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drm/i915/buddy: document the unused header bits

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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: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20210126103019.177622-1-matthew.auld@intel.com
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This commit is contained in:
Matthew Auld 2021-01-26 10:30:19 +00:00 committed by Daniel Vetter
parent b3f0c15a8e
commit a29a22917d
3 changed files with 56 additions and 2 deletions
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3
drivers/gpu/drm/i915/i915_buddy.c
View File

@ -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;
}

7
drivers/gpu/drm/i915/i915_buddy.h
View File

@ -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.

48
drivers/gpu/drm/i915/selftests/i915_buddy.c
View File

@ -727,6 +727,53 @@ err_fini:
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);