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

[Jason Ekstrand <jason@jlekstrand.net>]

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.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

Feel free to land at-will and I'll deal with merge conflicts on my end.

> 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
>