On Fri, 21 Sep 2018, Christoph Hellwig wrote: > On Fri, Sep 21, 2018 at 03:04:18PM +0200, Vitaly Kuznetsov wrote: > > Christoph Hellwig <hch@xxxxxx> writes: > > > > > On Wed, Sep 19, 2018 at 05:15:43PM +0800, Ming Lei wrote: > > >> 1) does kmalloc-N slab guarantee to return N-byte aligned buffer? If > > >> yes, is it a stable rule? > > > > > > This is the assumption in a lot of the kernel, so I think if somethings > > > breaks this we are in a lot of pain. > > > > It seems that SLUB debug breaks this assumption. Kernel built with > > > > CONFIG_SLUB_DEBUG=y > > CONFIG_SLUB=y > > CONFIG_SLUB_DEBUG_ON=y > > Looks like we should fix SLUB debug then.. Nope. We need to not make unwarranted assumptions. Alignment is guaranteed to ARCH_KMALLOC_MINALIGN for kmalloc requests. Fantasizing about alighments and guessing from alignments that result on a particular hardware and slab configuration that these are general does not work.
