linux-kernel - Re: [RFC][PATCH] slub: Introduce 'alternate' per cpu partial lists

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Date:   Wed, 12 Jul 2017 09:49:11 -0500 (CDT)
From:   Christopher Lameter <cl@...ux.com>
To:     Joonsoo Kim <js1304@...il.com>
cc:     Laura Abbott <labbott@...hat.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>
Subject: Re: [RFC][PATCH] slub: Introduce 'alternate' per cpu partial lists

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?