM config guard right?
> 
> idr_replace() is disabled in CONFIG_MEMCG && CONFIG_SLOB case, and this is
> wrong.
> 
> 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 goes in the series, which enables
> shrinker_idr infrastructure for huge_memory.c's deferred_split_shrinker
> in CONFIG_MEMCG case. Previously, all SHRINKER_MEMCG_AWARE shrinkers were
> based on LRUs, and they remain to base of CONFIG_MEMCG_KMEM.
> But deferred_split_shrinker is an exception.
> 
> In CONFIG_MEMCG && CONFIG_SLOB case, shrinker_idr contains only shrinker,
> and it is deferred_split_shrinker. But it is never actually called, since
> idr_replace() is never compiled. deferred_split_shrinker all the time is
> staying in half-registered state, and it's never called for subordinate
> mem cgroups.
> 
> So, this is a BUG, and this should go to stable.

The visible effect is that deferred_split_shrinker is never called
from shrink_slab() for subordinate mem cgroups. It's called only
for root_mem_cgroup.

>> This is a mere clean up AFAICS.
>>
>>> Reviewed-by: Kirill Tkhai <ktkhai@virtuozzo.com>
>>>
>>>> ---
>>>>  mm/vmscan.c | 2 +-
>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>>>> index ee4eecc..e7f10c4 100644
>>>> --- a/mm/vmscan.c
>>>> +++ b/mm/vmscan.c
>>>> @@ -422,7 +422,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
>>>>  {
>>>>  	down_write(&shrinker_rwsem);
>>>>  	list_add_tail(&shrinker->list, &shrinker_list);
>>>> -#ifdef CONFIG_MEMCG_KMEM
>>>> +#ifdef CONFIG_MEMCG
>>>>  	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
>>>>  		idr_replace(&shrinker_idr, shrinker, shrinker->id);
>>>>  #endif
>>>>
>>
> 

Re: [PATCH] mm: vmscan: protect shrinker idr replace with CONFIG_MEMCG

[Yang Shi]

On 12/5/19 2:11 AM, Kirill Tkhai wrote:
> On 05.12.2019 13:00, Kirill Tkhai wrote:
>> On 05.12.2019 12:43, Michal Hocko wrote:
>>> On Thu 05-12-19 11:23:28, Kirill Tkhai wrote:
>>>> On 04.12.2019 22:16, Yang Shi wrote:
>>>>> Since commit 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 ("mm: shrinker:
>>>>> make shrinker not depend on memcg kmem"), shrinkers' idr is protected by
>>>>> CONFIG_MEMCG instead of CONFIG_MEMCG_KMEM, so it makes no sense to
>>>>> protect shrinker idr replace with CONFIG_MEMCG_KMEM.
>>>>>
>>>>> Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
>>>>> Cc: Johannes Weiner <hannes@cmpxchg.org>
>>>>> Cc: Michal Hocko <mhocko@suse.com>
>>>>> Cc: Shakeel Butt <shakeelb@google.com>
>>>>> Cc: Roman Gushchin <guro@fb.com>
>>>>> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
>>>> It looks like that in CONFIG_SLOB case we do not even call some shrinkers
>>>> for subordinate mem cgroups (i.e., we don't call deferred_split_shrinker),
>>>> since they never become completely registered.
>>>>
>>>> Fixes: 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 ("mm: shrinker: make shrinker not depend on memcg kmem")
>>> I am confused. Why the Fixes tag? Nothing should be really broken with
>>> KMEM config guard right?
>> idr_replace() is disabled in CONFIG_MEMCG && CONFIG_SLOB case, and this is
>> wrong.
>>
>> 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 goes in the series, which enables
>> shrinker_idr infrastructure for huge_memory.c's deferred_split_shrinker
>> in CONFIG_MEMCG case. Previously, all SHRINKER_MEMCG_AWARE shrinkers were
>> based on LRUs, and they remain to base of CONFIG_MEMCG_KMEM.
>> But deferred_split_shrinker is an exception.
>>
>> In CONFIG_MEMCG && CONFIG_SLOB case, shrinker_idr contains only shrinker,
>> and it is deferred_split_shrinker. But it is never actually called, since
>> idr_replace() is never compiled. deferred_split_shrinker all the time is
>> staying in half-registered state, and it's never called for subordinate
>> mem cgroups.
>>
>> So, this is a BUG, and this should go to stable.
> The visible effect is that deferred_split_shrinker is never called
> from shrink_slab() for subordinate mem cgroups. It's called only
> for root_mem_cgroup.

Thanks for noticing the SLOB case, I didn't realize it and thought it 
was just a cleanup too.

Will update the information and cc to stable list for v2.

