linux-kernel - Re: [BUG] Devices breaking due to CONFIG_ZONE

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Date:	Sun, 24 Jan 2016 10:40:56 +0100
From:	Borislav Petkov <bp@...e.de>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	Sudip Mukherjee <sudipm.mukherjee@...il.com>,
	Christoph Hellwig <hch@....de>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Jerome Glisse <j.glisse@...il.com>, markk@...ra.co.uk,
	Joerg Roedel <jroedel@...e.de>,
	lkml <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [BUG] Devices breaking due to CONFIG_ZONE_DEVICE

+ linux-mm

On Fri, Jan 22, 2016 at 10:15:17PM -0800, Dan Williams wrote:
> On Fri, Jan 22, 2016 at 9:47 PM, Dan Williams <dan.j.williams@...el.com> wrote:
> > On Fri, Jan 22, 2016 at 8:46 PM, Sudip Mukherjee
> > <sudipm.mukherjee@...il.com> wrote:
> >> Hi All,
> >> Commit 033fbae988fc ("mm: ZONE_DEVICE for "device memory"") has
> >> introduced CONFIG_ZONE_DEVICE while sacrificing CONFIG_ZONE_DMA.
> >> Distributions like Ubuntu has started enabling CONFIG_ZONE_DEVICE and
> >> thus breaking parallel port. Please have a look at
> >> https://bugzilla.kernel.org/show_bug.cgi?id=110931 for the bug report.
> >>
> >> Apart from parallel port I can see some sound drivers will also break.
> >>
> >> Now what is the possible solution for this?
> >
> > The tradeoff here is enabling direct-I/O for persistent memory vs
> > support for legacy devices.
> >
> > One possible solution is to alias ZONE_DMA and ZONE_DEVICE.  At early
> > boot if pmem is detected disable these legacy devices, or the reverse
> > disable DMA to persistent memory if a legacy device is detected.  The
> > latter is a bit harder to do as I think we would want to make the
> > decision early during memory init before we would know if any parallel
> > ports or ISA sound cards are present.
> 
> ...another option that might be cleaner is to teach GFP_DMA to get
> memory from a different mechanism.  I.e. don't use the mm-zone
> infrastructure to organize that small 16MB pool of memory.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--