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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.

  reply	other threads:[~2018-04-27 16:18 UTC|newest]

Thread overview: 34+ 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 19:10         ` Matthew Wilcox
2018-05-03 12:03           ` Michal Hocko
2018-05-03 12:13             ` Christoph Hellwig
2018-04-28 19:46         ` Julia Lawall
2018-04-28 20:41           ` Matthew Wilcox
2018-04-29 14:34             ` Julia Lawall
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
2018-05-10  4:39     ` Yasunari.Takiguchi

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