Re: [Intel-gfx] [PATCH] drm/i915: Ditch i915 globals shrink infrastructure

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Jul 21, 2021 at 10:24:01PM +0200, Daniel Vetter wrote:
> On Wed, Jul 21, 2021 at 10:17 PM Jason Ekstrand <jason@jlekstrand.net> wrote:
> >
> > On Wed, Jul 21, 2021 at 1:32 PM Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> > >
> > > This essentially reverts
> > >
> > > commit 84a1074920523430f9dc30ff907f4801b4820072
> > > Author: Chris Wilson <chris@chris-wilson.co.uk>
> > > Date:   Wed Jan 24 11:36:08 2018 +0000
> > >
> > >     drm/i915: Shrink the GEM kmem_caches upon idling
> > >
> > > mm/vmscan.c:do_shrink_slab() is a thing, if there's an issue with it
> > > then we need to fix that there, not hand-roll our own slab shrinking
> > > code in i915.
> > >
> > > Noticed while reviewing a patch set from Jason to fix up some issues
> > > in our i915_init() and i915_exit() module load/cleanup code. Now that
> > > i915_globals.c isn't any different than normal init/exit functions, we
> > > should convert them over to one unified table and remove
> > > i915_globals.[hc] entirely.
> >
> > Mind throwing in a comment somewhere about how i915 is one of only two
> > users of kmem_cache_shrink() in the entire kernel?  That also seems to
> > be pretty good evidence that it's not useful.
> 
> I missed one, there's also on in kunit (I think just got in, it's from
> this year at least per commit). That one seems actually legit, it's a
> selftest for some statistics around slabs I think, so has a legit
> reason to carefully control the state and trim anything that just
> hangs around.
> 
> I'll add something and push when CI approves.
> 
> > Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
> >
> > Feel free to land at-will and I'll deal with merge conflicts on my end.
> 
> I think if we can land this, then yours, then I type the conversion to
> explicit init/exit and we're done.

CI approved, merged as discussed. I'll look at your series now.
-Daniel

> > > Cc: David Airlie <airlied@linux.ie>
> > > Cc: Jason Ekstrand <jason@jlekstrand.net>
> > > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/gem/i915_gem_context.c |  6 --
> > >  drivers/gpu/drm/i915/gem/i915_gem_object.c  |  6 --
> > >  drivers/gpu/drm/i915/gt/intel_context.c     |  6 --
> > >  drivers/gpu/drm/i915/gt/intel_gt_pm.c       |  4 -
> > >  drivers/gpu/drm/i915/i915_active.c          |  6 --
> > >  drivers/gpu/drm/i915/i915_globals.c         | 95 ---------------------
> > >  drivers/gpu/drm/i915/i915_globals.h         |  3 -
> > >  drivers/gpu/drm/i915/i915_request.c         |  7 --
> > >  drivers/gpu/drm/i915/i915_scheduler.c       |  7 --
> > >  drivers/gpu/drm/i915/i915_vma.c             |  6 --
> > >  10 files changed, 146 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> > > index 7d6f52d8a801..bf2a2319353a 100644
> > > --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
> > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> > > @@ -2280,18 +2280,12 @@ i915_gem_engines_iter_next(struct i915_gem_engines_iter *it)
> > >  #include "selftests/i915_gem_context.c"
> > >  #endif
> > >
> > > -static void i915_global_gem_context_shrink(void)
> > > -{
> > > -       kmem_cache_shrink(global.slab_luts);
> > > -}
> > > -
> > >  static void i915_global_gem_context_exit(void)
> > >  {
> > >         kmem_cache_destroy(global.slab_luts);
> > >  }
> > >
> > >  static struct i915_global_gem_context global = { {
> > > -       .shrink = i915_global_gem_context_shrink,
> > >         .exit = i915_global_gem_context_exit,
> > >  } };
> > >
> > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i915/gem/i915_gem_object.c
> > > index 9da7b288b7ed..5c21cff33199 100644
> > > --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c
> > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c
> > > @@ -664,18 +664,12 @@ void i915_gem_init__objects(struct drm_i915_private *i915)
