On Tue, Mar 13, 2018 at 10:19 AM, Christopher Lameter <cl@xxxxxxxxx> wrote: > On Tue, 13 Mar 2018, Shakeel Butt wrote: > >> However for SLUB in debug kernel, the sizes were same. On further >> inspection it is found that SLUB always use kmem_cache.object_size to >> measure the kmem_cache.size while SLAB use the given kmem_cache.size. In >> the debug kernel the slab's size can be larger than its object_size. >> Thus in the creation of non-root slab, the SLAB uses the root's size as >> base to calculate the non-root slab's size and thus non-root slab's size >> can be larger than the root slab's size. For SLUB, the non-root slab's >> size is measured based on the root's object_size and thus the size will >> remain same for root and non-root slab. > > Note that the object_size and size may differ for SLUB based on kernel > parameters and slab configuration. For SLAB these are compilation options. > Thanks for the explanation. >> @@ -379,7 +379,7 @@ struct kmem_cache *find_mergeable(unsigned int size, unsigned int align, >> } >> >> static struct kmem_cache *create_cache(const char *name, >> - unsigned int object_size, unsigned int size, unsigned int align, >> + unsigned int object_size, unsigned int align, >> slab_flags_t flags, unsigned int useroffset, > > Why was both the size and object_size passed during cache creation in the > first place? From the flags etc the slab logic should be able to compute > the actual bytes required for each object and its metadata. > +Vladimir I think it was introduced by 794b1248be4e7 ("memcg, slab: separate memcg vs root cache creation paths") but I could not find out the reason.