diff mbox series

[v7,07/12] mm: vmscan: use a new flag to indicate shrinker is registered

Message ID 20210209174646.1310591-8-shy828301@gmail.com (mailing list archive)
State New
Headers show
Series [v7,01/12] mm: vmscan: use nid from shrink_control for tracepoint | expand

Commit Message

Yang Shi Feb. 9, 2021, 5:46 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.

Remove SHRINKER_REGISTERING since we could check if shrinker is registered
successfully by the new flag.

Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Yang Shi <shy828301@gmail.com>
---
 include/linux/shrinker.h |  7 ++++---
 mm/vmscan.c              | 31 +++++++++----------------------
 2 files changed, 13 insertions(+), 25 deletions(-)

Comments

Roman Gushchin Feb. 10, 2021, 12:39 a.m. UTC | #1
On Tue, Feb 09, 2021 at 09:46:41AM -0800, 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.
> 
> Remove SHRINKER_REGISTERING since we could check if shrinker is registered
> successfully by the new flag.
> 
> Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
> Signed-off-by: Yang Shi <shy828301@gmail.com>
> ---
>  include/linux/shrinker.h |  7 ++++---
>  mm/vmscan.c              | 31 +++++++++----------------------
>  2 files changed, 13 insertions(+), 25 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 273efbf4d53c..a047980536cf 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -315,19 +315,6 @@ void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
>  	}
>  }
>  
> -/*
> - * We allow subsystems to populate their shrinker-related
> - * LRU lists before register_shrinker_prepared() is called
> - * for the shrinker, since we don't want to impose
> - * restrictions on their internal registration order.
> - * In this case shrink_slab_memcg() may find corresponding
> - * bit is set in the shrinkers map.
> - *
> - * This value is used by the function to detect registering
> - * shrinkers and to skip do_shrink_slab() calls for them.
> - */
> -#define SHRINKER_REGISTERING ((struct shrinker *)~0UL)
> -
>  static DEFINE_IDR(shrinker_idr);
>  
>  static int prealloc_memcg_shrinker(struct shrinker *shrinker)
> @@ -336,7 +323,7 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker)
>  
>  	down_write(&shrinker_rwsem);
>  	/* This may call shrinker, so it must use down_read_trylock() */
> -	id = idr_alloc(&shrinker_idr, SHRINKER_REGISTERING, 0, 0, GFP_KERNEL);
> +	id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
>  	if (id < 0)
>  		goto unlock;
>  
> @@ -499,10 +486,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
>  {
>  	down_write(&shrinker_rwsem);
>  	list_add_tail(&shrinker->list, &shrinker_list);
> -#ifdef CONFIG_MEMCG
> -	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> -		idr_replace(&shrinker_idr, shrinker, shrinker->id);
> -#endif
> +	shrinker->flags |= SHRINKER_REGISTERED;
>  	up_write(&shrinker_rwsem);
>  }
>  
> @@ -522,13 +506,16 @@ EXPORT_SYMBOL(register_shrinker);
>   */
>  void unregister_shrinker(struct shrinker *shrinker)
>  {
> -	if (!shrinker->nr_deferred)
> +	if (!(shrinker->flags & SHRINKER_REGISTERED))
>  		return;
> -	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> -		unregister_memcg_shrinker(shrinker);
> +
>  	down_write(&shrinker_rwsem);
>  	list_del(&shrinker->list);
> +	shrinker->flags &= ~SHRINKER_REGISTERED;
>  	up_write(&shrinker_rwsem);
> +
> +	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> +		unregister_memcg_shrinker(shrinker);

Because unregister_memcg_shrinker() will take and release shrinker_rwsem once again,
I wonder if it's better to move it into the locked section and change the calling
convention to require the caller to take the semaphore?

