netdev - Re: [PATCH bpf-next 03/29] bpf: introduce BPF token object

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Date: Fri, 5 Jan 2024 20:32:49 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Linus Torvalds <torvalds@...uxfoundation.org>
Cc: Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
	netdev@...r.kernel.org, paul@...l-moore.com, brauner@...nel.org,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH bpf-next 03/29] bpf: introduce BPF token object

On Fri, Jan 05, 2024 at 12:25:42PM -0800, Linus Torvalds wrote:
> > diff --git a/kernel/bpf/token.c b/kernel/bpf/token.c
> > +
> > +static void bpf_token_free(struct bpf_token *token)
> > +{
> > +       put_user_ns(token->userns);
> > +       kvfree(token);
> > +}
> 
> > +int bpf_token_create(union bpf_attr *attr)
> > +{
> > ....
> > +       token = kvzalloc(sizeof(*token), GFP_USER);
> 
> Ok, so the kvzalloc() and kvfree() certainly line up, but why use them at all?
> 
> kvmalloc() and friends are for "use kmalloc, and fall back on vmalloc
> for big allocations when that fails".
> 
> For just a structure, a plain 'kzalloc()/kfree()' pair would seem to
> make much more sense.

I can't tell from the description whether there are going to be a lot of
these.  If there are, it might make sense to create a slab cache for
them rather than get them from the general-purpose kmalloc caches.