Re: [PATCH 4/4] drm/i915: Invalidate our pages under memory pressure

[Jani Nikula <jani.nikula@linux.intel.com>]

On Wed, 16 Apr 2014, Robert Beckett <robert.beckett@intel.com> wrote:
> On 25/03/2014 13:23, Chris Wilson wrote:
>> Try to flush out dirty pages into the swapcache (and from there into the
>> swapfile) when under memory pressure and forced to drop GEM objects from
>> memory. In effect, this should just allow us to discard unused pages for
>> memory reclaim and to start writeback earlier.
>>
>> v2: Hugh Dickins warned that explicitly starting writeback from
>> shrink_slab was prone to deadlocks within shmemfs.
>>
>> Cc: Hugh Dickins <hughd@google.com>
>> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
>> ---
>>   drivers/gpu/drm/i915/i915_gem.c | 38 +++++++++++++++++++++++++++-----------
>>   1 file changed, 27 insertions(+), 11 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
>> index 135ee8bd55f6..8287fd6701c6 100644
>> --- a/drivers/gpu/drm/i915/i915_gem.c
>> +++ b/drivers/gpu/drm/i915/i915_gem.c
>> @@ -60,7 +60,6 @@ static unsigned long i915_gem_shrinker_scan(struct shrinker *shrinker,
>>   					    struct shrink_control *sc);
>>   static unsigned long i915_gem_purge(struct drm_i915_private *dev_priv, long target);
>>   static unsigned long i915_gem_shrink_all(struct drm_i915_private *dev_priv);
>> -static void i915_gem_object_truncate(struct drm_i915_gem_object *obj);
>>   static void i915_gem_retire_requests_ring(struct intel_ring_buffer *ring);
>>
>>   static bool cpu_cache_is_coherent(struct drm_device *dev,
>> @@ -1685,12 +1684,16 @@ i915_gem_mmap_gtt_ioctl(struct drm_device *dev, void *data,
>>   	return i915_gem_mmap_gtt(file, dev, args->handle, &args->offset);
>>   }
>>
>> +static inline int
>> +i915_gem_object_is_purgeable(struct drm_i915_gem_object *obj)
>> +{
>> +	return obj->madv == I915_MADV_DONTNEED;
>> +}
>> +
>>   /* Immediately discard the backing storage */
>>   static void
>>   i915_gem_object_truncate(struct drm_i915_gem_object *obj)
>>   {
>> -	struct inode *inode;
>> -
>>   	i915_gem_object_free_mmap_offset(obj);
>>
>>   	if (obj->base.filp == NULL)
>> @@ -1701,16 +1704,28 @@ i915_gem_object_truncate(struct drm_i915_gem_object *obj)
>>   	 * To do this we must instruct the shmfs to drop all of its
>>   	 * backing pages, *now*.
>>   	 */
>> -	inode = file_inode(obj->base.filp);
>> -	shmem_truncate_range(inode, 0, (loff_t)-1);
>> -
>> +	shmem_truncate_range(file_inode(obj->base.filp), 0, (loff_t)-1);
>>   	obj->madv = __I915_MADV_PURGED;
>>   }
>>
>> -static inline int
>> -i915_gem_object_is_purgeable(struct drm_i915_gem_object *obj)
>> +/* Try to discard unwanted pages */
>> +static void
>> +i915_gem_object_invalidate(struct drm_i915_gem_object *obj)
>>   {
>> -	return obj->madv == I915_MADV_DONTNEED;
>> +	struct address_space *mapping;
>> +
>> +	switch (obj->madv) {
>> +	case I915_MADV_DONTNEED:
>> +		i915_gem_object_truncate(obj);
>> +	case __I915_MADV_PURGED:
>> +		return;
>> +	}
>> +
>> +	if (obj->base.filp == NULL)
>> +		return;
>> +
>> +	mapping = file_inode(obj->base.filp)->i_mapping,
>> +	invalidate_mapping_pages(mapping, 0, (loff_t)-1);
>>   }
>>
>>   static void
>> @@ -1775,8 +1790,7 @@ i915_gem_object_put_pages(struct drm_i915_gem_object *obj)
>>   	ops->put_pages(obj);
>>   	obj->pages = NULL;
>>
>> -	if (i915_gem_object_is_purgeable(obj))
>> -		i915_gem_object_truncate(obj);
>> +	i915_gem_object_invalidate(obj);
>>
>>   	return 0;
>>   }
>> @@ -4201,6 +4215,8 @@ void i915_gem_free_object(struct drm_gem_object *gem_obj)
>>
>>   	if (WARN_ON(obj->pages_pin_count))
>>   		obj->pages_pin_count = 0;
>> +	if (obj->madv != __I915_MADV_PURGED)
>> +		obj->madv = I915_MADV_DONTNEED;
>>   	i915_gem_object_put_pages(obj);
>>   	i915_gem_object_free_mmap_offset(obj);
>>   	i915_gem_object_release_stolen(obj);
>>
>
> Functionally it looks good to me.
>
> Though, you may want a /* fall-through */ comment (some people cant 
> mentally parse fallthroughs without being prompted) and a default: 
> break; (to avoid any static code analysis complaints) in the switch in 
> i915_gem_object_invalidate.

Or just two if statements.

Jani.



>
> Reviewed-by: Robert Beckett <robert.beckett@intel.com>
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> Intel-gfx@lists.freedesktop.org
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-- 
Jani Nikula, Intel Open Source Technology Center