Re: [PATCH v2] gpu/buddy: bail out of try_harder when alignment cannot be honoured

[Arunpravin Paneer Selvam <arunpravin.paneerselvam@amd.com>]

On 7/3/2026 6:05 AM, John Olender wrote:
> On 7/2/26 6:48 AM, Matthew Auld wrote:
>> On 29/06/2026 08:43, Arunpravin Paneer Selvam wrote:
>>> The try_harder contiguous fallback could return a range whose start
>>> offset did not match the caller's min_block_size. When a candidate's
>>> start is misaligned, realign it: free the misaligned run and reallocate
>>> exactly @size at the next lower min_block_size boundary. This keeps the
>>> returned size unchanged with no surplus to trim, and rejects the request
>>> only when no aligned candidate fits.
>>>
>>> v2: align misaligned candidates down to min_block_size instead of
>>>       bailing out, for both the RHS and LHS paths (Matthew).
>>>
>>> Suggested-by: Christian König <christian.koenig@amd.com>
>>> Fixes: 0a1844bf0b53 ("drm/buddy: Improve contiguous memory allocation")
>>> Cc: Matthew Auld <matthew.auld@intel.com>
>>> Cc: Christian König <christian.koenig@amd.com>
>>> Cc: Timur Kristóf <timur.kristof@gmail.com>
>>> Cc: John Olender <john.olender@gmail.com>
>>> Cc: stable@vger.kernel.org
>>> Signed-off-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
>> Reviewed-by: Matthew Auld <matthew.auld@intel.com>
>>
> I haven't hit any issues with this revision during testing.
Thanks for testing.

Regards,
Arun.
>
> Thanks,
> John
>
>>> ---
>>>    drivers/gpu/buddy.c | 63 +++++++++++++++++++++++++++++++--------------
>>>    1 file changed, 44 insertions(+), 19 deletions(-)
>>>
>>> diff --git a/drivers/gpu/buddy.c b/drivers/gpu/buddy.c
>>> index dc81fe0301ce..3c73ae87f3c5 100644
>>> --- a/drivers/gpu/buddy.c
>>> +++ b/drivers/gpu/buddy.c
>>> @@ -1118,22 +1118,30 @@ static int __gpu_buddy_alloc_range(struct gpu_buddy *mm,
>>>                     blocks, total_allocated_on_err);
>>>    }
>>>    +static int __alloc_contig_aligned_retry(struct gpu_buddy *mm,
>>> +                    u64 unaligned_offset,
>>> +                    u64 size,
>>> +                    u64 min_block_size,
>>> +                    struct list_head *blocks)
>>> +{
>>> +    u64 aligned_offset = round_down(unaligned_offset, min_block_size);
>>> +
>>> +    return __gpu_buddy_alloc_range(mm, aligned_offset, size, NULL, blocks);
>>> +}
>>> +
>>>    static int __alloc_contig_try_harder(struct gpu_buddy *mm,
>>>                         u64 size,
>>>                         u64 min_block_size,
>>>                         struct list_head *blocks)
>>>    {
>>> -    u64 rhs_offset, lhs_offset, lhs_size, filled;
>>> +    u64 rhs_offset, lhs_offset, filled;
>>>        struct gpu_buddy_block *block;
>>>        unsigned int tree, order;
>>> -    LIST_HEAD(blocks_lhs);
>>> -    unsigned long pages;
>>>        u64 modify_size;
>>>        int err;
>>>          modify_size = rounddown_pow_of_two(size);
>>> -    pages = modify_size >> ilog2(mm->chunk_size);
>>> -    order = fls(pages) - 1;
>>> +    order = ilog2(modify_size) - ilog2(mm->chunk_size);
>>>        if (order == 0)
>>>            return -ENOSPC;
>>>    @@ -1149,31 +1157,48 @@ static int __alloc_contig_try_harder(struct gpu_buddy *mm,
>>>            while (iter) {
>>>                block = rbtree_get_free_block(iter);
>>>    -            /* Allocate blocks traversing RHS */
>>>                rhs_offset = gpu_buddy_block_offset(block);
>>> +
>>> +            /* Allocate blocks traversing RHS */
>>>                err =  __gpu_buddy_alloc_range(mm, rhs_offset, size,
>>>                                   &filled, blocks);
>>> -            if (!err || err != -ENOSPC)
>>> +            if (err && err != -ENOSPC)
>>>                    return err;
>>> +            if (!err && IS_ALIGNED(rhs_offset, min_block_size))
>>> +                return 0;
>>> +            if (!err) {
>>> +                /* Allocate the unaligned RHS offset using round_down */
>>> +                gpu_buddy_free_list_internal(mm, blocks);
>>> +                err = __alloc_contig_aligned_retry(mm, rhs_offset,
>>> +                                   size,
>>> +                                   min_block_size,
>>> +                                   blocks);
>>> +                if (!err)
>>> +                    return 0;
>>> +                if (err != -ENOSPC) {
>>> +                    gpu_buddy_free_list_internal(mm, blocks);
>>> +                    return err;
>>> +                }
>>> +                goto next;
>>> +            }
>>>    -            lhs_size = max((size - filled), min_block_size);
>>> -            if (!IS_ALIGNED(lhs_size, min_block_size))
>>> -                lhs_size = round_up(lhs_size, min_block_size);
>>> +            if (size - filled > rhs_offset)
>>> +                goto next;
>>>    -            /* Allocate blocks traversing LHS */
>>> -            lhs_offset = gpu_buddy_block_offset(block) - lhs_size;
>>> -            err =  __gpu_buddy_alloc_range(mm, lhs_offset, lhs_size,
>>> -                               NULL, &blocks_lhs);
>>> -            if (!err) {
>>> -                list_splice(&blocks_lhs, blocks);
>>> +            lhs_offset = rhs_offset - (size - filled);
>>> +
>>> +            /* Allocate the unaligned LHS offset using round_down */
>>> +            gpu_buddy_free_list_internal(mm, blocks);
>>> +            err = __alloc_contig_aligned_retry(mm, lhs_offset, size,
>>> +                               min_block_size, blocks);
>>> +            if (!err)
>>>                    return 0;
>>> -            } else if (err != -ENOSPC) {
>>> +            if (err != -ENOSPC) {
>>>                    gpu_buddy_free_list_internal(mm, blocks);
>>>                    return err;
>>>                }
>>> -            /* Free blocks for the next iteration */
>>> +next:
>>>                gpu_buddy_free_list_internal(mm, blocks);
>>> -
>>>                iter = rb_prev(iter);
>>>            }
>>>        }
>>>
>>> base-commit: 6648301c5bb2ef23f0fb15bcb01d21ff66f36799