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01:52:09PM +0800, Hao Li wrote: > > > On Mon, Jan 05, 2026 at 05:02:30PM +0900, Harry Yoo wrote: > > > > When a cache has high s->align value and s->object_size is not aligned > > > > to it, each object ends up with some unused space because of alignment. > > > > If this wasted space is big enough, we can use it to store the > > > > slabobj_ext metadata instead of wasting it. > > > > > > Hi, Harry, > > > > Hi Hao, > > > > > When we save obj_ext in s->size space, it seems that slab_ksize() might > > > be missing the corresponding handling. > > > > Oops. > > > > > It still returns s->size, which could cause callers of slab_ksize() > > > to see unexpected data (i.e. obj_ext), or even overwrite the obj_ext data. > > > > Yes indeed. > > Great point, thanks! > > > > I'll fix it by checking if the slab has obj_exts within the object > > layout and returning s->object_size if so. > > Makes sense - I think there's one more nuance worth capturing. > slab_ksize() seems to compute the maximum safe size by applying layout > constraints from most-restrictive to least-restrictive: > redzones/poison/KASAN clamp it to object_size, tail metadata > (SLAB_TYPESAFE_BY_RCU / SLAB_STORE_USER) clamps it to inuse, and only > when nothing metadata lives does it return s->size. Waaaait, SLAB_TYPESAFE_BY_RCU isn't the only case where we put freelist pointer after the object. What about caches with constructor? We do place it after object, but slab_ksize() may return s->size? -- Cheers, Harry / Hyeonggon