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Message-ID: <20150929091219.40d1e217@redhat.com>
Date: Tue, 29 Sep 2015 09:12:19 +0200
From: Jesper Dangaard Brouer <brouer@...hat.com>
To: Christoph Lameter <cl@...ux.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
netdev@...r.kernel.org,
Alexander Duyck <alexander.duyck@...il.com>,
Pekka Enberg <penberg@...nel.org>,
David Rientjes <rientjes@...gle.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>, brouer@...hat.com
Subject: Re: [PATCH 5/7] slub: support for bulk free with SLUB freelists
On Mon, 28 Sep 2015 11:30:00 -0500 (CDT) Christoph Lameter <cl@...ux.com> wrote:
> On Mon, 28 Sep 2015, Jesper Dangaard Brouer wrote:
>
> > Not knowing SLUB as well as you, it took me several hours to realize
> > init_object() didn't overwrite the freepointer in the object. Thus, I
> > think these comments make the reader aware of not-so-obvious
> > side-effects of SLAB_POISON and SLAB_RED_ZONE.
>
> From the source:
>
> /*
> * Object layout:
> *
> * object address
> * Bytes of the object to be managed.
> * If the freepointer may overlay the object then the free
> * pointer is the first word of the object.
> *
> * Poisoning uses 0x6b (POISON_FREE) and the last byte is
> * 0xa5 (POISON_END)
> *
> * object + s->object_size
> * Padding to reach word boundary. This is also used for Redzoning.
> * Padding is extended by another word if Redzoning is enabled and
> * object_size == inuse.
> *
> * We fill with 0xbb (RED_INACTIVE) for inactive objects and with
> * 0xcc (RED_ACTIVE) for objects in use.
> *
> * object + s->inuse
> * Meta data starts here.
> *
> * A. Free pointer (if we cannot overwrite object on free)
> * B. Tracking data for SLAB_STORE_USER
> * C. Padding to reach required alignment boundary or at mininum
> * one word if debugging is on to be able to detect writes
> * before the word boundary.
Okay, I will remove the comment.
The best doc on SLUB and SLAB layout comes from your slides titled:
"Slab allocators in the Linux Kernel: SLAB, SLOB, SLUB"
Lets gracefully add a link to the slides here:
http://events.linuxfoundation.org/sites/events/files/slides/slaballocators.pdf
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
Author of http://www.iptv-analyzer.org
LinkedIn: http://www.linkedin.com/in/brouer
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