> > >         INIT_WORK(&i915->mm.free_work, __i915_gem_free_work);
> > >  }
> > >
> > > -static void i915_global_objects_shrink(void)
> > > -{
> > > -       kmem_cache_shrink(global.slab_objects);
> > > -}
> > > -
> > >  static void i915_global_objects_exit(void)
> > >  {
> > >         kmem_cache_destroy(global.slab_objects);
> > >  }
> > >
> > >  static struct i915_global_object global = { {
> > > -       .shrink = i915_global_objects_shrink,
> > >         .exit = i915_global_objects_exit,
> > >  } };
> > >
> > > diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
> > > index bd63813c8a80..c1338441cc1d 100644
> > > --- a/drivers/gpu/drm/i915/gt/intel_context.c
> > > +++ b/drivers/gpu/drm/i915/gt/intel_context.c
> > > @@ -398,18 +398,12 @@ void intel_context_fini(struct intel_context *ce)
> > >         i915_active_fini(&ce->active);
> > >  }
> > >
> > > -static void i915_global_context_shrink(void)
> > > -{
> > > -       kmem_cache_shrink(global.slab_ce);
> > > -}
> > > -
> > >  static void i915_global_context_exit(void)
> > >  {
> > >         kmem_cache_destroy(global.slab_ce);
> > >  }
> > >
> > >  static struct i915_global_context global = { {
> > > -       .shrink = i915_global_context_shrink,
> > >         .exit = i915_global_context_exit,
> > >  } };
> > >
> > > diff --git a/drivers/gpu/drm/i915/gt/intel_gt_pm.c b/drivers/gpu/drm/i915/gt/intel_gt_pm.c
> > > index aef3084e8b16..d86825437516 100644
> > > --- a/drivers/gpu/drm/i915/gt/intel_gt_pm.c
> > > +++ b/drivers/gpu/drm/i915/gt/intel_gt_pm.c
> > > @@ -67,8 +67,6 @@ static int __gt_unpark(struct intel_wakeref *wf)
> > >
> > >         GT_TRACE(gt, "\n");
> > >
> > > -       i915_globals_unpark();
> > > -
> > >         /*
> > >          * It seems that the DMC likes to transition between the DC states a lot
> > >          * when there are no connected displays (no active power domains) during
> > > @@ -116,8 +114,6 @@ static int __gt_park(struct intel_wakeref *wf)
> > >         GEM_BUG_ON(!wakeref);
> > >         intel_display_power_put_async(i915, POWER_DOMAIN_GT_IRQ, wakeref);
> > >
> > > -       i915_globals_park();
> > > -
> > >         return 0;
> > >  }
> > >
> > > diff --git a/drivers/gpu/drm/i915/i915_active.c b/drivers/gpu/drm/i915/i915_active.c
> > > index b1aa1c482c32..91723123ae9f 100644
> > > --- a/drivers/gpu/drm/i915/i915_active.c
> > > +++ b/drivers/gpu/drm/i915/i915_active.c
> > > @@ -1176,18 +1176,12 @@ struct i915_active *i915_active_create(void)
> > >  #include "selftests/i915_active.c"
> > >  #endif
> > >
> > > -static void i915_global_active_shrink(void)
> > > -{
> > > -       kmem_cache_shrink(global.slab_cache);
> > > -}
> > > -
> > >  static void i915_global_active_exit(void)
> > >  {
> > >         kmem_cache_destroy(global.slab_cache);
> > >  }
> > >
> > >  static struct i915_global_active global = { {
> > > -       .shrink = i915_global_active_shrink,
> > >         .exit = i915_global_active_exit,
> > >  } };
> > >
> > > diff --git a/drivers/gpu/drm/i915/i915_globals.c b/drivers/gpu/drm/i915/i915_globals.c
> > > index 77f1911c463b..7fe2e503897b 100644
> > > --- a/drivers/gpu/drm/i915/i915_globals.c
> > > +++ b/drivers/gpu/drm/i915/i915_globals.c
> > > @@ -17,61 +17,8 @@
> > >
> > >  static LIST_HEAD(globals);
> > >
> > > -static atomic_t active;
> > > -static atomic_t epoch;
> > > -static struct park_work {
> > > -       struct delayed_work work;
> > > -       struct rcu_head rcu;
> > > -       unsigned long flags;
> > > -#define PENDING 0
> > > -       int epoch;
> > > -} park;
> > > -
> > > -static void i915_globals_shrink(void)
> > > -{
> > > -       struct i915_global *global;
> > > -
> > > -       /*
> > > -        * kmem_cache_shrink() discards empty slabs and reorders partially
> > > -        * filled slabs to prioritise allocating from the mostly full slabs,
> > > -        * with the aim of reducing fragmentation.
