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

On Mon, Aug 31, 2026 at 12:13:08PM +0200, Eli Billauer wrote:

On 30/08/2026 9:47, Mike Rapoport (Microsoft) wrote:

quoted

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And the doc is out of date unfortunately.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.