From: Hyeonggon Yoo <42.hyeyoo@gmail.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Baoquan He <bhe@redhat.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
akpm@linux-foundation.org, cl@linux.com,
John.p.donnelly@oracle.com, kexec@lists.infradead.org,
stable@vger.kernel.org, Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Vlastimil Babka <vbabka@suse.cz>
Subject: Re: [PATCH v3 5/5] mm/slub: do not create dma-kmalloc if no managed pages in DMA zone
Date: Wed, 22 Dec 2021 12:37:03 +0000 [thread overview]
Message-ID: <YcMb7+RESj1nEx9l@ip-172-31-30-232.ap-northeast-1.compute.internal> (raw)
In-Reply-To: <20211221085623.GA7733@lst.de>
Hello Christoph.
On Tue, Dec 21, 2021 at 09:56:23AM +0100, Christoph Hellwig wrote:
> On Fri, Dec 17, 2021 at 11:38:27AM +0000, Hyeonggon Yoo wrote:
> > My understanding is any buffer requested from kmalloc (without
> > GFP_DMA/DMA32) can be used by device driver because it allocates
> > continuous physical memory. It doesn't mean that buffer allocated
> > with kmalloc is free of addressing limitation.
>
> Yes.
>
> >
> > the addressing limitation comes from the capability of device, not
> > allocation size. if you allocate memory using alloc_pages() or kmalloc(),
> > the device has same limitation. and vmalloc can't be used for
> > devices because they have no MMU.
>
> vmalloc can be used as well, it just needs to be setup as a scatterlist
> and needs a little lover for DMA challenged platforms with the
> invalidate_kernel_vmap_range and flush_kernel_vmap_range helpers.
Oh I misunderstood this. Underlying physical address of vmalloc()-allocated memory
can be mapped using DMA API, and it needs to be setup as scatterlist because
the allocated memory is not physically continuous. Right?
BTW, looking at the API I think the scsi case can be converted to use
dma_alloc_pages(). but driver requires 512 bytes of buffer and the API
supports allocating by at least page size.
It's not a big problem as it allocates a single buffer but in other
cases maybe not. Can't we use dma pool for non-coherent pages?
Thanks,
Hyeonggon.
> > But we can map memory outside DMA zone into bounce buffer (which resides
> > in DMA zone) using DMA API.
>
> Yes, although in a few specific cases the bounce buffer could also come
> from somewhere else.
next prev parent reply other threads:[~2021-12-22 12:37 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20211213122712.23805-1-bhe@redhat.com>
2021-12-13 12:27 ` [PATCH v3 3/5] mm_zone: add function to check if managed dma zone exists Baoquan He
2021-12-13 14:22 ` john.p.donnelly
2021-12-16 10:52 ` David Hildenbrand
2021-12-13 12:27 ` [PATCH v3 4/5] dma/pool: create dma atomic pool only if dma zone has managed pages Baoquan He
2021-12-13 14:23 ` john.p.donnelly
2021-12-13 12:27 ` [PATCH v3 5/5] mm/slub: do not create dma-kmalloc if no managed pages in DMA zone Baoquan He
2021-12-13 13:43 ` Hyeonggon Yoo
2021-12-14 5:32 ` Baoquan He
2021-12-14 10:09 ` Vlastimil Babka
2021-12-14 10:28 ` Christoph Lameter
2021-12-15 4:48 ` Hyeonggon Yoo
2021-12-15 7:03 ` Hyeonggon Yoo
2021-12-15 7:27 ` Christoph Hellwig
2021-12-15 10:34 ` Vlastimil Babka
2021-12-15 11:51 ` David Laight
2021-12-15 13:41 ` Baoquan He
2021-12-17 11:38 ` Hyeonggon Yoo
2021-12-20 7:32 ` Baoquan He
2022-01-07 11:56 ` Hyeonggon Yoo
2021-12-15 14:42 ` Baoquan He
2021-12-15 10:08 ` Baoquan He
2021-12-17 11:38 ` Hyeonggon Yoo
2021-12-21 8:56 ` Christoph Hellwig
2021-12-22 12:37 ` Hyeonggon Yoo [this message]
2021-12-23 8:52 ` Christoph Hellwig
2021-12-13 14:24 ` john.p.donnelly
2021-12-14 16:31 ` Christoph Hellwig
2021-12-14 17:07 ` john.p.donnelly
2021-12-15 7:27 ` Christoph Hellwig
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