diff mbox series

[v3,05/11] mm: vmscan: use a new flag to indicate shrinker is registered

Message ID 20210105225817.1036378-6-shy828301@gmail.com (mailing list archive)
State New
Headers show
Series Make shrinker's nr_deferred memcg aware | expand

Commit Message

Yang Shi Jan. 5, 2021, 10:58 p.m. UTC
Currently registered shrinker is indicated by non-NULL shrinker->nr_deferred.
This approach is fine with nr_deferred at the shrinker level, but the following
patches will move MEMCG_AWARE shrinkers' nr_deferred to memcg level, so their
shrinker->nr_deferred would always be NULL.  This would prevent the shrinkers
from unregistering correctly.

Signed-off-by: Yang Shi <shy828301@gmail.com>
---
 include/linux/shrinker.h |  7 ++++---
 mm/vmscan.c              | 13 +++++++++----
 2 files changed, 13 insertions(+), 7 deletions(-)

Comments

Kirill Tkhai Jan. 6, 2021, 10:21 a.m. UTC | #1
On 06.01.2021 01:58, Yang Shi wrote:
> Currently registered shrinker is indicated by non-NULL shrinker->nr_deferred.
> This approach is fine with nr_deferred at the shrinker level, but the following
> patches will move MEMCG_AWARE shrinkers' nr_deferred to memcg level, so their
> shrinker->nr_deferred would always be NULL.  This would prevent the shrinkers
> from unregistering correctly.
> 
> Signed-off-by: Yang Shi <shy828301@gmail.com>
> ---
>  include/linux/shrinker.h |  7 ++++---
>  mm/vmscan.c              | 13 +++++++++----
>  2 files changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
> index 0f80123650e2..1eac79ce57d4 100644
> --- a/include/linux/shrinker.h
> +++ b/include/linux/shrinker.h
> @@ -79,13 +79,14 @@ struct shrinker {
>  #define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
>  
>  /* Flags */
> -#define SHRINKER_NUMA_AWARE	(1 << 0)
> -#define SHRINKER_MEMCG_AWARE	(1 << 1)
> +#define SHRINKER_REGISTERED	(1 << 0)
> +#define SHRINKER_NUMA_AWARE	(1 << 1)
> +#define SHRINKER_MEMCG_AWARE	(1 << 2)
>  /*
>   * It just makes sense when the shrinker is also MEMCG_AWARE for now,
>   * non-MEMCG_AWARE shrinker should not have this flag set.
>   */
> -#define SHRINKER_NONSLAB	(1 << 2)
> +#define SHRINKER_NONSLAB	(1 << 3)
>  
>  extern int prealloc_shrinker(struct shrinker *shrinker);
>  extern void register_shrinker_prepared(struct shrinker *shrinker);
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 8da765a85569..9761c7c27412 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -494,6 +494,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
>  	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
>  		idr_replace(&shrinker_idr, shrinker, shrinker->id);
>  #endif
> +	shrinker->flags |= SHRINKER_REGISTERED;

In case of we introduce this new flag, we should kill old flag SHRINKER_REGISTERING,
which are not needed anymore (we should you the new flag instead of that).

>  	up_write(&shrinker_rwsem);
>  }
>  
> @@ -513,13 +514,17 @@ EXPORT_SYMBOL(register_shrinker);
>   */
>  void unregister_shrinker(struct shrinker *shrinker)
>  {
> -	if (!shrinker->nr_deferred)
> -		return;
> -	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> -		unregister_memcg_shrinker(shrinker);
>  	down_write(&shrinker_rwsem);

I do not think there are some users which registration may race with unregistration.
So, I think we should check SHRINKER_REGISTERED unlocked similar to we used to check
shrinker->nr_deferred unlocked.

