Re: [Freedreno] [PATCH v3 06/23] drm/msm/gem: Move locking in shrinker path

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On Fri, Oct 23, 2020 at 1:55 AM Kristian Høgsberg <hoegsberg@xxxxxxxxx> wrote:
>
> On Mon, Oct 19, 2020 at 10:45 PM Rob Clark <robdclark@xxxxxxxxx> wrote:
> >
> > From: Rob Clark <robdclark@xxxxxxxxxxxx>
> >
> > Move grabbing the bo lock into shrinker, with a msm_gem_trylock() to
> > skip over bo's that are already locked.  This gets rid of the nested
> > lock classes.
> >
> > Signed-off-by: Rob Clark <robdclark@xxxxxxxxxxxx>
> > ---
> >  drivers/gpu/drm/msm/msm_gem.c          | 24 +++++----------------
> >  drivers/gpu/drm/msm/msm_gem.h          | 29 ++++++++++----------------
> >  drivers/gpu/drm/msm/msm_gem_shrinker.c | 27 +++++++++++++++++-------
> >  3 files changed, 35 insertions(+), 45 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
> > index e0d8d739b068..1195847714ba 100644
> > --- a/drivers/gpu/drm/msm/msm_gem.c
> > +++ b/drivers/gpu/drm/msm/msm_gem.c
> > @@ -17,8 +17,6 @@
> >  #include "msm_gpu.h"
> >  #include "msm_mmu.h"
> >
> > -static void msm_gem_vunmap_locked(struct drm_gem_object *obj);
> > -
> >
> >  static dma_addr_t physaddr(struct drm_gem_object *obj)
> >  {
> > @@ -693,20 +691,19 @@ int msm_gem_madvise(struct drm_gem_object *obj, unsigned madv)
> >         return (madv != __MSM_MADV_PURGED);
> >  }
> >
> > -void msm_gem_purge(struct drm_gem_object *obj, enum msm_gem_lock subclass)
> > +void msm_gem_purge(struct drm_gem_object *obj)
> >  {
> >         struct drm_device *dev = obj->dev;
> >         struct msm_gem_object *msm_obj = to_msm_bo(obj);
> >
> >         WARN_ON(!mutex_is_locked(&dev->struct_mutex));
> > +       WARN_ON(!msm_gem_is_locked(obj));
> >         WARN_ON(!is_purgeable(msm_obj));
> >         WARN_ON(obj->import_attach);
> >
> > -       mutex_lock_nested(&msm_obj->lock, subclass);
> > -
> >         put_iova(obj);
> >
> > -       msm_gem_vunmap_locked(obj);
> > +       msm_gem_vunmap(obj);
> >
> >         put_pages(obj);
> >
> > @@ -724,11 +721,9 @@ void msm_gem_purge(struct drm_gem_object *obj, enum msm_gem_lock subclass)
> >
> >         invalidate_mapping_pages(file_inode(obj->filp)->i_mapping,
> >                         0, (loff_t)-1);
> > -
> > -       msm_gem_unlock(obj);
> >  }
> >
> > -static void msm_gem_vunmap_locked(struct drm_gem_object *obj)
> > +void msm_gem_vunmap(struct drm_gem_object *obj)
> >  {
> >         struct msm_gem_object *msm_obj = to_msm_bo(obj);
> >
> > @@ -741,15 +736,6 @@ static void msm_gem_vunmap_locked(struct drm_gem_object *obj)
> >         msm_obj->vaddr = NULL;
> >  }
> >
> > -void msm_gem_vunmap(struct drm_gem_object *obj, enum msm_gem_lock subclass)
> > -{
> > -       struct msm_gem_object *msm_obj = to_msm_bo(obj);
> > -
> > -       mutex_lock_nested(&msm_obj->lock, subclass);
> > -       msm_gem_vunmap_locked(obj);
> > -       msm_gem_unlock(obj);
> > -}
> > -
> >  /* must be called before _move_to_active().. */
> >  int msm_gem_sync_object(struct drm_gem_object *obj,
> >                 struct msm_fence_context *fctx, bool exclusive)
> > @@ -986,7 +972,7 @@ static void free_object(struct msm_gem_object *msm_obj)
> >
> >                 drm_prime_gem_destroy(obj, msm_obj->sgt);
> >         } else {
> > -               msm_gem_vunmap_locked(obj);
> > +               msm_gem_vunmap(obj);
> >                 put_pages(obj);
> >         }
> >
> > diff --git a/drivers/gpu/drm/msm/msm_gem.h b/drivers/gpu/drm/msm/msm_gem.h
> > index d55d5401a2d2..c5232b8da794 100644
> > --- a/drivers/gpu/drm/msm/msm_gem.h
> > +++ b/drivers/gpu/drm/msm/msm_gem.h
> > @@ -162,6 +162,13 @@ msm_gem_lock(struct drm_gem_object *obj)
> >         mutex_lock(&msm_obj->lock);
> >  }
> >
> > +static inline bool __must_check
> > +msm_gem_trylock(struct drm_gem_object *obj)
> > +{
> > +       struct msm_gem_object *msm_obj = to_msm_bo(obj);
> > +       return mutex_trylock_recursive(&msm_obj->lock) == MUTEX_TRYLOCK_SUCCESS;
>
> This can just be
>
>     return mutex_trylock(&msm_obj->lock) == 1;
>
> now, right?

yeah, I suppose.. although this is just transient and gets replaced in
a later patch

