From: Alan Stern > Sent: 22 June 2021 14:29 ... > > Thought... > > > > Is kmalloc(1, GFP_KERNEL) guaranteed to return a pointer into > > a cache line that will not be accessed by any other code? > > (This is slightly weaker than requiring a cache-line aligned > > pointer - but very similar.) > > As I understand it, on architectures that do not have cache-coherent > I/O, kmalloc is guaranteed to return a buffer that is > cacheline-aligned and whose length is a multiple of the cacheline > size. > > Now, whether that buffer ends up being accessed by any other code > depends on what your driver does with the pointer it gets from > kmalloc. :-) Thanks for the clarification. Most of the small allocates in the usb stack are for transmits where it is only necessary to ensure a cache write-back. I know there has been some confusion because one of the allocators can add a small header to every allocation. This can lead to unexpectedly inadequately aligned pointers. If it is updated when the preceding block is freed (as some user-space mallocs do) then it would need to be in a completely separate cache line. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
