linux-kernel - Re: block: DMA alignment of IO buffer allocated from slab

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Message-ID: <20180921130504.GA22551@lst.de>
Date:   Fri, 21 Sep 2018 15:05:04 +0200
From:   Christoph Hellwig <hch@....de>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Christoph Hellwig <hch@....de>, Ming Lei <tom.leiming@...il.com>,
        linux-block <linux-block@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        "open list:XFS FILESYSTEM" <linux-xfs@...r.kernel.org>,
        Dave Chinner <dchinner@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>, Ming Lei <ming.lei@...hat.com>,
        Christoph Lameter <cl@...ux.com>
Subject: Re: block: DMA alignment of IO buffer allocated from slab

On Fri, Sep 21, 2018 at 03:04:18PM +0200, Vitaly Kuznetsov wrote:
> Christoph Hellwig <hch@....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..