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Date: Wed, 6 Jun 2018 23:48:14 +0000
From: Christopher Lameter <cl@linux.com>
Subject: Re: [PATCH] slab: Clean up the code comment in slab kmem_cache
 struct
In-Reply-To: <20180606012624.GA19425@MiWiFi-R3L-srv>
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References: <20180603032402.27526-1-bhe@redhat.com> <01000163d0e8083c-096b06d6-7202-4ce2-b41c-0f33784afcda-000000@email.amazonses.com> <20180606012624.GA19425@MiWiFi-R3L-srv>
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To: Baoquan He <bhe@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org

On Wed, 6 Jun 2018, Baoquan He wrote:

> I am back porting Thomas's sl[a|u]b freelist randomization feature to
> our distros, need go through slab code for better understanding. From
> git log history, they were 'obj_offset' and 'obj_size'. Later on
> 'obj_size' was renamed to 'object_size' in commit 3b0efdfa1e("mm, sl[aou]b:
> Extract common fields from struct kmem_cache") which is from your patch.
> With my understanding, I guess you changed that on purpose because
> object_size is size of each object, obj_offset is for the whole cache,
> representing the offset the real object starts to be stored. And putting
> them separately is for better desribing them in code comment and
> distinction, e.g 'object_size' is in "4) cache creation/removal",
> while 'obj_offset' is put alone to indicate it's for the whole.

obj_offset only applies when CONFIG_SLAB_DEBUG is set. Ok so that screwy
name also indicates that something special goes on.