Re: [PATCH] audit: remove the audit freelist

[Florian Westphal <fw@strlen.de>]

Paul Moore <paul@paul-moore.com> wrote:
> On Wed, Nov 30, 2016 at 8:44 PM, Florian Westphal <fw@strlen.de> wrote:
> > Paul Moore <paul@paul-moore.com> wrote:
> >> On Tue, Nov 15, 2016 at 8:16 AM, Florian Westphal <fw@strlen.de> wrote:
> >> > allows better debugging as freeing audit buffers now always honors slub
> >> > debug hooks (e.g. object poisoning) and leak checker can detect the
> >> > free operation.
> >> >
> >> > Removal also results in a small speedup (using
> >> > single rule 'iptables -A INPUT -i lo -j AUDIT --type drop'):
> >> >
> >> > super_netperf 4 -H 127.0.0.1 -l 360 -t UDP_RR -- -R 1 -m 64
> >> > Before:
> >> > 294953
> >> > After:
> >> > 298013
> >> >
> >> > (alloc/free no longer serializes on spinlock, allocator can use percpu
> >> >  pool).
> >> >
> >> > Signed-off-by: Florian Westphal <fw@strlen.de>
> >> > ---
> >> >  kernel/audit.c | 53 ++++++++---------------------------------------------
> >> >  1 file changed, 8 insertions(+), 45 deletions(-)
> >>
> >> Sorry for the delay, I was hoping to have some time to play around
> >> with this and offer a more meaningful comment ... I've often wondered
> >> about converting audit_buffer, and audit_context for that matter, over
> >> to their own kmem_cache; have you considered that?  Or was this
> >> proposed due to simplicity?
> >
> > Not sure I understand, you could still convert it on top of this.
> > (Although audit_buffer is just 24 bytes after this patch so it will
> >  come from 32byte kmalloc slab).
> 
> I'm not arguing against this patch, partly just musing out loud,
> partly just seeing if you had experimented with creating a
> audit_buffer specific kmem_cache (I'm guessing the answer here is
> "no").  If we do convert to a kmem_cache this patch would be the
> obvious first step.

It does convert to a kmem_cache, indirectly.

kmalloc() uses builtin_constant_size() magic to resolve the kmalloc to
kmem_cache_alloc, using the precreated kmalloc_caches[] in slab_common.c .