On Fri, Oct 09, 2026 at 04:22:03PM +0200, Harry Yoo wrote: > And now I see the initial kmem_buckets design did not sufficiently > tackle the question "How this should work when kmem_buckets falls back > to kmalloc?" > > I suppose the kmem_buckets' abstraction should not be too tightly > coupled with kmalloc caches. Creating a kmem_buckets should be > conceptually equivalent to creating a set of caches with speicifc > slab flags, size, align, useroffset/size. (for variable size allocation).
Just to clarify... I have a few concerns on this area. 1. Complexity. It's very counter-intuitive to understand how it works when SLAB_BUCKETS is not compiled. My brain cannot easily process two different implementations w/ and w/o SLAB_BUCKETS. A "compatibility layer" allows us to assume certain expectations and ignore all implementation details when SLAB_BUCKETS is not compiled. 2. Making kmem_buckets tightly coupled with kmalloc's implementation details is not reasonable. Let's say, at some point we make SLAB_BUCKETS always enabled and drop the config option. Then all kmem_buckets users will now have certain assumptions inherted from kmalloc (e.g. alignment), which is not reasonable. 3. __GFP_ACCOUNT and __GFP_DMA should be applied to all allocations in the slab cache. For kmalloc, these flags are only used to select the kmalloc cache (which has equivalent SLAB_* flags for __GFP_ACCOUNT or __GFP_DMA) to serve the allocation. Specifying it on individual allocations (rather than as SLAB_ flags) makes it easy to break the assumption. > When it falls back to kmalloc, kmem_buckets itself should provide a > compatibility layer when falling back to kmalloc. For example, calculate_sizes() converts certain SLAB_* flags into GFP flags (s->allocflags) for allocation. We can have a similar logic when falling back to kmalloc. Though current implementation does not allow this and requires some rework. -- Cheers, Harry / Hyeonggon
