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

Rob Clark
2020-10-23T14:48:36Z

On Fri, Oct 23, 2020 at 1:55 AM Kristian Høgsberg <hoegsberg@gmail.com> wrote:
>
> On Mon, Oct 19, 2020 at 10:45 PM Rob Clark <robdclark@gmail.com> wrote:
> >
> > From: Rob Clark <robdclark@chromium.org>
> >
> > 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@chromium.org>
> > ---
> > 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
> >
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