On Mon, Nov 26, 2018 at 4:02 PM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > On Fri, Nov 23, 2018 at 01:23:41PM +0100, Vlastimil Babka wrote: > > Is this also true for caches created by kmem_cache_create(), that > > debugging options can result in not respecting the alignment passed to > > kmem_cache_create()? That would be rather bad, IMHO. > > That's what I understood in the discussion. If not it would make > our live simpler, but would need to be well document. >From my experiment, adding `slub_debug` to command line does _not_ break the alignment of kmem_cache_alloc'ed objects. We do see an increase in slab_size (/sys/kernel/slab/io-pgtable_armv7s_l2/slab_size), from 1024 to 3072 (probably because slub needs to allocate space on each side for the red zone/padding, while keeping the alignment?) > Christoph can probably explain the alignment choices in slub. > > > > > > But I do agree with the sentiment of not wanting to spread GFP_DMA32 > > > futher into the slab allocator. > > > > I don't see a problem with GFP_DMA32 for custom caches. Generic > > kmalloc() would be worse, since it would have to create a new array of > > kmalloc caches. But that's already ruled out due to the alignment. > > True, purely slab probably isn't too bad.
