From mboxrd@z Thu Jan  1 00:00:00 1970
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Subject: Re: block: DMA alignment of IO buffer allocated from slab
To: Bart Van Assche <bvanassche@acm.org>, Ming Lei <ming.lei@redhat.com>,
 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>, Christoph Lameter <cl@linux.com>,
 Linus Torvalds <torvalds@linux-foundation.org>,
 Greg Kroah-Hartman <gregkh@linuxfoundation.org>
References: <CACVXFVOBq3L_EjSTCoiqUL1PH=HMR5EuNNQV0hNndFpGxmUK6g@mail.gmail.com>
 <20180920063129.GB12913@lst.de> <87h8ij0zot.fsf@vitty.brq.redhat.com>
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 <1537801706.195115.7.camel@acm.org>
 <c844c598-be1d-bef4-fb99-09cf99571fd7@virtuozzo.com>
 <1537804720.195115.9.camel@acm.org>
From: Andrey Ryabinin <aryabinin@virtuozzo.com>
Message-ID: <10c706fd-2252-f11b-312e-ae0d97d9a538@virtuozzo.com>
Date: Mon, 24 Sep 2018 19:07:18 +0300
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On 09/24/2018 06:58 PM, Bart Van Assche wrote:
> On Mon, 2018-09-24 at 18:52 +0300, Andrey Ryabinin wrote:
>> Yes, with CONFIG_DEBUG_SLAB=y, CONFIG_SLUB_DEBUG_ON=y kmalloc() guarantees
>> that result is aligned on ARCH_KMALLOC_MINALIGN boundary.
> 
> Had you noticed that Vitaly Kuznetsov showed that this is not the case? See
> also https://lore.kernel.org/lkml/87h8ij0zot.fsf@vitty.brq.redhat.com/.
> 

I'm not following. On x86-64 ARCH_KMALLOC_MINALIGN is 8, all pointers that Vitaly Kuznetsov showed are 8-byte aligned.

> Thanks,
> 
> Bart.
>