Re: [PATCH] cnic: change __GFP_COMP allocation method

Christoph Hellwig
2023-12-19T05:58:34Z

On Tue, Dec 19, 2023 at 11:25:14AM +0530, Nilesh Javali wrote:
> The dma_alloc_coherent no more provide __GFP_COMP allocation as per commit,
> dma-mapping: reject __GFP_COMP in dma_alloc_attrs, and hence
> instead use __get_free_pages for __GFP_COMP allocation along with
> dma_map_single to get dma address in order to fix page reference counting
> issue caused in iscsiuio mmap.

You can't just do a single map for things mapped to userspace, as that
breaks setups that are not DMA coherent. There was a patch floating
around to explicitly support dma coherent allocations in uio, which is
the right thing to do.