> > > -        */
> > > -       list_for_each_entry(global, &globals, link)
> > > -               global->shrink();
> > > -}
> > > -
> > > -static void __i915_globals_grace(struct rcu_head *rcu)
> > > -{
> > > -       /* Ratelimit parking as shrinking is quite slow */
> > > -       schedule_delayed_work(&park.work, round_jiffies_up_relative(2 * HZ));
> > > -}
> > > -
> > > -static void __i915_globals_queue_rcu(void)
> > > -{
> > > -       park.epoch = atomic_inc_return(&epoch);
> > > -       if (!atomic_read(&active)) {
> > > -               init_rcu_head(&park.rcu);
> > > -               call_rcu(&park.rcu, __i915_globals_grace);
> > > -       }
> > > -}
> > > -
> > > -static void __i915_globals_park(struct work_struct *work)
> > > -{
> > > -       destroy_rcu_head(&park.rcu);
> > > -
> > > -       /* Confirm nothing woke up in the last grace period */
> > > -       if (park.epoch != atomic_read(&epoch)) {
> > > -               __i915_globals_queue_rcu();
> > > -               return;
> > > -       }
> > > -
> > > -       clear_bit(PENDING, &park.flags);
> > > -       i915_globals_shrink();
> > > -}
> > > -
> > >  void __init i915_global_register(struct i915_global *global)
> > >  {
> > > -       GEM_BUG_ON(!global->shrink);
> > >         GEM_BUG_ON(!global->exit);
> > >
> > >         list_add_tail(&global->link, &globals);
> > > @@ -109,52 +56,10 @@ int __init i915_globals_init(void)
> > >                 }
> > >         }
> > >
> > > -       INIT_DELAYED_WORK(&park.work, __i915_globals_park);
> > >         return 0;
> > >  }
> > >
> > > -void i915_globals_park(void)
> > > -{
> > > -       /*
> > > -        * Defer shrinking the global slab caches (and other work) until
> > > -        * after a RCU grace period has completed with no activity. This
> > > -        * is to try and reduce the latency impact on the consumers caused
> > > -        * by us shrinking the caches the same time as they are trying to
> > > -        * allocate, with the assumption being that if we idle long enough
> > > -        * for an RCU grace period to elapse since the last use, it is likely
> > > -        * to be longer until we need the caches again.
> > > -        */
> > > -       if (!atomic_dec_and_test(&active))
> > > -               return;
> > > -
> > > -       /* Queue cleanup after the next RCU grace period has freed slabs */
> > > -       if (!test_and_set_bit(PENDING, &park.flags))
> > > -               __i915_globals_queue_rcu();
> > > -}
> > > -
> > > -void i915_globals_unpark(void)
> > > -{
> > > -       atomic_inc(&epoch);
> > > -       atomic_inc(&active);
> > > -}
> > > -
> > > -static void __exit __i915_globals_flush(void)
> > > -{
> > > -       atomic_inc(&active); /* skip shrinking */
> > > -
> > > -       rcu_barrier(); /* wait for the work to be queued */
> > > -       flush_delayed_work(&park.work);
> > > -
> > > -       atomic_dec(&active);
> > > -}
> > > -
> > >  void __exit i915_globals_exit(void)
> > >  {
> > > -       GEM_BUG_ON(atomic_read(&active));
> > > -
> > > -       __i915_globals_flush();
> > >         __i915_globals_cleanup();
> > > -
> > > -       /* And ensure that our DESTROY_BY_RCU slabs are truly destroyed */
> > > -       rcu_barrier();
> > >  }
> > > diff --git a/drivers/gpu/drm/i915/i915_globals.h b/drivers/gpu/drm/i915/i915_globals.h
> > > index 2d199f411a4a..9e6b4fd07528 100644
