Re: [PATCH 2/4] char: xillybus: replace __get_free_pages() with kmalloc()

[Mike Rapoport <rppt@kernel.org>]

On Mon, Aug 31, 2026 at 12:13:08PM +0200, Eli Billauer wrote:
> On 30/08/2026 9:47, Mike Rapoport (Microsoft) wrote:
> > fifo_init() allocates the buffers backing the software FIFO and
> > endpoint_alloc() allocates the transfer buffers of a USB endpoint.
> > 
> > These buffers can be allocated with kmalloc() as there's nothing special
> > about them to go directly to the page allocator.
> 
> Except that they are a bit large.
> 
> fifo_init() may be requested to allocate up to 256 MB of buffer memory. This
> memory resource is split into an array of buffers (fifo->mem[i]), each 64
> kiB (or less, if there's trouble obtaining segments of this size).
> 
> Citing Documentation/core-api/memory-allocation.rst:
> 
> "The maximal size of a chunk that can be allocated with `kmalloc` is
> limited. The actual limit depends on the hardware and the kernel
> configuration, but it is a good practice to use `kmalloc` for objects
> smaller than page size."

For large sizes kmalloc falls back to page allocator anyway.

And the doc is out of date unfortunately.
 
> Regards,
>    Eli

-- 
Sincerely yours,
Mike.