Re: [PATCH] drm/i915/ttm: consider all placements for the page alignment

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On 6/22/21 2:15 PM, Matthew Auld wrote:
On Tue, 22 Jun 2021 at 11:11, Thomas Hellström
<thomas.hellstrom@xxxxxxxxxxxxxxx> wrote:

On 6/22/21 11:58 AM, Matthew Auld wrote:
Just checking the current region is not enough, if we later migrate the
object somewhere else. For example if the placements are {SMEM, LMEM},
then we might get this wrong. Another idea might be to make the
page_alignment part of the ttm_place, instead of the BO.

Signed-off-by: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
---
   drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 21 ++++++++++++++++++++-
   1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
index c5deb8b7227c..5d894bba6430 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
@@ -753,6 +753,25 @@ void i915_ttm_bo_destroy(struct ttm_buffer_object *bo)
               call_rcu(&obj->rcu, __i915_gem_free_object_rcu);
   }

+static u64 i915_gem_object_page_size(struct drm_i915_gem_object *obj)
+{
+     u64 page_size;
+     int i;
+
+     if (!obj->mm.n_placements)
+             return obj->mm.region->min_page_size;
+
+     page_size = 0;
+     for (i = 0; i < obj->mm.n_placements; i++) {
+             struct intel_memory_region *mr = obj->mm.placements[i];
+
+             page_size = max_t(u64, mr->min_page_size, page_size);
+     }
+
+     GEM_BUG_ON(!page_size);
+     return page_size;
+}
+
   /**
    * __i915_gem_ttm_object_init - Initialize a ttm-backed i915 gem object
    * @mem: The initial memory region for the object.
@@ -793,7 +812,7 @@ int __i915_gem_ttm_object_init(struct intel_memory_region *mem,
       obj->base.vma_node.driver_private = i915_gem_to_ttm(obj);
       ret = ttm_bo_init(&i915->bdev, i915_gem_to_ttm(obj), size,
                         bo_type, &i915_sys_placement,
-                       mem->min_page_size >> PAGE_SHIFT,
+                       i915_gem_object_page_size(obj) >> PAGE_SHIFT,
Hmm, can't we just have the buddy manager silently enforce its
min_page_size?
Maybe, but we need some way of overriding it for all of our page-table
allocations(and some other stuff also), so being able to control the
page_alignment at the object level here seems reasonable? Could maybe
pass it through with create_lmem_with_page_size(..., page_size)? Ok,
it might be best to first type it and then see how it will all fit
together.

Hmm, OK, I'm not 100% sure what the various requirements are here on the object level. But for region requirements, I think we've historically enforced that through the manager, taking also the bo->page_alignment into account and applying the larger of the two,

There is an example in vmw_thp_insert_aligned().

/Thomas


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