> +	if (!(shrinker->flags & SHRINKER_REGISTERED)) {
> +		up_write(&shrinker_rwsem);
> +		return;
> +	}
>  	list_del(&shrinker->list);
> +	shrinker->flags &= ~SHRINKER_REGISTERED;
>  	up_write(&shrinker_rwsem);
> +
> +	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> +		unregister_memcg_shrinker(shrinker);
>  	kfree(shrinker->nr_deferred);
>  	shrinker->nr_deferred = NULL;
>  }
>
Yang Shi Jan. 11, 2021, 6:17 p.m. UTC | #2
On Wed, Jan 6, 2021 at 2:22 AM Kirill Tkhai <ktkhai@virtuozzo.com> wrote:
>
> On 06.01.2021 01:58, Yang Shi wrote:
> > Currently registered shrinker is indicated by non-NULL shrinker->nr_deferred.
> > This approach is fine with nr_deferred at the shrinker level, but the following
> > patches will move MEMCG_AWARE shrinkers' nr_deferred to memcg level, so their
> > shrinker->nr_deferred would always be NULL.  This would prevent the shrinkers
> > from unregistering correctly.
> >
> > Signed-off-by: Yang Shi <shy828301@gmail.com>
> > ---
> >  include/linux/shrinker.h |  7 ++++---
> >  mm/vmscan.c              | 13 +++++++++----
> >  2 files changed, 13 insertions(+), 7 deletions(-)
> >
> > diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
> > index 0f80123650e2..1eac79ce57d4 100644
> > --- a/include/linux/shrinker.h
> > +++ b/include/linux/shrinker.h
> > @@ -79,13 +79,14 @@ struct shrinker {
> >  #define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
> >
> >  /* Flags */
> > -#define SHRINKER_NUMA_AWARE  (1 << 0)
> > -#define SHRINKER_MEMCG_AWARE (1 << 1)
> > +#define SHRINKER_REGISTERED  (1 << 0)
> > +#define SHRINKER_NUMA_AWARE  (1 << 1)
> > +#define SHRINKER_MEMCG_AWARE (1 << 2)
> >  /*
> >   * It just makes sense when the shrinker is also MEMCG_AWARE for now,
> >   * non-MEMCG_AWARE shrinker should not have this flag set.
> >   */
> > -#define SHRINKER_NONSLAB     (1 << 2)
> > +#define SHRINKER_NONSLAB     (1 << 3)
> >
> >  extern int prealloc_shrinker(struct shrinker *shrinker);
> >  extern void register_shrinker_prepared(struct shrinker *shrinker);
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 8da765a85569..9761c7c27412 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -494,6 +494,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
> >       if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> >               idr_replace(&shrinker_idr, shrinker, shrinker->id);
> >  #endif
> > +     shrinker->flags |= SHRINKER_REGISTERED;
>
> In case of we introduce this new flag, we should kill old flag SHRINKER_REGISTERING,
> which are not needed anymore (we should you the new flag instead of that).

The only think that I'm confused with is the check in
shrink_slab_memcg, it does:

shrinker = idr_find(&shrinker_idr, i);
if (unlikely(!shrinker || shrinker == SHRINKER_REGISTERING)) {

When allocating idr, the shrinker is associated with
SHRINKER_REGISTERING. But, shrink_slab_memcg does acquire read
shrinker_rwsem, and idr_alloc is called with holding write
shrinker_rwsem, so I'm supposed shrink_slab_memcg should never see
shrinker is registering. If so it seems easy to remove
SHRINKER_REGISTERING.

We just need change that check to:
!shrinker || !(shrinker->flags & SHRINKER_REGISTERED)

> >       up_write(&shrinker_rwsem);
> >  }
> >
> > @@ -513,13 +514,17 @@ EXPORT_SYMBOL(register_shrinker);
> >   */
> >  void unregister_shrinker(struct shrinker *shrinker)
> >  {
> > -     if (!shrinker->nr_deferred)
> > -             return;
> > -     if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> > -             unregister_memcg_shrinker(shrinker);
> >       down_write(&shrinker_rwsem);
>
> I do not think there are some users which registration may race with unregistration.
> So, I think we should check SHRINKER_REGISTERED unlocked similar to we used to check
> shrinker->nr_deferred unlocked.

Yes, I agree.

