Re: [PATCH v2 1/2] drm/buddy: Add kernel-doc for allocator structures and flags

["Yadav, Sanjay Kumar" <sanjay.kumar.yadav@intel.com>]

On 12-02-2026 13:10, Arunpravin Paneer Selvam wrote:
>
>
> On 2/12/2026 1:08 PM, Arunpravin Paneer Selvam wrote:
>>
>>
>> On 2/11/2026 11:01 AM, Sanjay Yadav wrote:
>>> Add missing kernel-doc for GPU buddy allocator flags,
>>> gpu_buddy_block, and gpu_buddy. The documentation covers block
>>> header fields, allocator roots, free trees, and allocation flags
>>> such as RANGE, TOPDOWN, CONTIGUOUS, CLEAR, and TRIM_DISABLE.
>>> Private members are marked with kernel-doc private markers
>>> and documented with regular comments.
>>>
>>> No functional changes.
>>>
>>> v2:
>>> - Corrected GPU_BUDDY_CLEAR_TREE and GPU_BUDDY_DIRTY_TREE index 
>>> values (Arun)
>>> - Rebased after DRM buddy allocator moved to drivers/gpu/
>>> - Updated commit message
>>>
>>> Cc: Christian König<christian.koenig@amd.com>
>>> Cc: Arunpravin Paneer Selvam<Arunpravin.PaneerSelvam@amd.com>
>>> Suggested-by: Matthew Auld<matthew.auld@intel.com>
>>> Signed-off-by: Sanjay Yadav<sanjay.kumar.yadav@intel.com>
>>> ---
>>>   include/linux/gpu_buddy.h | 122 
>>> +++++++++++++++++++++++++++++++-------
>>>   1 file changed, 102 insertions(+), 20 deletions(-)
>>>
>>> diff --git a/include/linux/gpu_buddy.h b/include/linux/gpu_buddy.h
>>> index 07ac65db6d2e..b06241c78437 100644
>>> --- a/include/linux/gpu_buddy.h
>>> +++ b/include/linux/gpu_buddy.h
>>> @@ -12,11 +12,58 @@
>>>   #include <linux/sched.h>
>>>   #include <linux/rbtree.h>
>>>   +/**
>>> + * GPU_BUDDY_RANGE_ALLOCATION - Allocate within a specific address 
>>> range
>>> + *
>>> + * When set, allocation is restricted to the range [start, end) 
>>> specified
>>> + * in gpu_buddy_alloc_blocks(). Without this flag, start/end are 
>>> ignored
>>> + * and allocation can use any free space.
>>> + */
>>>   #define GPU_BUDDY_RANGE_ALLOCATION        BIT(0)
>>> +
>>> +/**
>>> + * GPU_BUDDY_TOPDOWN_ALLOCATION - Allocate from top of address space
>>> + *
>>> + * Allocate starting from high addresses and working down. Useful for
>>> + * separating different allocation types (e.g., kernel vs userspace)
>>> + * to reduce fragmentation.
>>> + */
>>>   #define GPU_BUDDY_TOPDOWN_ALLOCATION        BIT(1)
>>> +
>>> +/**
>>> + * GPU_BUDDY_CONTIGUOUS_ALLOCATION - Require physically contiguous 
>>> blocks
>>> + *
>>> + * The allocation must be satisfied with a single contiguous block.
>>> + * If the requested size cannot be allocated contiguously, the
>>> + * allocation fails with -ENOSPC.
>>> + */
>>>   #define GPU_BUDDY_CONTIGUOUS_ALLOCATION        BIT(2)
>>> +
>>> +/**
>>> + * GPU_BUDDY_CLEAR_ALLOCATION - Prefer pre-cleared (zeroed) memory
>>> + *
>>> + * Attempt to allocate from the clear tree first. If insufficient 
>>> clear
>>> + * memory is available, falls back to dirty memory. Useful when the
>>> + * caller needs zeroed memory and wants to avoid GPU clear operations.
>>> + */
>>>   #define GPU_BUDDY_CLEAR_ALLOCATION        BIT(3)
>>> +
>>> +/**
>>> + * GPU_BUDDY_CLEARED - Mark returned blocks as cleared
>>> + *
>>> + * Used with gpu_buddy_free_list() to indicate that the memory being
>>> + * freed has been cleared (zeroed). The blocks will be placed in the
>>> + * clear tree for future GPU_BUDDY_CLEAR_ALLOCATION requests.
>>> + */
>>>   #define GPU_BUDDY_CLEARED            BIT(4)
>>> +
>>> +/**
>>> + * GPU_BUDDY_TRIM_DISABLE - Disable automatic block trimming
>>> + *
>>> + * By default, if an allocation is smaller than the allocated block,
>>> + * excess memory is trimmed and returned to the free pool. This flag
>>> + * disables trimming, keeping the full power-of-two block size.
>>> + */
>>>   #define GPU_BUDDY_TRIM_DISABLE            BIT(5)
>>>     enum gpu_buddy_free_tree {
>>> @@ -28,7 +75,27 @@ enum gpu_buddy_free_tree {
>>>   #define for_each_free_tree(tree) \
>>>       for ((tree) = 0; (tree) < GPU_BUDDY_MAX_FREE_TREES; (tree)++)
>>>   +/**
>>> + * struct gpu_buddy_block - Block within a buddy allocator
>>> + *
>>> + * Each block in the buddy allocator is represented by this structure.
