Subject: Re: [RFC][PATCH] mm/slub.c: Allow poisoning to use the fast path
To: Christopher Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Kees Cook <keescook@chromium.org>,
        Rik van Riel <riel@redhat.com>
References: <20170804231002.20362-1-labbott@redhat.com>
 <alpine.DEB.2.20.1708070936400.17268@nuc-kabylake>
From: Laura Abbott <labbott@redhat.com>
Message-ID: <559096f0-bf1b-eff1-f0ce-33f53a4df255@redhat.com>
Date: Mon, 7 Aug 2017 10:48:42 -0700
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On 08/07/2017 07:37 AM, Christopher Lameter wrote:
> On Fri, 4 Aug 2017, Laura Abbott wrote:
> 
>> All slub debug features currently disable the fast path completely.
>> Some features such as consistency checks require this to allow taking of
>> locks. Poisoning and red zoning don't require this and can safely use
>> the per-cpu fast path. Introduce a Kconfig to continue to use the fast
>> path when 'fast' debugging options are enabled. The code will
>> automatically revert to always using the slow path when 'slow' options
>> are enabled.
> 
> Ok I see that the objects are initialized with poisoning and redzoning but
> I do not see that there is fastpath code to actually check the values
> before the object is reinitialized. Is that intentional or am
> I missing something?
> 

Yes, that's intentional here. I see the validation as a separate more
expensive feature. I had a crude patch to do some checks for testing
and I know Daniel Micay had an out of tree patch to do some checks
as well.

Thanks,
Laura