>
> > +     if (!(shrinker->flags & SHRINKER_REGISTERED)) {
> > +             up_write(&shrinker_rwsem);
> > +             return;
> > +     }
> >       list_del(&shrinker->list);
> > +     shrinker->flags &= ~SHRINKER_REGISTERED;
> >       up_write(&shrinker_rwsem);
> > +
> > +     if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> > +             unregister_memcg_shrinker(shrinker);
> >       kfree(shrinker->nr_deferred);
> >       shrinker->nr_deferred = NULL;
> >  }
> >
>
>
Kirill Tkhai Jan. 11, 2021, 9:37 p.m. UTC | #3
On 11.01.2021 21:17, Yang Shi wrote:
> On Wed, Jan 6, 2021 at 2:22 AM Kirill Tkhai <ktkhai@virtuozzo.com> wrote:
>>
>> On 06.01.2021 01:58, Yang Shi wrote:
>>> Currently registered shrinker is indicated by non-NULL shrinker->nr_deferred.
>>> This approach is fine with nr_deferred at the shrinker level, but the following
>>> patches will move MEMCG_AWARE shrinkers' nr_deferred to memcg level, so their
>>> shrinker->nr_deferred would always be NULL.  This would prevent the shrinkers
>>> from unregistering correctly.
>>>
>>> Signed-off-by: Yang Shi <shy828301@gmail.com>
>>> ---
>>>  include/linux/shrinker.h |  7 ++++---
>>>  mm/vmscan.c              | 13 +++++++++----
>>>  2 files changed, 13 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
>>> index 0f80123650e2..1eac79ce57d4 100644
>>> --- a/include/linux/shrinker.h
>>> +++ b/include/linux/shrinker.h
>>> @@ -79,13 +79,14 @@ struct shrinker {
>>>  #define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
>>>
>>>  /* Flags */
>>> -#define SHRINKER_NUMA_AWARE  (1 << 0)
>>> -#define SHRINKER_MEMCG_AWARE (1 << 1)
>>> +#define SHRINKER_REGISTERED  (1 << 0)
>>> +#define SHRINKER_NUMA_AWARE  (1 << 1)
>>> +#define SHRINKER_MEMCG_AWARE (1 << 2)
>>>  /*
>>>   * It just makes sense when the shrinker is also MEMCG_AWARE for now,
>>>   * non-MEMCG_AWARE shrinker should not have this flag set.
>>>   */
>>> -#define SHRINKER_NONSLAB     (1 << 2)
>>> +#define SHRINKER_NONSLAB     (1 << 3)
>>>
>>>  extern int prealloc_shrinker(struct shrinker *shrinker);
>>>  extern void register_shrinker_prepared(struct shrinker *shrinker);
>>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>>> index 8da765a85569..9761c7c27412 100644
>>> --- a/mm/vmscan.c
>>> +++ b/mm/vmscan.c
>>> @@ -494,6 +494,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
>>>       if (shrinker->flags & SHRINKER_MEMCG_AWARE)
>>>               idr_replace(&shrinker_idr, shrinker, shrinker->id);
>>>  #endif
>>> +     shrinker->flags |= SHRINKER_REGISTERED;
>>
>> In case of we introduce this new flag, we should kill old flag SHRINKER_REGISTERING,
>> which are not needed anymore (we should you the new flag instead of that).
> 
> The only think that I'm confused with is the check in
> shrink_slab_memcg, it does:
> 
> shrinker = idr_find(&shrinker_idr, i);
> if (unlikely(!shrinker || shrinker == SHRINKER_REGISTERING)) {
> 
> When allocating idr, the shrinker is associated with
> SHRINKER_REGISTERING. But, shrink_slab_memcg does acquire read
> shrinker_rwsem, and idr_alloc is called with holding write
> shrinker_rwsem, so I'm supposed shrink_slab_memcg should never see
> shrinker is registering.

After prealloc_shrinker() shrinker is visible for shrink_slab_memcg().
This is the moment shrink_slab_memcg() sees SHRINKER_REGISTERED.