>>> + * Blocks are organized in a binary tree where each parent block 
>>> can be
>>> + * split into two children (left and right buddies). The allocator 
>>> manages
>>> + * blocks at various orders (power-of-2 sizes) from chunk_size up 
>>> to the
>>> + * largest contiguous region.
>>> + *
>>> + * @private: Private data owned by the allocator user (e.g., 
>>> driver-specific data)
>>> + * @link: List node for user ownership while block is allocated
>>> + */
>>>   struct gpu_buddy_block {
>>> +/* private: */
>>> +    /*
>>> +     * Header bit layout:
>>> +     * - Bits 63:12: block offset within the address space
>>> +     * - Bits 11:10: state (ALLOCATED, FREE, or SPLIT)
>>> +     * - Bit 9: clear bit (1 if memory is zeroed)
>> I think we should add
>> - Bits 8:9: reserved
> it should be -Bits 8:6: reserved
>>
>> Apart from that, looks good to me.
>> Reviewed-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Thanks Arun for your prompt review, helpful comments, and your time.
>>> +     * - Bits 5:0: order (log2 of size relative to chunk_size)
>>> +     */
>>>   #define GPU_BUDDY_HEADER_OFFSET GENMASK_ULL(63, 12)
>>>   #define GPU_BUDDY_HEADER_STATE  GENMASK_ULL(11, 10)
>>>   #define   GPU_BUDDY_ALLOCATED       (1 << 10)
>>> @@ -43,7 +110,7 @@ struct gpu_buddy_block {
>>>       struct gpu_buddy_block *left;
>>>       struct gpu_buddy_block *right;
>>>       struct gpu_buddy_block *parent;
>>> -
>>> +/* public: */
>>>       void *private; /* owned by creator */
>>>         /*
>>> @@ -53,43 +120,58 @@ struct gpu_buddy_block {
>>>        * gpu_buddy_free* ownership is given back to the mm.
>>>        */
>>>       union {
>>> +/* private: */
>>>           struct rb_node rb;
>>> +/* public: */
>>>           struct list_head link;
>>>       };
>>> -
>>> +/* private: */
>>>       struct list_head tmp_link;
>>>   };
>>>     /* Order-zero must be at least SZ_4K */
>>>   #define GPU_BUDDY_MAX_ORDER (63 - 12)
>>>   -/*
>>> - * Binary Buddy System.
>>> +/**
>>> + * struct gpu_buddy - GPU binary buddy allocator
>>> + *
>>> + * The buddy allocator provides efficient power-of-two memory 
>>> allocation
>>> + * with fast allocation and free operations. It is commonly used 
>>> for GPU
>>> + * memory management where allocations can be split into power-of-two
>>> + * block sizes.
>>>    *
>>> - * Locking should be handled by the user, a simple mutex around
>>> - * gpu_buddy_alloc* and gpu_buddy_free* should suffice.
>>> + * Locking should be handled by the user; a simple mutex around
>>> + * gpu_buddy_alloc_blocks() and 
>>> gpu_buddy_free_block()/gpu_buddy_free_list()
>>> + * should suffice.
>>> + *
>>> + * @n_roots: Number of root blocks in the roots array.
>>> + * @max_order: Maximum block order (log2 of largest block size / 
>>> chunk_size).
>>> + * @chunk_size: Minimum allocation granularity in bytes. Must be at 
>>> least SZ_4K.
>>> + * @size: Total size of the address space managed by this allocator 
>>> in bytes.
>>> + * @avail: Total free space currently available for allocation in 
>>> bytes.
>>> + * @clear_avail: Free space available in the clear tree (zeroed 
>>> memory) in bytes.
>>> + *               This is a subset of @avail.
>>>    */
>>>   struct gpu_buddy {
>>> -    /* Maintain a free list for each order. */
>>> -    struct rb_root **free_trees;
>>> -
>>> +/* private: */
>>>       /*
>>> -     * Maintain explicit binary tree(s) to track the allocation of the
>>> -     * address space. This gives us a simple way of finding a buddy 
>>> block
>>> -     * and performing the potentially recursive merge step when 
>>> freeing a
>>> -     * block.  Nodes are either allocated or free, in which case 
>>> they will
>>> -     * also exist on the respective free list.
>>> +     * Array of red-black trees for free block management.
>>> +     * Indexed as free_trees[clear/dirty][order] where:
>>> +     * - Index 0 (GPU_BUDDY_CLEAR_TREE): blocks with zeroed content
>>> +     * - Index 1 (GPU_BUDDY_DIRTY_TREE): blocks with unknown content
>>> +     * Each tree holds free blocks of the corresponding order.
>>>        */
>>> -    struct gpu_buddy_block **roots;
>>> -
>>> +    struct rb_root **free_trees;
>>>       /*
>>> -     * Anything from here is public, and remains static for the 
>>> lifetime of
>>> -     * the mm. Everything above is considered do-not-touch.
>>> +     * Array of root blocks representing the top-level blocks of the
>>> +     * binary tree(s). Multiple roots exist when the total size is not
>>> +     * a power of two, with each root being the largest power-of-two
>>> +     * that fits in the remaining space.
>>>        */
>>> +    struct gpu_buddy_block **roots;
>>> +/* public: */
>>>       unsigned int n_roots;
>>>       unsigned int max_order;
>>> -
>>> -    /* Must be at least SZ_4K */
>>>       u64 chunk_size;
>>>       u64 size;
>>>       u64 avail;
>>
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