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

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Message-ID: <alpine.DEB.2.11.1507171008080.17929@east.gentwo.org>
Date:	Fri, 17 Jul 2015 10:09:49 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Konstantin Khlebnikov <koct9i@...il.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 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.

> 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.

> 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?


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