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

[John Olender <john.olender@gmail.com>]

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,
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
>