linux-kernel - Re: [PATCH v3 11/21] slab: remove SLUB_CPU

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <aXAmnbhynV3xUKPW@hyeyoo>
Date: Wed, 21 Jan 2026 10:06:37 +0900
From: Harry Yoo <harry.yoo@...cle.com>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: Vlastimil Babka <vbabka@...e.cz>, Petr Tesarik <ptesarik@...e.com>,
        Christoph Lameter <cl@...two.org>,
        David Rientjes <rientjes@...gle.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>, Hao Li <hao.li@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Uladzislau Rezki <urezki@...il.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Alexei Starovoitov <ast@...nel.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev,
        bpf@...r.kernel.org, kasan-dev@...glegroups.com
Subject: Re: [PATCH v3 11/21] slab: remove SLUB_CPU_PARTIAL

On Wed, Jan 21, 2026 at 09:58:40AM +0900, Harry Yoo wrote:
> On Tue, Jan 20, 2026 at 10:25:27PM +0000, Suren Baghdasaryan wrote:
> > On Fri, Jan 16, 2026 at 2:40 PM Vlastimil Babka <vbabka@...e.cz> wrote:
> > > @@ -5744,10 +5553,9 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab,
> > >
> > >         /*
> > >          * Objects left in the slab. If it was not on the partial list before
> > > -        * then add it. This can only happen when cache has no per cpu partial
> > > -        * list otherwise we would have put it there.
> > > +        * then add it.
> > >          */
> > > -       if (!IS_ENABLED(CONFIG_SLUB_CPU_PARTIAL) && unlikely(was_full)) {
> > > +       if (unlikely(was_full)) {
> > 
> > This is not really related to your change but I wonder why we check
> > for was_full to detect that the slab was not on partial list instead
> > of checking !on_node_partial... They might be equivalent at this point
> > but it's still a bit confusing.
> 
> If we only know that a slab is not on the partial list, we cannot
> manipulate its list because it may be on a linked list that cannot
> handle list manipulation outside function
> (e.g., pc.slabs in __refill_objects()).
> 
> If it's not on the partial list, we can safely manipulate the list
> only when we know it was full. It's safe because full slabs are not
> supposed to be on any list (except for debug caches, where frees are
> done via free_to_partial_list()).

Of course, when a slab was frozen, this doesn't apply and __slab_free()
explicitly handles that case.

-- 
Cheers,
Harry / Hyeonggon