From: Bart Van Assche <bvanassche@acm.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>,
Ming Lei <ming.lei@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
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>
Subject: Re: block: DMA alignment of IO buffer allocated from slab
Date: Mon, 24 Sep 2018 13:54:01 -0700 [thread overview]
Message-ID: <1537822441.195115.32.camel@acm.org> (raw)
In-Reply-To: <20180924204148.GA2542@bombadil.infradead.org>
On Mon, 2018-09-24 at 13:41 -0700, Matthew Wilcox wrote:
> On Mon, Sep 24, 2018 at 12:56:18PM -0700, Bart Van Assche wrote:
> > On Mon, 2018-09-24 at 11:57 -0700, Matthew Wilcox wrote:
> > > You're not supposed to use kmalloc memory for DMA. This is why we have
> > > dma_alloc_coherent() and friends.
> >
> > Are you claiming that all drivers that use DMA should use coherent DMA only? If
> > coherent DMA is the only DMA style that should be used, why do the following
> > function pointers exist in struct dma_map_ops?
>
> Good job snipping the part of my reply which addressed this. Go read
> DMA-API.txt yourself. Carefully.
The snipped part did not contradict your claim that "You're not supposed to use
kmalloc memory for DMA." In the DMA-API.txt document however there are multiple
explicit statements that support allocating memory for DMA with kmalloc(). Here
is one example from the DMA-API.txt section about dma_map_single():
Not all memory regions in a machine can be mapped by this API.
Further, contiguous kernel virtual space may not be contiguous as
physical memory. Since this API does not provide any scatter/gather
capability, it will fail if the user tries to map a non-physically
contiguous piece of memory. For this reason, memory to be mapped by
this API should be obtained from sources which guarantee it to be
physically contiguous (like kmalloc).
Bart.
next prev parent reply other threads:[~2018-09-24 20:54 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
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 [this message]
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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