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Date: Tue, 26 Jan 2016 16:03:20 +0900
From: Joonsoo Kim <>
To: Laura Abbott <>
Cc: Christoph Lameter <>, Pekka Enberg <>,
	David Rientjes <>,
	Andrew Morton <>,,,,
	Kees Cook <>
Subject: Re: [RFC][PATCH 0/3] Speed up SLUB poisoning + disable checks

On Mon, Jan 25, 2016 at 05:15:10PM -0800, Laura Abbott wrote:
> Hi,
> Based on the discussion from the series to add slab sanitization
> (<>)
> the existing SLAB_POISON mechanism already covers similar behavior.
> The performance of SLAB_POISON isn't very good. With hackbench -g 20 -l 1000
> on QEMU with one cpu:

I doesn't follow up that discussion, but, I think that reusing
SLAB_POISON for slab sanitization needs more changes. I assume that
completeness and performance is matter for slab sanitization.

1) SLAB_POISON isn't applied to specific kmem_cache which has
constructor or SLAB_DESTROY_BY_RCU flag. For debug, it's not necessary
to be applied, but, for slab sanitization, it is better to apply it to
all caches.

2) SLAB_POISON makes object size bigger so natural alignment will be
broken. For example, kmalloc(256) cache's size is 256 in normal
case but it would be 264 when SLAB_POISON is enabled. This causes
memory waste.

In fact, I'd prefer not reusing SLAB_POISON. It would make thing
simpler. But, it's up to Christoph.


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