From: Christopher Lameter <cl@linux.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>,
Ming Lei <tom.leiming@gmail.com>,
linux-block <linux-block@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
Linux FS Devel <linux-fsdevel@vger.kernel.org>,
"open list:XFS FILESYSTEM" <linux-xfs@vger.kernel.org>,
Dave Chinner <dchinner@redhat.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Jens Axboe <axboe@kernel.dk>, Ming Lei <ming.lei@redhat.com>
Subject: Re: block: DMA alignment of IO buffer allocated from slab
Date: Mon, 24 Sep 2018 16:06:28 +0000 [thread overview]
Message-ID: <010001660c54fb65-b9d3a770-6678-40d0-8088-4db20af32280-000000@email.amazonses.com> (raw)
In-Reply-To: <20180921130504.GA22551@lst.de>
On Fri, 21 Sep 2018, Christoph Hellwig wrote:
> On Fri, Sep 21, 2018 at 03:04:18PM +0200, Vitaly Kuznetsov wrote:
> > Christoph Hellwig <hch@lst.de> writes:
> >
> > > On Wed, Sep 19, 2018 at 05:15:43PM +0800, Ming Lei wrote:
> > >> 1) does kmalloc-N slab guarantee to return N-byte aligned buffer? If
> > >> yes, is it a stable rule?
> > >
> > > This is the assumption in a lot of the kernel, so I think if somethings
> > > breaks this we are in a lot of pain.
> >
> > It seems that SLUB debug breaks this assumption. Kernel built with
> >
> > CONFIG_SLUB_DEBUG=y
> > CONFIG_SLUB=y
> > CONFIG_SLUB_DEBUG_ON=y
>
> Looks like we should fix SLUB debug then..
Nope. We need to not make unwarranted assumptions. Alignment is guaranteed
to ARCH_KMALLOC_MINALIGN for kmalloc requests. Fantasizing about
alighments and guessing from alignments that result on a particular
hardware and slab configuration that these are general does not work.
next prev parent reply other threads:[~2018-09-24 16:06 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-19 9:15 block: DMA alignment of IO buffer allocated from slab Ming Lei
2018-09-19 9:41 ` Vitaly Kuznetsov
2018-09-19 10:02 ` Ming Lei
2018-09-19 11:15 ` Vitaly Kuznetsov
2018-09-20 1:28 ` Ming Lei
2018-09-20 3:59 ` Yang Shi
2018-09-20 6:32 ` Christoph Hellwig
2018-09-20 6:31 ` Christoph Hellwig
2018-09-21 13:04 ` Vitaly Kuznetsov
2018-09-21 13:05 ` Christoph Hellwig
2018-09-21 15:00 ` Jens Axboe
2018-09-24 16:06 ` Christopher Lameter [this message]
2018-09-24 17:49 ` Jens Axboe
2018-09-24 18:00 ` Christopher Lameter
2018-09-24 18:09 ` Jens Axboe
2018-09-25 7:49 ` Dave Chinner
2018-09-25 15:44 ` Jens Axboe
2018-09-25 21:04 ` Matthew Wilcox
2018-09-23 22:42 ` Ming Lei
2018-09-24 9:46 ` Andrey Ryabinin
2018-09-24 14:19 ` Bart Van Assche
2018-09-24 14:43 ` Andrey Ryabinin
2018-09-24 15:08 ` Bart Van Assche
2018-09-24 15:52 ` Andrey Ryabinin
2018-09-24 15:58 ` Bart Van Assche
2018-09-24 16:07 ` Andrey Ryabinin
2018-09-24 16:19 ` Bart Van Assche
2018-09-24 16:47 ` Christopher Lameter
2018-09-24 18:57 ` Matthew Wilcox
2018-09-24 19:56 ` Bart Van Assche
2018-09-24 20:41 ` Matthew Wilcox
2018-09-24 20:54 ` Bart Van Assche
2018-09-24 21:09 ` Matthew Wilcox
2018-09-25 0:16 ` Ming Lei
2018-09-25 3:28 ` Matthew Wilcox
2018-09-25 4:10 ` Bart Van Assche
2018-09-25 4:44 ` Matthew Wilcox
2018-09-25 6:55 ` Ming Lei
2018-09-24 15:17 ` Christopher Lameter
2018-09-25 0:20 ` Ming Lei
2018-09-20 14:07 ` Bart Van Assche
2018-09-21 1:56 ` Dave Chinner
2018-09-21 7:08 ` Christoph Hellwig
2018-09-21 7:25 ` Ming Lei
2018-09-21 14:59 ` Jens Axboe
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