>  	kfree(shrinkrem->nr_deferred);
>  	shrinker->nr_deferred = NULL;
>  }
> @@ -693,7 +680,7 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
>  		struct shrinker *shrinker;
>  
>  		shrinker = idr_find(&shrinker_idr, i);
> -		if (unlikely(!shrinker || shrinker == SHRINKER_REGISTERING)) {
> +		if (unlikely(!shrinker || !(shrinker->flags & SHRINKER_REGISTERED))) {
>  			if (!shrinker)
>  				clear_bit(i, info->map);
>  			continue;
> -- 
> 2.26.2
>
Yang Shi Feb. 10, 2021, 1:12 a.m. UTC | #2
On Tue, Feb 9, 2021 at 4:39 PM Roman Gushchin <guro@fb.com> wrote:
>
> On Tue, Feb 09, 2021 at 09:46:41AM -0800, 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.
> >
> > Remove SHRINKER_REGISTERING since we could check if shrinker is registered
> > successfully by the new flag.
> >
> > Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
> > Signed-off-by: Yang Shi <shy828301@gmail.com>
> > ---
> >  include/linux/shrinker.h |  7 ++++---
> >  mm/vmscan.c              | 31 +++++++++----------------------
> >  2 files changed, 13 insertions(+), 25 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 273efbf4d53c..a047980536cf 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -315,19 +315,6 @@ void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
> >       }
> >  }
> >
> > -/*
> > - * We allow subsystems to populate their shrinker-related
> > - * LRU lists before register_shrinker_prepared() is called
> > - * for the shrinker, since we don't want to impose
> > - * restrictions on their internal registration order.
> > - * In this case shrink_slab_memcg() may find corresponding
> > - * bit is set in the shrinkers map.
> > - *
> > - * This value is used by the function to detect registering
> > - * shrinkers and to skip do_shrink_slab() calls for them.
> > - */
> > -#define SHRINKER_REGISTERING ((struct shrinker *)~0UL)
> > -
> >  static DEFINE_IDR(shrinker_idr);
> >
> >  static int prealloc_memcg_shrinker(struct shrinker *shrinker)
> > @@ -336,7 +323,7 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker)
> >
> >       down_write(&shrinker_rwsem);
> >       /* This may call shrinker, so it must use down_read_trylock() */
> > -     id = idr_alloc(&shrinker_idr, SHRINKER_REGISTERING, 0, 0, GFP_KERNEL);
> > +     id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
> >       if (id < 0)
> >               goto unlock;
> >
> > @@ -499,10 +486,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
> >  {
> >       down_write(&shrinker_rwsem);
> >       list_add_tail(&shrinker->list, &shrinker_list);
> > -#ifdef CONFIG_MEMCG
> > -     if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> > -             idr_replace(&shrinker_idr, shrinker, shrinker->id);
> > -#endif
> > +     shrinker->flags |= SHRINKER_REGISTERED;
> >       up_write(&shrinker_rwsem);
> >  }
> >
> > @@ -522,13 +506,16 @@ EXPORT_SYMBOL(register_shrinker);
> >   */
> >  void unregister_shrinker(struct shrinker *shrinker)
> >  {
> > -     if (!shrinker->nr_deferred)
> > +     if (!(shrinker->flags & SHRINKER_REGISTERED))
> >               return;
> > -     if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> > -             unregister_memcg_shrinker(shrinker);
> > +
> >       down_write(&shrinker_rwsem);
> >       list_del(&shrinker->list);
> > +     shrinker->flags &= ~SHRINKER_REGISTERED;
> >       up_write(&shrinker_rwsem);
> > +
> > +     if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> > +             unregister_memcg_shrinker(shrinker);
>
> Because unregister_memcg_shrinker() will take and release shrinker_rwsem once again,
> I wonder if it's better to move it into the locked section and change the calling
> convention to require the caller to take the semaphore?

I don't think we could do that since unregister_memcg_shrinker() is
called by free_prealloced_shrinker() which is called without holding
the shrinker_rwsem by fs and workingset code.

We could add a bool parameter to indicate if the rwsem was acquired or
not, but IMHO it seems not worth it.