BR,
-R

> > +}
> > +
> >  static inline int
> >  msm_gem_lock_interruptible(struct drm_gem_object *obj)
> >  {
> > @@ -190,6 +197,7 @@ static inline bool is_active(struct msm_gem_object *msm_obj)
> >
> >  static inline bool is_purgeable(struct msm_gem_object *msm_obj)
> >  {
> > +       WARN_ON(!msm_gem_is_locked(&msm_obj->base));
> >         WARN_ON(!mutex_is_locked(&msm_obj->base.dev->struct_mutex));
> >         return (msm_obj->madv == MSM_MADV_DONTNEED) && msm_obj->sgt &&
> >                         !msm_obj->base.dma_buf && !msm_obj->base.import_attach;
> > @@ -197,27 +205,12 @@ static inline bool is_purgeable(struct msm_gem_object *msm_obj)
> >
> >  static inline bool is_vunmapable(struct msm_gem_object *msm_obj)
> >  {
> > +       WARN_ON(!msm_gem_is_locked(&msm_obj->base));
> >         return (msm_obj->vmap_count == 0) && msm_obj->vaddr;
> >  }
> >
> > -/* The shrinker can be triggered while we hold objA->lock, and need
> > - * to grab objB->lock to purge it.  Lockdep just sees these as a single
> > - * class of lock, so we use subclasses to teach it the difference.
> > - *
> > - * OBJ_LOCK_NORMAL is implicit (ie. normal mutex_lock() call), and
> > - * OBJ_LOCK_SHRINKER is used by shrinker.
> > - *
> > - * It is *essential* that we never go down paths that could trigger the
> > - * shrinker for a purgable object.  This is ensured by checking that
> > - * msm_obj->madv == MSM_MADV_WILLNEED.
> > - */
> > -enum msm_gem_lock {
> > -       OBJ_LOCK_NORMAL,
> > -       OBJ_LOCK_SHRINKER,
> > -};
> > -
> > -void msm_gem_purge(struct drm_gem_object *obj, enum msm_gem_lock subclass);
> > -void msm_gem_vunmap(struct drm_gem_object *obj, enum msm_gem_lock subclass);
> > +void msm_gem_purge(struct drm_gem_object *obj);
> > +void msm_gem_vunmap(struct drm_gem_object *obj);
> >  void msm_gem_free_work(struct work_struct *work);
> >
> >  /* Created per submit-ioctl, to track bo's and cmdstream bufs, etc,
> > diff --git a/drivers/gpu/drm/msm/msm_gem_shrinker.c b/drivers/gpu/drm/msm/msm_gem_shrinker.c
> > index 482576d7a39a..2dc0ffa925b4 100644
> > --- a/drivers/gpu/drm/msm/msm_gem_shrinker.c
> > +++ b/drivers/gpu/drm/msm/msm_gem_shrinker.c
> > @@ -52,8 +52,11 @@ msm_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
> >                 return 0;
> >
> >         list_for_each_entry(msm_obj, &priv->inactive_list, mm_list) {
> > +               if (!msm_gem_trylock(&msm_obj->base))
> > +                       continue;
> >                 if (is_purgeable(msm_obj))
> >                         count += msm_obj->base.size >> PAGE_SHIFT;
> > +               msm_gem_unlock(&msm_obj->base);
> >         }
> >
> >         if (unlock)
> > @@ -78,10 +81,13 @@ msm_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
> >         list_for_each_entry(msm_obj, &priv->inactive_list, mm_list) {
> >                 if (freed >= sc->nr_to_scan)
> >                         break;
> > +               if (!msm_gem_trylock(&msm_obj->base))
> > +                       continue;
> >                 if (is_purgeable(msm_obj)) {
> > -                       msm_gem_purge(&msm_obj->base, OBJ_LOCK_SHRINKER);
> > +                       msm_gem_purge(&msm_obj->base);
> >                         freed += msm_obj->base.size >> PAGE_SHIFT;
> >                 }
> > +               msm_gem_unlock(&msm_obj->base);
> >         }
> >
> >         if (unlock)
> > @@ -107,15 +113,20 @@ msm_gem_shrinker_vmap(struct notifier_block *nb, unsigned long event, void *ptr)
> >                 return NOTIFY_DONE;
> >
> >         list_for_each_entry(msm_obj, &priv->inactive_list, mm_list) {
> > +               if (!msm_gem_trylock(&msm_obj->base))
> > +                       continue;
> >                 if (is_vunmapable(msm_obj)) {
> > -                       msm_gem_vunmap(&msm_obj->base, OBJ_LOCK_SHRINKER);
> > -                       /* since we don't know any better, lets bail after a few
> > -                        * and if necessary the shrinker will be invoked again.
> > -                        * Seems better than unmapping *everything*
> > -                        */
> > -                       if (++unmapped >= 15)
> > -                               break;
> > +                       msm_gem_vunmap(&msm_obj->base);
> > +                       unmapped++;
> >                 }
> > +               msm_gem_unlock(&msm_obj->base);
> > +
> > +               /* since we don't know any better, lets bail after a few
> > +                * and if necessary the shrinker will be invoked again.
> > +                * Seems better than unmapping *everything*
> > +                */
> > +               if (++unmapped >= 15)
> > +                       break;
> >         }
> >
> >         if (unlock)
> > --
> > 2.26.2
> >
> > _______________________________________________
> > Freedreno mailing list
> > Freedreno@xxxxxxxxxxxxxxxxxxxxx
> > https://lists.freedesktop.org/mailman/listinfo/freedreno




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