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

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Message-ID: <55A91E4D.2080203@yandex-team.ru>
Date:	Fri, 17 Jul 2015 18:25:01 +0300
From:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:	Christoph Lameter <cl@...ux.com>,
	Konstantin Khlebnikov <koct9i@...il.com>
CC:	"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 17.07.2015 18:09, Christoph Lameter wrote:
> On Fri, 17 Jul 2015, Konstantin Khlebnikov wrote:
>
>>> 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.
>
> Only some debug options change the object layout and those are alrady
> forbidden for caches with objects.

Ah, ok. I've missed that any_slab_objects(). Never used enabling these 
features in runtime.

>
>> 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.
>
> Those that do not affect the object layout can be undone.

Except __CMPXCHG_DOUBLE. But I guess we can use stop-machine for that.

>
>> Also I don't see how merging could affect debugging in positive way
>> (except debugging bugs in merging logic itself).
>
> The problem here is that debugging is switched on for slabs that are
> already merged right?
>

Right. And looks like problem only in conflicting sysfs names.

-- 
Konstantin
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