Date: Tue, 14 Jul 2015 13:11:42 -0500 (CDT)
From: Christoph Lameter <cl@linux.com>
To: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] mm/slub: disable merging after enabling debug in
 runtime
In-Reply-To: <20150714131705.21442.99279.stgit@buzz>
Message-ID: <alpine.DEB.2.11.1507141304430.28065@east.gentwo.org>
References: <20150714131704.21442.17939.stgit@buzz> <20150714131705.21442.99279.stgit@buzz>
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On Tue, 14 Jul 2015, Konstantin Khlebnikov wrote:

> Enabling debug in runtime breaks creation of new kmem caches:
> they have incompatible flags thus cannot be merged but unique
> names are taken by existing caches.

What breaks?

Caches may already have been merged and thus the question is what to do
about a cache that has multiple aliases if a runtime option is requested.
The solution that slub implements is to only allow a limited number of
debug operations to be enabled. Those then will appear to affect all
aliases of course.

Creating additional caches later may create additional
aliasing which will then restrict what options can be changed.

Other operations are also restricted depending on the number of objects
stored in a cache. A cache with zero objects can be easily reconfigured.
If there are objects then modifications that impact object size are not
allowed anymore.
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