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

[Muchun Song <muchun.song@linux.dev>]

> On Apr 10, 2026, at 15:44, David Hildenbrand (Arm) <david@kernel.org> wrote:
> 
> On 4/10/26 08:05, Muchun Song wrote:
>> 
>> 
>>> On Apr 10, 2026, at 11:07, Muchun Song <muchun.song@linux.dev> 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?
> 

Yes. No problem.

> -- 
> Cheers,
> 
> David