> > > --- a/drivers/gpu/drm/i915/i915_globals.h
> > > +++ b/drivers/gpu/drm/i915/i915_globals.h
> > > @@ -14,15 +14,12 @@ typedef void (*i915_global_func_t)(void);
> > >  struct i915_global {
> > >         struct list_head link;
> > >
> > > -       i915_global_func_t shrink;
> > >         i915_global_func_t exit;
> > >  };
> > >
> > >  void i915_global_register(struct i915_global *global);
> > >
> > >  int i915_globals_init(void);
> > > -void i915_globals_park(void);
> > > -void i915_globals_unpark(void);
> > >  void i915_globals_exit(void);
> > >
> > >  /* constructors */
> > > diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> > > index 09ebea9a0090..d3de9f60e03a 100644
> > > --- a/drivers/gpu/drm/i915/i915_request.c
> > > +++ b/drivers/gpu/drm/i915/i915_request.c
> > > @@ -2077,12 +2077,6 @@ void i915_request_show(struct drm_printer *m,
> > >  #include "selftests/i915_request.c"
> > >  #endif
> > >
> > > -static void i915_global_request_shrink(void)
> > > -{
> > > -       kmem_cache_shrink(global.slab_execute_cbs);
> > > -       kmem_cache_shrink(global.slab_requests);
> > > -}
> > > -
> > >  static void i915_global_request_exit(void)
> > >  {
> > >         kmem_cache_destroy(global.slab_execute_cbs);
> > > @@ -2090,7 +2084,6 @@ static void i915_global_request_exit(void)
> > >  }
> > >
> > >  static struct i915_global_request global = { {
> > > -       .shrink = i915_global_request_shrink,
> > >         .exit = i915_global_request_exit,
> > >  } };
> > >
> > > diff --git a/drivers/gpu/drm/i915/i915_scheduler.c b/drivers/gpu/drm/i915/i915_scheduler.c
> > > index 3a58a9130309..561c649e59f7 100644
> > > --- a/drivers/gpu/drm/i915/i915_scheduler.c
> > > +++ b/drivers/gpu/drm/i915/i915_scheduler.c
> > > @@ -475,12 +475,6 @@ i915_sched_engine_create(unsigned int subclass)
> > >         return sched_engine;
> > >  }
> > >
> > > -static void i915_global_scheduler_shrink(void)
> > > -{
> > > -       kmem_cache_shrink(global.slab_dependencies);
> > > -       kmem_cache_shrink(global.slab_priorities);
> > > -}
> > > -
> > >  static void i915_global_scheduler_exit(void)
> > >  {
> > >         kmem_cache_destroy(global.slab_dependencies);
> > > @@ -488,7 +482,6 @@ static void i915_global_scheduler_exit(void)
> > >  }
> > >
> > >  static struct i915_global_scheduler global = { {
> > > -       .shrink = i915_global_scheduler_shrink,
> > >         .exit = i915_global_scheduler_exit,
> > >  } };
> > >
> > > diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
> > > index 5b9dce0f443b..09a7c47926f7 100644
> > > --- a/drivers/gpu/drm/i915/i915_vma.c
> > > +++ b/drivers/gpu/drm/i915/i915_vma.c
> > > @@ -1414,18 +1414,12 @@ void i915_vma_make_purgeable(struct i915_vma *vma)
> > >  #include "selftests/i915_vma.c"
> > >  #endif
> > >
> > > -static void i915_global_vma_shrink(void)
> > > -{
> > > -       kmem_cache_shrink(global.slab_vmas);
> > > -}
> > > -
> > >  static void i915_global_vma_exit(void)
> > >  {
> > >         kmem_cache_destroy(global.slab_vmas);
> > >  }
> > >
> > >  static struct i915_global_vma global = { {
> > > -       .shrink = i915_global_vma_shrink,
> > >         .exit = i915_global_vma_exit,
> > >  } };
> > >
> > > --
> > > 2.32.0
> > >
> 
> 
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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