> If so it seems easy to remove
> SHRINKER_REGISTERING.
> 
> We just need change that check to:
> !shrinker || !(shrinker->flags & SHRINKER_REGISTERED)
> 
>>>       up_write(&shrinker_rwsem);
>>>  }
>>>
>>> @@ -513,13 +514,17 @@ EXPORT_SYMBOL(register_shrinker);
>>>   */
>>>  void unregister_shrinker(struct shrinker *shrinker)
>>>  {
>>> -     if (!shrinker->nr_deferred)
>>> -             return;
>>> -     if (shrinker->flags & SHRINKER_MEMCG_AWARE)
>>> -             unregister_memcg_shrinker(shrinker);
>>>       down_write(&shrinker_rwsem);
>>
>> I do not think there are some users which registration may race with unregistration.
>> So, I think we should check SHRINKER_REGISTERED unlocked similar to we used to check
>> shrinker->nr_deferred unlocked.
> 
> Yes, I agree.
> 
>>
>>> +     if (!(shrinker->flags & SHRINKER_REGISTERED)) {
>>> +             up_write(&shrinker_rwsem);
>>> +             return;
>>> +     }
>>>       list_del(&shrinker->list);
>>> +     shrinker->flags &= ~SHRINKER_REGISTERED;
>>>       up_write(&shrinker_rwsem);
>>> +
>>> +     if (shrinker->flags & SHRINKER_MEMCG_AWARE)
>>> +             unregister_memcg_shrinker(shrinker);
>>>       kfree(shrinker->nr_deferred);
>>>       shrinker->nr_deferred = NULL;
>>>  }
>>>
>>
>>
Yang Shi Jan. 12, 2021, 8:58 p.m. UTC | #4
On Mon, Jan 11, 2021 at 1:38 PM Kirill Tkhai <ktkhai@virtuozzo.com> wrote:
>
> On 11.01.2021 21:17, Yang Shi wrote:
> > On Wed, Jan 6, 2021 at 2:22 AM Kirill Tkhai <ktkhai@virtuozzo.com> wrote:
> >>
> >> On 06.01.2021 01:58, Yang Shi wrote:
> >>> Currently registered shrinker is indicated by non-NULL shrinker->nr_deferred.
> >>> This approach is fine with nr_deferred at the shrinker level, but the following
> >>> patches will move MEMCG_AWARE shrinkers' nr_deferred to memcg level, so their
> >>> shrinker->nr_deferred would always be NULL.  This would prevent the shrinkers
> >>> from unregistering correctly.
> >>>
> >>> Signed-off-by: Yang Shi <shy828301@gmail.com>
> >>> ---
> >>>  include/linux/shrinker.h |  7 ++++---
> >>>  mm/vmscan.c              | 13 +++++++++----
> >>>  2 files changed, 13 insertions(+), 7 deletions(-)
> >>>
> >>> diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
> >>> index 0f80123650e2..1eac79ce57d4 100644
> >>> --- a/include/linux/shrinker.h
> >>> +++ b/include/linux/shrinker.h
> >>> @@ -79,13 +79,14 @@ struct shrinker {
> >>>  #define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
> >>>
> >>>  /* Flags */
> >>> -#define SHRINKER_NUMA_AWARE  (1 << 0)
> >>> -#define SHRINKER_MEMCG_AWARE (1 << 1)
> >>> +#define SHRINKER_REGISTERED  (1 << 0)
> >>> +#define SHRINKER_NUMA_AWARE  (1 << 1)
> >>> +#define SHRINKER_MEMCG_AWARE (1 << 2)
> >>>  /*
> >>>   * It just makes sense when the shrinker is also MEMCG_AWARE for now,
> >>>   * non-MEMCG_AWARE shrinker should not have this flag set.
> >>>   */
> >>> -#define SHRINKER_NONSLAB     (1 << 2)
> >>> +#define SHRINKER_NONSLAB     (1 << 3)
> >>>
> >>>  extern int prealloc_shrinker(struct shrinker *shrinker);
> >>>  extern void register_shrinker_prepared(struct shrinker *shrinker);
> >>> diff --git a/mm/vmscan.c b/mm/vmscan.c
> >>> index 8da765a85569..9761c7c27412 100644
> >>> --- a/mm/vmscan.c
> >>> +++ b/mm/vmscan.c
> >>> @@ -494,6 +494,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
> >>>       if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> >>>               idr_replace(&shrinker_idr, shrinker, shrinker->id);
> >>>  #endif
> >>> +     shrinker->flags |= SHRINKER_REGISTERED;
> >>
> >> In case of we introduce this new flag, we should kill old flag SHRINKER_REGISTERING,
> >> which are not needed anymore (we should you the new flag instead of that).
> >
> > The only think that I'm confused with is the check in
> > shrink_slab_memcg, it does:
> >
> > shrinker = idr_find(&shrinker_idr, i);
> > if (unlikely(!shrinker || shrinker == SHRINKER_REGISTERING)) {
> >
> > When allocating idr, the shrinker is associated with
> > SHRINKER_REGISTERING. But, shrink_slab_memcg does acquire read
> > shrinker_rwsem, and idr_alloc is called with holding write
> > shrinker_rwsem, so I'm supposed shrink_slab_memcg should never see
> > shrinker is registering.
>
> After prealloc_shrinker() shrinker is visible for shrink_slab_memcg().
> This is the moment shrink_slab_memcg() sees SHRINKER_REGISTERED.