>
> >       kfree(shrinkrem->nr_deferred);
> >       shrinker->nr_deferred = NULL;
> >  }
> > @@ -693,7 +680,7 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
> >               struct shrinker *shrinker;
> >
> >               shrinker = idr_find(&shrinker_idr, i);
> > -             if (unlikely(!shrinker || shrinker == SHRINKER_REGISTERING)) {
> > +             if (unlikely(!shrinker || !(shrinker->flags & SHRINKER_REGISTERED))) {
> >                       if (!shrinker)
> >                               clear_bit(i, info->map);
> >                       continue;
> > --
> > 2.26.2
> >
Roman Gushchin Feb. 10, 2021, 1:34 a.m. UTC | #3
On Tue, Feb 09, 2021 at 05:12:51PM -0800, Yang Shi wrote:
> On Tue, Feb 9, 2021 at 4:39 PM Roman Gushchin <guro@fb.com> wrote:
> >
> > On Tue, Feb 09, 2021 at 09:46:41AM -0800, 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.
> > >
> > > Remove SHRINKER_REGISTERING since we could check if shrinker is registered
> > > successfully by the new flag.
> > >
> > > Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
> > > Signed-off-by: Yang Shi <shy828301@gmail.com>
> > > ---
> > >  include/linux/shrinker.h |  7 ++++---
> > >  mm/vmscan.c              | 31 +++++++++----------------------
> > >  2 files changed, 13 insertions(+), 25 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 273efbf4d53c..a047980536cf 100644
> > > --- a/mm/vmscan.c
> > > +++ b/mm/vmscan.c
> > > @@ -315,19 +315,6 @@ void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
> > >       }
> > >  }
> > >
> > > -/*
> > > - * We allow subsystems to populate their shrinker-related
> > > - * LRU lists before register_shrinker_prepared() is called
> > > - * for the shrinker, since we don't want to impose
> > > - * restrictions on their internal registration order.
> > > - * In this case shrink_slab_memcg() may find corresponding
> > > - * bit is set in the shrinkers map.
> > > - *
> > > - * This value is used by the function to detect registering
> > > - * shrinkers and to skip do_shrink_slab() calls for them.
> > > - */
> > > -#define SHRINKER_REGISTERING ((struct shrinker *)~0UL)
> > > -
> > >  static DEFINE_IDR(shrinker_idr);
> > >
> > >  static int prealloc_memcg_shrinker(struct shrinker *shrinker)
> > > @@ -336,7 +323,7 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker)
> > >
> > >       down_write(&shrinker_rwsem);
> > >       /* This may call shrinker, so it must use down_read_trylock() */
> > > -     id = idr_alloc(&shrinker_idr, SHRINKER_REGISTERING, 0, 0, GFP_KERNEL);
> > > +     id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
> > >       if (id < 0)
> > >               goto unlock;
> > >
> > > @@ -499,10 +486,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
> > >  {
> > >       down_write(&shrinker_rwsem);
> > >       list_add_tail(&shrinker->list, &shrinker_list);
> > > -#ifdef CONFIG_MEMCG
> > > -     if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> > > -             idr_replace(&shrinker_idr, shrinker, shrinker->id);
> > > -#endif
> > > +     shrinker->flags |= SHRINKER_REGISTERED;
> > >       up_write(&shrinker_rwsem);
> > >  }
> > >
> > > @@ -522,13 +506,16 @@ EXPORT_SYMBOL(register_shrinker);
> > >   */
> > >  void unregister_shrinker(struct shrinker *shrinker)
> > >  {
> > > -     if (!shrinker->nr_deferred)
> > > +     if (!(shrinker->flags & SHRINKER_REGISTERED))
> > >               return;
> > > -     if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> > > -             unregister_memcg_shrinker(shrinker);
> > > +
> > >       down_write(&shrinker_rwsem);
> > >       list_del(&shrinker->list);
> > > +     shrinker->flags &= ~SHRINKER_REGISTERED;
> > >       up_write(&shrinker_rwsem);
> > > +
> > > +     if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> > > +             unregister_memcg_shrinker(shrinker);
> >
> > Because unregister_memcg_shrinker() will take and release shrinker_rwsem once again,
> > I wonder if it's better to move it into the locked section and change the calling
> > convention to require the caller to take the semaphore?
> 
> I don't think we could do that since unregister_memcg_shrinker() is
> called by free_prealloced_shrinker() which is called without holding
> the shrinker_rwsem by fs and workingset code.
> 
> We could add a bool parameter to indicate if the rwsem was acquired or
> not, but IMHO it seems not worth it.

