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From: Christoph Hellwig <hch@lst.de>
To: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Baoquan He <bhe@redhat.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	akpm@linux-foundation.org, hch@lst.de, 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: Tue, 21 Dec 2021 09:56:23 +0100	[thread overview]
Message-ID: <20211221085623.GA7733@lst.de> (raw)
In-Reply-To: <Ybx2szXEgl1tN4MD@ip-172-31-30-232.ap-northeast-1.compute.internal>

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.

> 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.


  reply	other threads:[~2021-12-21  8:56 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 [this message]
2021-12-22 12:37           ` Hyeonggon Yoo
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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