Commit a29a2291 authored by Matthew Auld's avatar Matthew Auld Committed by Daniel Vetter
Browse files

drm/i915/buddy: document the unused header bits 



The largest possible order is (63-PAGE_SHIFT), given that our min chunk
size is PAGE_SIZE. With that we should only need at most 6 bits to
represent all possible orders, giving us back 4 bits for other potential
uses.  Include a simple selftest to verify this.

Signed-off-by: default avatarMatthew Auld <matthew.auld@intel.com>
Reviewed-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20210126103019.177622-1-matthew.auld@intel.com


Signed-off-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
parent b3f0c15a

drivers/gpu/drm/i915/i915_buddy.c

+3 −0
Original line number Diff line number Diff line
@@ -48,6 +48,8 @@ static struct i915_buddy_block *i915_block_alloc(struct i915_buddy_block *parent 
{

	struct i915_buddy_block *block;



	GEM_BUG_ON(order > I915_BUDDY_MAX_ORDER);



	block = kmem_cache_zalloc(global.slab_blocks, GFP_KERNEL);

	if (!block)

		return NULL;
@@ -56,6 +58,7 @@ static struct i915_buddy_block *i915_block_alloc(struct i915_buddy_block *parent 
	block->header |= order;

	block->parent = parent;



	GEM_BUG_ON(block->header & I915_BUDDY_HEADER_UNUSED);

	return block;

}

drivers/gpu/drm/i915/i915_buddy.h

+5 −2
Original line number Diff line number Diff line
@@ -15,7 +15,9 @@ struct i915_buddy_block { 
#define   I915_BUDDY_ALLOCATED	   (1 << 10)

#define   I915_BUDDY_FREE	   (2 << 10)

#define   I915_BUDDY_SPLIT	   (3 << 10)

#define I915_BUDDY_HEADER_ORDER  GENMASK_ULL(9, 0)

/* Free to be used, if needed in the future */

#define I915_BUDDY_HEADER_UNUSED GENMASK_ULL(9, 6)

#define I915_BUDDY_HEADER_ORDER  GENMASK_ULL(5, 0)

	u64 header;



	struct i915_buddy_block *left;
@@ -34,7 +36,8 @@ struct i915_buddy_block { 
	struct list_head tmp_link;

};



#define I915_BUDDY_MAX_ORDER  I915_BUDDY_HEADER_ORDER

/* Order-zero must be at least PAGE_SIZE */

#define I915_BUDDY_MAX_ORDER (63 - PAGE_SHIFT)



/*

 * Binary Buddy System.

drivers/gpu/drm/i915/selftests/i915_buddy.c

+48 −0
Original line number Diff line number Diff line
@@ -727,6 +727,53 @@ static int igt_buddy_alloc_range(void *arg) 
	return err;

}



static int igt_buddy_alloc_limit(void *arg)

{

	struct i915_buddy_block *block;

	struct i915_buddy_mm mm;

	const u64 size = U64_MAX;

	int err;



	err = i915_buddy_init(&mm, size, PAGE_SIZE);

	if (err)

		return err;



	if (mm.max_order != I915_BUDDY_MAX_ORDER) {

		pr_err("mm.max_order(%d) != %d\n",

		       mm.max_order, I915_BUDDY_MAX_ORDER);

		err = -EINVAL;

		goto out_fini;

	}



	block = i915_buddy_alloc(&mm, mm.max_order);

	if (IS_ERR(block)) {

		err = PTR_ERR(block);

		goto out_fini;

	}



	if (i915_buddy_block_order(block) != mm.max_order) {

		pr_err("block order(%d) != %d\n",

		       i915_buddy_block_order(block), mm.max_order);

		err = -EINVAL;

		goto out_free;

	}



	if (i915_buddy_block_size(&mm, block) !=

	    BIT_ULL(mm.max_order) * PAGE_SIZE) {

		pr_err("block size(%llu) != %llu\n",

		       i915_buddy_block_size(&mm, block),

		       BIT_ULL(mm.max_order) * PAGE_SIZE);

		err = -EINVAL;

		goto out_free;

	}



out_free:

	i915_buddy_free(&mm, block);

out_fini:

	i915_buddy_fini(&mm);

	return err;

}



int i915_buddy_mock_selftests(void)

{

	static const struct i915_subtest tests[] = {
@@ -735,6 +782,7 @@ int i915_buddy_mock_selftests(void) 
		SUBTEST(igt_buddy_alloc_pathological),

		SUBTEST(igt_buddy_alloc_smoke),

		SUBTEST(igt_buddy_alloc_range),

		SUBTEST(igt_buddy_alloc_limit),

	};



	return i915_subtests(tests, NULL);