Re: [PATCH v6 1/2] gpu/buddy: restore two-pass clear/dirty guard for range-biased allocation

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

On 10/21/2026 6:19 PM, Matthew Auld wrote:
> On 21/10/2026 13:18, Arunpravin Paneer Selvam wrote:
>> From: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
>>
>> Range-restricted allocations (the visible-VRAM aperture) skip
>> dirty_steer_window() and reach __alloc_range_bias() with no clear/dirty
>> eligibility guard, so a dirty allocation freely splits clear extents 
>> (and
>> vice versa), interleaving the two classes until no large same-class run
>> survives and a 4K scanout pin fails with -ENOSPC. Use a two-pass range
>> search instead: block_incompatible() rejects opposite-class blocks in 
>> the
>> strict pass and relaxes only when the strict pass returns -ENOSPC, so a
>> request still succeeds when only opposite-class space remains. A KUnit
>> regression test covers the interleaving pattern and fails without the
>> guard.
>>
>> v2: the strict pass can split a block and then reject both children, so
>>      a split no longer implies a compatible block exists. Sashiko 
>> reported
>>      the resulting leaked splits; fix as suggested by Matthew:
>>   - Push the parent back on the DFS stack after each split and merge it
>>     back with unsplit_block() if both children are still free.
>>   - Make block_incompatible() judge free blocks only (split nodes keep a
>>     stale clear bit) and take the requested order, so mixed blocks that
>>     can hold a compatible block are descended instead of skipped.
>>   - Extend the KUnit test with a coalesced mixed block and a check that
>>     a rejected split is merged back.
>>
>> Fixes: 1ad5e807f716 ("gpu/buddy: replace dual-tree/force_merge with 
>> decoupled dirty tracker")
>> Assisted-by: LLM
>> Cc: Matthew Auld <matthew.auld@intel.com>
>> Cc: Christian König <christian.koenig@amd.com>
>> Signed-off-by: Arunpravin Paneer Selvam 
>> <Arunpravin.PaneerSelvam@amd.com>
>
> Reviewed-by: Matthew Auld <matthew.auld@intel.com>
>
> Are you just going to push this one by itself?
Yes, I am planning to push this one separately. Patch 2 can follow later 
after review.

Thanks,
Arun.