On Thu, Mar 29, 2018 at 03:42:59PM +0200, Hans de Goede wrote:
Hi,
On 29-03-18 13:58, Greg Kroah-Hartman wrote:
On Thu, Mar 29, 2018 at 01:21:15PM +0200, Hans de Goede wrote:
It is not possible to get DMA32 zone memory through kmalloc,
Why can't we just fix that issue here instead?
AFAIK that would go against the design of the whole slab allocator, it creates buckets (kmem_cache objects) for differently sized allocs out of the normal memzone, you cannot select what memzone you want with kmalloc, if you need to specify a memzone you need to use either dma specific malloc functions such as the dmapool.h functions, or directly call alloc_pages / get_free_pages.
A quick grep on the drivers dir shows 50 files using GFP_DMA32 and almost all are passing it to alloc_page or __get_page.
If there are 50 users of such an api, why is the mm core not handling this for drivers automatically? It seems harsh that they all have to do this type of allocation on their own.
I do actually see 2 drivers which are passing it to kmalloc, which as said will not work I will mail the maintainers of those about this.
If they haven't noticed that their hardware isn't working, perhaps they don't need to set that flag? :)
thanks,
greg k-h