Re: [RFC PATCH] mm/sparse: remove sparse_buffer

[David Hildenbrand (Arm)]

On 4/10/26 08:05, Muchun Song wrote:
> 
> 
>> On Apr 10, 2026, at 11:07, Muchun Song <muchun.song@xxxxxxxxx> wrote:
>>
>>
>>
>>>
>>> Hi,
>>>
>>>
>>> memblock always allocates in order, so if there are no other memblock
>>> allocations between the calls to memmap_alloc(), all these allocations will
>>> be together and they all will be coalesced to a single region in
>>> memblock.reserved.
>>>
>>>
>>> ...
>>>
>>>
>>> memmap_alloc() will be slower than sparse_buffer_alloc(), allocating from
>>> memblock is more involved that sparse_buffer_alloc(), but without
>>> measurements it's hard to tell how much it'll affect overall sparse_init().
>>
>> I ran a test on a 256GB VM, and the results are as follows:
>>
>> With patch:    741,292 ns
>> Without patch: 199,555 ns
>>
>> The performance is approximately 3.7x slower with the patch applied.
> 
> I also tested 512GB of data, and the results were roughly twice that
> of 256GB, so for a 1TB machine, the memory allocation time is only a
> few milliseconds. It seems we don’t need to worry about the 3.7x
> performance drop.

Good. Can you incorporate all that into the patch description?

-- 
Cheers,

David