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Date: Fri, 21 Sep 2018 15:05:04 +0200
From: Christoph Hellwig <hch@lst.de>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>, 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>,
	Christoph Lameter <cl@linux.com>
Subject: Re: block: DMA alignment of IO buffer allocated from slab
Message-ID: <20180921130504.GA22551@lst.de>
References: <CACVXFVOBq3L_EjSTCoiqUL1PH=HMR5EuNNQV0hNndFpGxmUK6g@mail.gmail.com> <20180920063129.GB12913@lst.de> <87h8ij0zot.fsf@vitty.brq.redhat.com>
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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..