Re: [RFC PATCH] mm: support CONFIG_ZONE_DEVICE + CONFIG_ZONE_DMA

["Mark" <markk@clara.co.uk>]

On Tue, January 26, 2016 06:00, Sudip Mukherjee wrote:
> On Mon, Jan 25, 2016 at 04:06:40PM -0800, Dan Williams wrote:
>> It appears devices requiring ZONE_DMA are still prevalent (see link
>> below).  For this reason the proposal to require turning off ZONE_DMA to
>> enable ZONE_DEVICE is untenable in the short term.  We want a single
>> kernel image to be able to support legacy devices as well as next
>> generation persistent memory platforms.
>>
>> Towards this end, alias ZONE_DMA and ZONE_DEVICE to work around needing
>> to maintain a unique zone number for ZONE_DEVICE.  Record the geometry
>> of ZONE_DMA at init (->init_spanned_pages) and use that information in
>> is_zone_device_page() to differentiate pages allocated via
>> devm_memremap_pages() vs true ZONE_DMA pages.  Otherwise, use the
>> simpler definition of is_zone_device_page() when ZONE_DMA is turned off.
>>
>> Note that this also teaches the memory hot remove path that the zone may
>> not have sections for all pfn spans (->zone_dyn_start_pfn).
>>
>> A user visible implication of this change is potentially an unexpectedly
>> high "spanned" value in /proc/zoneinfo for the DMA zone.
>>
>> Cc: H. Peter Anvin <hpa@zytor.com>
>> Cc: Ingo Molnar <mingo@redhat.com>
>> Cc: Rik van Riel <riel@redhat.com>
>> Cc: Mel Gorman <mgorman@suse.de>
>> Cc: Jerome Glisse <j.glisse@gmail.com>
>> Cc: Christoph Hellwig <hch@lst.de>
>> Cc: Dave Hansen <dave.hansen@linux.intel.com>
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=110931
>> Fixes: 033fbae988fc ("mm: ZONE_DEVICE for "device memory"")
>> Reported-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
>
> It should actually be Reported-by: Mark <markk@clara.co.uk>
>
> Hi Mark,
> Can you please test this patch available at
> https://patchwork.kernel.org/patch/8116991/
> in your setup..

I applied that patch to 4.5-rc1 and it seems to work. At least, there is
no error message in dmesg output any more. I didn't actually try using the
parallel port (need to find a parallel printer cable). Presumably a
parallel printer would work whether DMA is used or not, just slower and
using more CPU time in the PIO case. Also, I don't have any hardware that
needs CONFIG_ZONE_DEVICE.

The config file I used to compile the kernel can be downloaded from
https://www.mediafire.com/?1do33bkko41ypo3
if anyone feels like taking a look.

Perhaps someone with one of the affected PCI sound cards could also test
the patch, since those presumably don't work/build at all without it.
Hopefully someone else has a PC with native parallel port to confirm the
fix. (Native floppy controller may be another affected device.)


Mark


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