Re: [PATCH net-next v6 0/8] net: skb: isolate skb data area allocations into a separate bucket

On Tue, Oct 06, 2026 at 02:20:26AM -0700, Kees Cook wrote:

Hi!

Hi Kees!

Was hoping to say hi to you at LPC but I missed the chance ;)
Maybe next time. Safe travels!

Uh, my mailbox stopped working for a few days as I forgot to renew
subscription. (Kiryl told me it's bouncing, thanks!) Hopefully I didn't
miss too much...

This gets the buckets able to handle memcg (GFP_KERNEL_ACCOUNT) with
isolation (since it's common due to AF_UNIX),

Cool!

and GFP_DMA with fall back
(since it's rare).

It gave me an excuse to build out bucket kunit tests
too, and that (and LLM review) found a couple other issues that needed
fixing too, including msg_msg allocations going uncharged to their memcg
when CONFIG_SLAB_BUCKETS=n (fixed in 2/8).

Oh.

Harry, on your v4 question[1] about bucket users giving their own
alignment: I tried that in v5, but a set's allocations don't always
come from its own caches. With CONFIG_SLAB_BUCKETS=n, after a failed
kmem_buckets_create(), and for the DMA and reclaimable fallbacks, they
come from the general kmalloc caches, which can only give kmalloc()'s
alignment.

So v6 goes back to mirroring the kmalloc cache's alignment,

I might be missing something, but why is that a problem?

For kmem_buckets users, the reason* to specify alignment is because
they might need less strict alignment than kmalloc.

(*Perhaps it's nice to document that in the comment)

However, because kmem_buckets can fall back to kmalloc on e.g. kernels
w/o CONFIG_SLAB_BUCKETS, it should be fine to fall back. No?

Creating kmem_buckets with more strict alignment than
kmalloc doesn't make sense. 

and drops the ctor and flags arguments for the same reason.

Uh, for ctor and flags, yes. We can't have them in kmem_buckets.

And the whole
exploration made me realize I had a completely wrong understanding of
how memcg worked. :P

The bulk of this is mm/slab, but the final patch is netdev, which Paolo
acked in v4, so I'm hoping this whole series can go via slab?

Going thorough slab/for-next sounds reasonable to me once it gets
some reviews.

Vlastimil?

-- 
Cheers,
Harry / Hyeonggon