From: Matthew Wilcox <willy@infradead.org>
To: Christopher Lameter <cl@linux.com>
Cc: Michal Hocko <mhocko@kernel.org>,
Christoph Hellwig <hch@infradead.org>,
"Luis R. Rodriguez" <mcgrof@kernel.org>,
linux-mm@kvack.org, Jan Kara <jack@suse.cz>,
matthew@wil.cx, x86@kernel.org, luto@amacapital.net,
martin.petersen@oracle.com, jthumshirn@suse.de,
broonie@kernel.org, linux-spi@vger.kernel.org,
linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org,
"lsf-pc@lists.linux-foundation.org"
<lsf-pc@lists.linux-foundation.org>
Subject: Re: [LSF/MM TOPIC NOTES] x86 ZONE_DMA love
Date: Fri, 27 Apr 2018 09:18:13 -0700 [thread overview]
Message-ID: <20180427161813.GD8161@bombadil.infradead.org> (raw)
In-Reply-To: <alpine.DEB.2.20.1804271103160.11686@nuc-kabylake>
On Fri, Apr 27, 2018 at 11:07:07AM -0500, Christopher Lameter wrote:
> Well it looks like what we are using it for is to force allocation from
> low physical memory if we fail to obtain proper memory through a normal
> channel. The use of ZONE_DMA is only there for emergency purposes.
> I think we could subsitute ZONE_DMA32 on x87 without a problem.
>
> Which means that ZONE_DMA has no purpose anymore.
>
> Can we make ZONE_DMA on x86 refer to the low 32 bit physical addresses
> instead and remove ZONE_DMA32?
>
> That would actually improve the fallback because you have more memory for
> the old devices.
Some devices have incredibly bogus hardware like 28 bit addressing
or 39 bit addressing. We don't have a good way to allocate memory by
physical address other than than saying "GFP_DMA for anything less than
32, GFP_DMA32 (or GFP_KERNEL on 32-bit) for anything less than 64 bit".
Even CMA doesn't have a "cma_alloc_phys()". Maybe that's the right place
to put such an allocation API.
next prev parent reply other threads:[~2018-04-27 16:18 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-26 21:54 [LSF/MM TOPIC NOTES] x86 ZONE_DMA love Luis R. Rodriguez
2018-04-27 1:09 ` [Lsf-pc] " Rik van Riel
2018-04-27 5:35 ` Christoph Hellwig
2018-04-27 7:18 ` Michal Hocko
2018-04-27 16:07 ` Christopher Lameter
2018-04-27 16:18 ` Matthew Wilcox [this message]
2018-04-27 16:36 ` Christopher Lameter
2018-04-28 8:33 ` Christoph Hellwig
2018-04-27 16:37 ` Michal Hocko
2018-04-28 8:33 ` Christoph Hellwig
2018-04-28 8:30 ` Christoph Hellwig
2018-04-27 16:14 ` Luis R. Rodriguez
2018-04-27 16:28 ` Matthew Wilcox
2018-04-28 8:42 ` Christoph Hellwig
2018-04-28 18:55 ` Luis R. Rodriguez
2018-04-28 19:46 ` Julia Lawall
2018-04-28 20:41 ` Matthew Wilcox
2018-04-29 14:34 ` Julia Lawall
[not found] ` <CAFhKne8u7KcBkpgiQ0fFZyh5_EorfY-_MJJaEYk3feCOd9LsRQ@mail.gmail.com>
2018-05-03 12:03 ` Michal Hocko
2018-05-03 12:13 ` Christoph Hellwig
2018-05-03 8:20 ` Geert Uytterhoeven
2018-05-05 16:08 ` Are media drivers abusing of GFP_DMA? - was: " Mauro Carvalho Chehab
2018-05-07 13:26 ` Laurent Pinchart
2018-05-07 15:19 ` Mauro Carvalho Chehab
2018-05-14 8:00 ` Fabien DESSENNE
2018-05-14 10:35 ` Mauro Carvalho Chehab
2018-05-14 10:39 ` Mauro Carvalho Chehab
2018-05-15 7:30 ` Fabien DESSENNE
2018-05-15 8:27 ` Laurent Pinchart
2018-05-15 10:30 ` Mauro Carvalho Chehab
2018-05-15 16:24 ` Luis R. Rodriguez
2018-05-10 4:39 ` Yasunari.Takiguchi
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