Can free_preallocated_shrinker() just do

if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
	down_write(&shrinker_rwsem);
	unregister_memcg_shrinker(shrinker);
	up_write(&shrinker_rwsem);
}

?
Yang Shi Feb. 10, 2021, 1:55 a.m. UTC | #4
On Tue, Feb 9, 2021 at 5:34 PM Roman Gushchin <guro@fb.com> wrote:
>
> On Tue, Feb 09, 2021 at 05:12:51PM -0800, Yang Shi wrote:
> > On Tue, Feb 9, 2021 at 4:39 PM Roman Gushchin <guro@fb.com> wrote:
> > >
> > > On Tue, Feb 09, 2021 at 09:46:41AM -0800, 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.
> > > >
> > > > Remove SHRINKER_REGISTERING since we could check if shrinker is registered
> > > > successfully by the new flag.
> > > >
> > > > Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
> > > > Signed-off-by: Yang Shi <shy828301@gmail.com>
> > > > ---
> > > >  include/linux/shrinker.h |  7 ++++---
> > > >  mm/vmscan.c              | 31 +++++++++----------------------
> > > >  2 files changed, 13 insertions(+), 25 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 273efbf4d53c..a047980536cf 100644
> > > > --- a/mm/vmscan.c
> > > > +++ b/mm/vmscan.c
> > > > @@ -315,19 +315,6 @@ void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
> > > >       }
> > > >  }
> > > >
> > > > -/*
> > > > - * We allow subsystems to populate their shrinker-related
> > > > - * LRU lists before register_shrinker_prepared() is called
> > > > - * for the shrinker, since we don't want to impose
> > > > - * restrictions on their internal registration order.
> > > > - * In this case shrink_slab_memcg() may find corresponding
> > > > - * bit is set in the shrinkers map.
> > > > - *
> > > > - * This value is used by the function to detect registering
> > > > - * shrinkers and to skip do_shrink_slab() calls for them.
> > > > - */
> > > > -#define SHRINKER_REGISTERING ((struct shrinker *)~0UL)
> > > > -
> > > >  static DEFINE_IDR(shrinker_idr);
> > > >
> > > >  static int prealloc_memcg_shrinker(struct shrinker *shrinker)
> > > > @@ -336,7 +323,7 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker)
> > > >
> > > >       down_write(&shrinker_rwsem);
> > > >       /* This may call shrinker, so it must use down_read_trylock() */
> > > > -     id = idr_alloc(&shrinker_idr, SHRINKER_REGISTERING, 0, 0, GFP_KERNEL);
> > > > +     id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
> > > >       if (id < 0)
> > > >               goto unlock;
> > > >
> > > > @@ -499,10 +486,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
> > > >  {
> > > >       down_write(&shrinker_rwsem);
> > > >       list_add_tail(&shrinker->list, &shrinker_list);
> > > > -#ifdef CONFIG_MEMCG
> > > > -     if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> > > > -             idr_replace(&shrinker_idr, shrinker, shrinker->id);
> > > > -#endif
> > > > +     shrinker->flags |= SHRINKER_REGISTERED;
> > > >       up_write(&shrinker_rwsem);
> > > >  }
> > > >
> > > > @@ -522,13 +506,16 @@ EXPORT_SYMBOL(register_shrinker);
> > > >   */
> > > >  void unregister_shrinker(struct shrinker *shrinker)
> > > >  {
> > > > -     if (!shrinker->nr_deferred)
> > > > +     if (!(shrinker->flags & SHRINKER_REGISTERED))
> > > >               return;
> > > > -     if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> > > > -             unregister_memcg_shrinker(shrinker);
> > > > +
> > > >       down_write(&shrinker_rwsem);
> > > >       list_del(&shrinker->list);
> > > > +     shrinker->flags &= ~SHRINKER_REGISTERED;
> > > >       up_write(&shrinker_rwsem);
> > > > +
> > > > +     if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> > > > +             unregister_memcg_shrinker(shrinker);
> > >
> > > Because unregister_memcg_shrinker() will take and release shrinker_rwsem once again,
> > > I wonder if it's better to move it into the locked section and change the calling
> > > convention to require the caller to take the semaphore?
> >
> > I don't think we could do that since unregister_memcg_shrinker() is
> > called by free_prealloced_shrinker() which is called without holding
> > the shrinker_rwsem by fs and workingset code.
> >
> > We could add a bool parameter to indicate if the rwsem was acquired or
> > not, but IMHO it seems not worth it.
>
> Can free_preallocated_shrinker() just do
>
> if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
>         down_write(&shrinker_rwsem);
>         unregister_memcg_shrinker(shrinker);
>         up_write(&shrinker_rwsem);
> }
>
> ?