Yes, this exactly is what I'm supposed.

>
> > If so it seems easy to remove
> > SHRINKER_REGISTERING.
> >
> > We just need change that check to:
> > !shrinker || !(shrinker->flags & SHRINKER_REGISTERED)
> >
> >>>       up_write(&shrinker_rwsem);
> >>>  }
> >>>
> >>> @@ -513,13 +514,17 @@ EXPORT_SYMBOL(register_shrinker);
> >>>   */
> >>>  void unregister_shrinker(struct shrinker *shrinker)
> >>>  {
> >>> -     if (!shrinker->nr_deferred)
> >>> -             return;
> >>> -     if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> >>> -             unregister_memcg_shrinker(shrinker);
> >>>       down_write(&shrinker_rwsem);
> >>
> >> I do not think there are some users which registration may race with unregistration.
> >> So, I think we should check SHRINKER_REGISTERED unlocked similar to we used to check
> >> shrinker->nr_deferred unlocked.
> >
> > Yes, I agree.
> >
> >>
> >>> +     if (!(shrinker->flags & SHRINKER_REGISTERED)) {
> >>> +             up_write(&shrinker_rwsem);
> >>> +             return;
> >>> +     }
> >>>       list_del(&shrinker->list);
> >>> +     shrinker->flags &= ~SHRINKER_REGISTERED;
> >>>       up_write(&shrinker_rwsem);
> >>> +
> >>> +     if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> >>> +             unregister_memcg_shrinker(shrinker);
> >>>       kfree(shrinker->nr_deferred);
> >>>       shrinker->nr_deferred = NULL;
> >>>  }
> >>>
> >>
> >>
>
>
diff mbox series

Patch

diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 0f80123650e2..1eac79ce57d4 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -79,13 +79,14 @@  struct shrinker {
 #define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
 
 /* Flags */
-#define SHRINKER_NUMA_AWARE	(1 << 0)
-#define SHRINKER_MEMCG_AWARE	(1 << 1)
+#define SHRINKER_REGISTERED	(1 << 0)
+#define SHRINKER_NUMA_AWARE	(1 << 1)
+#define SHRINKER_MEMCG_AWARE	(1 << 2)
 /*
  * It just makes sense when the shrinker is also MEMCG_AWARE for now,
  * non-MEMCG_AWARE shrinker should not have this flag set.
  */
-#define SHRINKER_NONSLAB	(1 << 2)
+#define SHRINKER_NONSLAB	(1 << 3)
 
 extern int prealloc_shrinker(struct shrinker *shrinker);
 extern void register_shrinker_prepared(struct shrinker *shrinker);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 8da765a85569..9761c7c27412 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -494,6 +494,7 @@  void register_shrinker_prepared(struct shrinker *shrinker)
 	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
 		idr_replace(&shrinker_idr, shrinker, shrinker->id);
 #endif
+	shrinker->flags |= SHRINKER_REGISTERED;
 	up_write(&shrinker_rwsem);
 }
 
@@ -513,13 +514,17 @@  EXPORT_SYMBOL(register_shrinker);
  */
 void unregister_shrinker(struct shrinker *shrinker)
 {
-	if (!shrinker->nr_deferred)
-		return;
-	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
-		unregister_memcg_shrinker(shrinker);
 	down_write(&shrinker_rwsem);
+	if (!(shrinker->flags & SHRINKER_REGISTERED)) {
+		up_write(&shrinker_rwsem);
+		return;
+	}
 	list_del(&shrinker->list);
+	shrinker->flags &= ~SHRINKER_REGISTERED;
 	up_write(&shrinker_rwsem);
+
+	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
+		unregister_memcg_shrinker(shrinker);
 	kfree(shrinker->nr_deferred);
 	shrinker->nr_deferred = NULL;
 }