>
>>> This is a mere clean up AFAICS.
>>>
>>>> Reviewed-by: Kirill Tkhai <ktkhai@virtuozzo.com>
>>>>
>>>>> ---
>>>>>   mm/vmscan.c | 2 +-
>>>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>>>>> index ee4eecc..e7f10c4 100644
>>>>> --- a/mm/vmscan.c
>>>>> +++ b/mm/vmscan.c
>>>>> @@ -422,7 +422,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
>>>>>   {
>>>>>   	down_write(&shrinker_rwsem);
>>>>>   	list_add_tail(&shrinker->list, &shrinker_list);
>>>>> -#ifdef CONFIG_MEMCG_KMEM
>>>>> +#ifdef CONFIG_MEMCG
>>>>>   	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
>>>>>   		idr_replace(&shrinker_idr, shrinker, shrinker->id);
>>>>>   #endif
>>>>>

Re: [PATCH] mm: vmscan: protect shrinker idr replace with CONFIG_MEMCG

[Michal Hocko]

On Thu 05-12-19 13:00:31, Kirill Tkhai wrote:
> On 05.12.2019 12:43, Michal Hocko wrote:
> > On Thu 05-12-19 11:23:28, Kirill Tkhai wrote:
> >> On 04.12.2019 22:16, Yang Shi wrote:
> >>> Since commit 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 ("mm: shrinker:
> >>> make shrinker not depend on memcg kmem"), shrinkers' idr is protected by
> >>> CONFIG_MEMCG instead of CONFIG_MEMCG_KMEM, so it makes no sense to
> >>> protect shrinker idr replace with CONFIG_MEMCG_KMEM.
> >>>
> >>> Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
> >>> Cc: Johannes Weiner <hannes@cmpxchg.org>
> >>> Cc: Michal Hocko <mhocko@suse.com>
> >>> Cc: Shakeel Butt <shakeelb@google.com>
> >>> Cc: Roman Gushchin <guro@fb.com>
> >>> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
> >>
> >> It looks like that in CONFIG_SLOB case we do not even call some shrinkers
> >> for subordinate mem cgroups (i.e., we don't call deferred_split_shrinker),
> >> since they never become completely registered.
> >>
> >> Fixes: 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 ("mm: shrinker: make shrinker not depend on memcg kmem")
> > 
> > I am confused. Why the Fixes tag? Nothing should be really broken with
> > KMEM config guard right?
> 
> idr_replace() is disabled in CONFIG_MEMCG && CONFIG_SLOB case, and this is
> wrong.
> 
> 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 goes in the series, which enables
> shrinker_idr infrastructure for huge_memory.c's deferred_split_shrinker
> in CONFIG_MEMCG case. Previously, all SHRINKER_MEMCG_AWARE shrinkers were
> based on LRUs, and they remain to base of CONFIG_MEMCG_KMEM.
> But deferred_split_shrinker is an exception.
> 
> In CONFIG_MEMCG && CONFIG_SLOB case, shrinker_idr contains only shrinker,
> and it is deferred_split_shrinker. But it is never actually called, since
> idr_replace() is never compiled. deferred_split_shrinker all the time is
> staying in half-registered state, and it's never called for subordinate
> mem cgroups.
> 
> So, this is a BUG, and this should go to stable.

OK, I see. The changelog should describe all that. Thanks for the
clarification.

> > This is a mere clean up AFAICS.
> > 
> >> Reviewed-by: Kirill Tkhai <ktkhai@virtuozzo.com>
> >>
> >>> ---
> >>>  mm/vmscan.c | 2 +-
> >>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>
> >>> diff --git a/mm/vmscan.c b/mm/vmscan.c
> >>> index ee4eecc..e7f10c4 100644
> >>> --- a/mm/vmscan.c
> >>> +++ b/mm/vmscan.c
> >>> @@ -422,7 +422,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
> >>>  {
> >>>  	down_write(&shrinker_rwsem);
> >>>  	list_add_tail(&shrinker->list, &shrinker_list);
> >>> -#ifdef CONFIG_MEMCG_KMEM
> >>> +#ifdef CONFIG_MEMCG
> >>>  	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> >>>  		idr_replace(&shrinker_idr, shrinker, shrinker->id);
> >>>  #endif
> >>>
> > 
> 

-- 
Michal Hocko
SUSE Labs

Re: [PATCH] mm: vmscan: protect shrinker idr replace with CONFIG_MEMCG

[Michal Hocko]

On Thu 05-12-19 03:16:18, Yang Shi wrote:
> Since commit 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 ("mm: shrinker:
> make shrinker not depend on memcg kmem"), shrinkers' idr is protected by
> CONFIG_MEMCG instead of CONFIG_MEMCG_KMEM, so it makes no sense to
> protect shrinker idr replace with CONFIG_MEMCG_KMEM.
> 
> Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Shakeel Butt <shakeelb@google.com>
> Cc: Roman Gushchin <guro@fb.com>
> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  mm/vmscan.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index ee4eecc..e7f10c4 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -422,7 +422,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
>  {
>  	down_write(&shrinker_rwsem);
>  	list_add_tail(&shrinker->list, &shrinker_list);
> -#ifdef CONFIG_MEMCG_KMEM
> +#ifdef CONFIG_MEMCG
>  	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
>  		idr_replace(&shrinker_idr, shrinker, shrinker->id);
>  #endif
> -- 
> 1.8.3.1

-- 
Michal Hocko
SUSE Labs