Aha, yes. I didn't think of that way.
Vlastimil Babka Feb. 10, 2021, 6:23 p.m. UTC | #5
On 2/9/21 6:46 PM, 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.
> 
> Remove SHRINKER_REGISTERING since we could check if shrinker is registered
> successfully by the new flag.
> 
> Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
> Signed-off-by: Yang Shi <shy828301@gmail.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

With Roman's suggestion it's fine by me too.
Yang Shi Feb. 10, 2021, 6:45 p.m. UTC | #6
On Tue, Feb 9, 2021 at 4:39 PM Roman Gushchin <guro@fb.com> wrote:
>
> On Tue, Feb 09, 2021 at 09:46:41AM -0800, 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.
> >
> > Remove SHRINKER_REGISTERING since we could check if shrinker is registered
> > successfully by the new flag.
> >
> > Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
> > Signed-off-by: Yang Shi <shy828301@gmail.com>
> > ---
> >  include/linux/shrinker.h |  7 ++++---
> >  mm/vmscan.c              | 31 +++++++++----------------------
> >  2 files changed, 13 insertions(+), 25 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 273efbf4d53c..a047980536cf 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -315,19 +315,6 @@ void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
> >       }
> >  }
> >
> > -/*
> > - * We allow subsystems to populate their shrinker-related
> > - * LRU lists before register_shrinker_prepared() is called
> > - * for the shrinker, since we don't want to impose
> > - * restrictions on their internal registration order.
> > - * In this case shrink_slab_memcg() may find corresponding
> > - * bit is set in the shrinkers map.
> > - *
> > - * This value is used by the function to detect registering
> > - * shrinkers and to skip do_shrink_slab() calls for them.
> > - */
> > -#define SHRINKER_REGISTERING ((struct shrinker *)~0UL)
> > -
> >  static DEFINE_IDR(shrinker_idr);
> >
> >  static int prealloc_memcg_shrinker(struct shrinker *shrinker)
> > @@ -336,7 +323,7 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker)
> >
> >       down_write(&shrinker_rwsem);
> >       /* This may call shrinker, so it must use down_read_trylock() */
> > -     id = idr_alloc(&shrinker_idr, SHRINKER_REGISTERING, 0, 0, GFP_KERNEL);
> > +     id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
> >       if (id < 0)
> >               goto unlock;
> >
> > @@ -499,10 +486,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
> >  {
> >       down_write(&shrinker_rwsem);
> >       list_add_tail(&shrinker->list, &shrinker_list);
> > -#ifdef CONFIG_MEMCG
> > -     if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> > -             idr_replace(&shrinker_idr, shrinker, shrinker->id);
> > -#endif
> > +     shrinker->flags |= SHRINKER_REGISTERED;
> >       up_write(&shrinker_rwsem);
> >  }
> >
> > @@ -522,13 +506,16 @@ EXPORT_SYMBOL(register_shrinker);
> >   */
> >  void unregister_shrinker(struct shrinker *shrinker)
> >  {
> > -     if (!shrinker->nr_deferred)
> > +     if (!(shrinker->flags & SHRINKER_REGISTERED))
> >               return;
> > -     if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> > -             unregister_memcg_shrinker(shrinker);
> > +
> >       down_write(&shrinker_rwsem);
> >       list_del(&shrinker->list);
> > +     shrinker->flags &= ~SHRINKER_REGISTERED;
> >       up_write(&shrinker_rwsem);
> > +
> > +     if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> > +             unregister_memcg_shrinker(shrinker);
>
> Because unregister_memcg_shrinker() will take and release shrinker_rwsem once again,
> I wonder if it's better to move it into the locked section and change the calling
> convention to require the caller to take the semaphore?

