Re: [Chapter One] THP zones: the use cases of policy zones

[Vlastimil Babka <vbabka@suse.cz>]

On 3/5/24 09:41, Barry Song wrote:
> We did implement similar idea in the pageblock granularity on OPPO's
> phones by extending two special migratetypes[1]:
> 
> * QUAD_TO_TRIP - this is mainly for 4-order mTHP allocation which can use
> ARM64's CONT-PTE; but can rarely be splitted into 3 order to dull the pain
> of 3-order allocation if and only if 3-order allocation has failed in both
> normal buddy and the below TRIP_TO_QUAD.
>   
> * TRIP_TO_QUAD - this is mainly for 4-order mTHP allocation which can use
> ARM64's CONT-PTE; but can sometimes be splitted into 3 order to dull the
> pain of 3-order allocation if and only if 3-order allocation has failed in
> normal buddy.
> 
> neither of above will be merged into 5 order or above; neither of above
> will be splitted into 2 order or lower.
> 
> in compaction, we will skip both of above. I am seeing one disadvantage
> of this approach is that I have to add a separate LRU list in each
> zone to place those mTHP folios. if mTHP and small folios are put
> in the same LRU list, the reclamation efficiency is extremely bad.
> 
> A separate zone, on the other hand, can avoid a separate LRU list
> for mTHP as the new zone has its own LRU list.

But we switched from per-zone to per-node LRU lists years ago?
Is that actually a complication for the policy zones? Or does this work
silently assume multigen lru which (IIRC) works differently?


> [1] https://github.com/OnePlusOSS/android_kernel_oneplus_sm8650/blob/oneplus/sm8650_u_14.0.0_oneplus12/mm/page_alloc.c
> 
>>
>> [1] https://lore.kernel.org/20240215103205.2607016-1-ryan.roberts@arm.com/
>> [2] https://lore.kernel.org/20200928175428.4110504-1-zi.yan@sent.com/
>>
>> Signed-off-by: Yu Zhao <yuzhao@google.com>
> 
> Thanks
> Barry
> 
>