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

On Tue, 1 Sep 2026 10:59:16 +0300
Mike Rapoport [off-list ref] wrote:

On Mon, Aug 31, 2026 at 12:39:37PM +0100, David Laight wrote:

quoted

On Mon, 31 Aug 2026 12:13:08 +0200
Eli Billauer [off-list ref] wrote:
  

quoted

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).  

Would it really make sense to allocate the four buffers separately?
And/or use vmalloc().  

My understanding is that the buffers don't need to be physically
contiguous and vmalloc()ing the entire fifo->mem in one go should work.

What is the minimum size?
Remember PAGE_SIZE can be 64k.

David

Eli, what do you think?
 

quoted

David