BTW, I think lockdep_assert_held() in unregister_memcg_shrinker()
seems good enough.

>
> >       kfree(shrinkrem->nr_deferred);
> >       shrinker->nr_deferred = NULL;
> >  }
> > @@ -693,7 +680,7 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
> >               struct shrinker *shrinker;
> >
> >               shrinker = idr_find(&shrinker_idr, i);
> > -             if (unlikely(!shrinker || shrinker == SHRINKER_REGISTERING)) {
> > +             if (unlikely(!shrinker || !(shrinker->flags & SHRINKER_REGISTERED))) {
> >                       if (!shrinker)
> >                               clear_bit(i, info->map);
> >                       continue;
> > --
> > 2.26.2
> >
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 273efbf4d53c..a047980536cf 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -315,19 +315,6 @@  void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
 	}
 }
 
-/*
- * We allow subsystems to populate their shrinker-related
- * LRU lists before register_shrinker_prepared() is called
- * for the shrinker, since we don't want to impose
- * restrictions on their internal registration order.
- * In this case shrink_slab_memcg() may find corresponding
- * bit is set in the shrinkers map.
- *
- * This value is used by the function to detect registering
- * shrinkers and to skip do_shrink_slab() calls for them.
- */
-#define SHRINKER_REGISTERING ((struct shrinker *)~0UL)
-
 static DEFINE_IDR(shrinker_idr);
 
 static int prealloc_memcg_shrinker(struct shrinker *shrinker)
@@ -336,7 +323,7 @@  static int prealloc_memcg_shrinker(struct shrinker *shrinker)
 
 	down_write(&shrinker_rwsem);
 	/* This may call shrinker, so it must use down_read_trylock() */
-	id = idr_alloc(&shrinker_idr, SHRINKER_REGISTERING, 0, 0, GFP_KERNEL);
+	id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
 	if (id < 0)
 		goto unlock;
 
@@ -499,10 +486,7 @@  void register_shrinker_prepared(struct shrinker *shrinker)
 {
 	down_write(&shrinker_rwsem);
 	list_add_tail(&shrinker->list, &shrinker_list);
-#ifdef CONFIG_MEMCG
-	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
-		idr_replace(&shrinker_idr, shrinker, shrinker->id);
-#endif
+	shrinker->flags |= SHRINKER_REGISTERED;
 	up_write(&shrinker_rwsem);
 }
 
@@ -522,13 +506,16 @@  EXPORT_SYMBOL(register_shrinker);
  */
 void unregister_shrinker(struct shrinker *shrinker)
 {
-	if (!shrinker->nr_deferred)
+	if (!(shrinker->flags & SHRINKER_REGISTERED))
 		return;
-	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
-		unregister_memcg_shrinker(shrinker);
+
 	down_write(&shrinker_rwsem);
 	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;
 }
@@ -693,7 +680,7 @@  static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 		struct shrinker *shrinker;
 
 		shrinker = idr_find(&shrinker_idr, i);
-		if (unlikely(!shrinker || shrinker == SHRINKER_REGISTERING)) {
+		if (unlikely(!shrinker || !(shrinker->flags & SHRINKER_REGISTERED))) {
 			if (!shrinker)
 				clear_bit(i, info->map);
 			continue;