On Tue, Oct 25, 2022 at 09:52:46PM +0100, Catalin Marinas wrote: > By default kmalloc() returns objects aligned to ARCH_KMALLOC_MINALIGN. > This can be somewhat large on architectures defining ARCH_DMA_MINALIGN > (e.g. 128 on arm64) and significant memory is wasted through small > kmalloc() allocations. > > Reduce the minimum alignment for kmalloc() to the default > KMALLOC_MIN_SIZE (8 for slub, 32 for slab) but align the > requested size to the bigger ARCH_KMALLOC_MINALIGN unless a newly added > __GFP_PACKED flag is passed. With this gfp flag, the alignment is > reduced to KMALLOC_PACKED_ALIGN, at least sizeof(unsigned long long). Can memory allocated with __GFP_PACKED be sent to DMA controllers? If not, you should say that somewhere here or I'm going to get a bunch of patches trying to add this flag to tiny USB urb allocations (where we allocate 8 or 16 bytes) that is then going to fail on some hardware. thanks, greg k-h
