On Mon, 11 Jun 2007, Håvard Skinnemoen wrote: > > Note that I do not get why you would be aligning the objects to 32 bytes. > > Increasing the smallest cache size wastes a lot of memory. And it is > > usually advantageous if multiple related objects are in the same cacheline > > unless you have heavy SMP contention. > > It's not about performance at all, it's about DMA buffers allocated > using kmalloc() getting corrupted. Imagine this:
Uhhh... How about using a separate slab for the DMA buffers? > Maybe there are other solutions to this problem, but the old SLAB > allocator did guarantee 32-byte alignment as long as SLAB debugging > was turned off, so setting ARCH_KMALLOC_MINALIGN seemed like the > easiest way to get back to the old, known-working behaviour. SLABs mininum object size is 32 thus you had no problems. I see. SLAB does not guarantee 32 byte alignment. It just happened to work. If you switch on CONFIG_SLAB_DEBUG you will likely get into trouble. So I'd suggest to set up a special slab for your DMA buffers.