linux-kernel - Re: [PATCH 2/2] mm/slub: disable merging after enabling debug in runtime

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Message-ID: <CALYGNiM6iKzwSiKRu79N-pjnSQZR_P3t9q50vV3cHtvLQz=dCA@mail.gmail.com>
Date:	Fri, 17 Jul 2015 12:37:40 +0300
From:	Konstantin Khlebnikov <koct9i@...il.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] mm/slub: disable merging after enabling debug in runtime

On Wed, Jul 15, 2015 at 12:18 AM, Christoph Lameter <cl@...ux.com> wrote:
>
> On Tue, 14 Jul 2015, Konstantin Khlebnikov wrote:
>> > What breaks?
>>
>> The same commands from first patch:
>>
>> # echo 1 | tee /sys/kernel/slab/*/sanity_checks
>> # modprobe configfs
>>
>> loading configfs now fails (without crashing kernel though) because of
>> "sysfs: cannot create duplicate filename '/kernel/slab/:t-0000096'"
>
> Hrm.... Bad. Maybe drop the checks for the debug options that can be
> configured when merging slabs? They do not influence the object layout
> per definition.

I don't understand that. Debug options do changes in object layout.

Since they add significant performance overhead and cannot be undone in runtime
it's unlikely that anyone who uses them don't care about merging after that.
Also I don't see how merging could affect debugging in positive way
(except debugging bugs in merging logic itself).
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