Re: [PATCH 03/10] drm/ttm: do not check if list is empty in ttm_bo_force_list_clean

[Maarten Lankhorst <maarten.lankhorst@canonical.com>]

Op 19-11-12 14:33, Thomas Hellstrom schreef:
> On 11/12/2012 03:00 PM, Maarten Lankhorst wrote:
>> Just use the return error from ttm_mem_evict_first instead.
>
> Here driver need to be able to evict a memory type completely, because they might shut down
> the memory type or clear it for some legacy usage, suspending or whatever, so returning 0 on -EBUSY isn't sufficient,
> we need at least a list empty check, and a shared reservation at this point is illegal.
>
> This is a point where the mechanism to exclude other reservers is needed, as we discussed previously.
> vmwgfx is using the ttm lock, but will of course adapt if a new mechanism is emerging.
Normally ttm_mem_evict_first only returns -EBUSY if the list is empty and no_wait = false,
so I thought using the return code would be equivalent.

We could do spin_lock(&glob->lru_lock); WARN_ON(!list_empty(&man->lru_lock)); spin_unlock(&glob->lru_lock); to handle this after -EBUSY.

With a lot of objects on the lru list, this would save taking lru_lock twice for each object.

~Maarten