Date: Wed, 12 Jul 2017 09:49:11 -0500 (CDT)
From: Christopher Lameter <cl@linux.com>
To: Joonsoo Kim <js1304@gmail.com>
cc: Laura Abbott <labbott@redhat.com>, Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Kees Cook <keescook@chromium.org>
Subject: Re: [RFC][PATCH] slub: Introduce 'alternate' per cpu partial lists
In-Reply-To: <20170614044528.GA5924@js1304-desktop>
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On Wed, 14 Jun 2017, Joonsoo Kim wrote:

> > - Some of this code is redundant and can probably be combined.
> > - The fast path is very sensitive and it was suggested I leave it alone. The
> > approach I took means the fastpath cmpxchg always fails before trying the
> > alternate cmpxchg. From some of my profiling, the cmpxchg seemed to be fairly
> > expensive.
>
> It looks better to modify the fastpath for non-debuging poisoning. If
> we use the jump label, it doesn't cause any overhead to the fastpath
> for the user who doesn't use this feature. It really makes thing
> simpler. Only a few more lines will be needed in the fastpath.
>
> Christoph, any opinion?

Just looked through it. Sorry was on vacation in Europe for awhile.

The duplication in kmem_cache_cpu is not good performance wise. Maybe just
keep the single per cpu partial list and depending on a kmem_cache flag
change the locking semantics in order to allow for faster debugging?