Re: [PATCH 2/2] drm/i915: Make pages of GFX allocations movable

["Goel, Akash" <akash.goel@intel.com>]

On 3/23/2016 1:28 PM, Chris Wilson wrote:
> On Wed, Mar 23, 2016 at 11:39:44AM +0530, akash.goel@intel.com wrote:
>> +#ifdef CONFIG_MIGRATION
>> +static int i915_migratepage(struct address_space *mapping,
>> +			    struct page *newpage, struct page *page,
>> +			    enum migrate_mode mode, void *dev_priv_data)
>
> If we move this to i915_gem_shrink_migratepage (i.e. i915_gem_shrink),
> we can
>
>> +	/*
>> +	 * Use trylock here, with a timeout, for struct_mutex as
>> +	 * otherwise there is a possibility of deadlock due to lock
>> +	 * inversion. This path, which tries to migrate a particular
>> +	 * page after locking that page, can race with a path which
>> +	 * truncate/purge pages of the corresponding object (after
>> +	 * acquiring struct_mutex). Since page truncation will also
>> +	 * try to lock the page, a scenario of deadlock can arise.
>> +	 */
>> +	while (!mutex_trylock(&dev->struct_mutex) && --timeout)
>> +		schedule_timeout_killable(1);
>
> replace this with i915_gem_shrinker_lock() and like constructs with the
> other shrinkers.

fine, will rename the function to gem_shrink_migratepage, move it inside 
the gem_shrinker.c file, and use the existing constructs.

 > Any reason for dropping the early
 > if (!page_private(obj)) skip?
 >

Would this sequence be fine ?

	if (!page_private(page))
		goto migrate; /*skip */

	Loop for locking mutex

	obj = (struct drm_i915_gem_object *)page_private(page);

	if (!PageSwapCache(page) && obj) {


> Similarly there are other patterns here that would benefit from
> integration with existing shrinker logic. However, things like tidying
> up the pin_display, unbinding, rpm lock inversion are still only on
> list.

Tidying, like split that one single if condition into multiple if, else 
if blocks ?

Best regards
Akash
> -Chris
>

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