From: Dan Williams <dan.j.williams@intel.com>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Rik van Riel <riel@redhat.com>,
"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Christoph Hellwig <hch@lst.de>, Linux MM <linux-mm@kvack.org>,
Ingo Molnar <mingo@redhat.com>, Mel Gorman <mgorman@suse.de>,
"H. Peter Anvin" <hpa@zytor.com>,
Jerome Glisse <j.glisse@gmail.com>,
Sudip Mukherjee <sudipm.mukherjee@gmail.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Laura Abbott <labbott@fedoraproject.org>
Subject: Re: [RFC PATCH] mm: support CONFIG_ZONE_DEVICE + CONFIG_ZONE_DMA
Date: Tue, 26 Jan 2016 13:48:14 -0800 [thread overview]
Message-ID: <CAPcyv4iQHDXw9ah7fOqEjHGCVpnLAyyx+KWNTdQ-vCzAEk7GgA@mail.gmail.com> (raw)
In-Reply-To: <56A7E846.30607@suse.cz>
On Tue, Jan 26, 2016 at 1:42 PM, Vlastimil Babka <vbabka@suse.cz> wrote:
> On 26.1.2016 1:06, 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 Joonsoo, Laura]
>
> Sounds like quite a hack :(
Indeed...
> Would it be possible to extend the bits encoding
> zone? Potentially, ZONE_CMA could be added one day...
Not without impacting the ability to quickly lookup the numa node and
parent section for a page. See ZONES_WIDTH, NODES_WIDTH, and
SECTIONS_WIDTH.
My initial implementation of ZONE_DEVICE ran into this conflict when
ZONES_SHIFT is > 2, and I fell back to cannibalizing ZONE_DMA.
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next prev parent reply other threads:[~2016-01-26 21:48 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-26 0:06 Dan Williams
2016-01-26 6:00 ` Sudip Mukherjee
2016-01-26 17:07 ` Dan Williams
2016-01-26 19:10 ` Mark
2016-01-26 21:42 ` Vlastimil Babka
2016-01-26 21:48 ` Dan Williams [this message]
2016-01-26 22:11 ` Andrew Morton
2016-01-26 22:33 ` Dan Williams
2016-01-26 22:51 ` Andrew Morton
2016-01-26 23:11 ` Dan Williams
2016-01-27 1:18 ` Joonsoo Kim
2016-01-27 1:37 ` Dan Williams
2016-01-27 2:15 ` Joonsoo Kim
2016-01-27 3:23 ` Dan Williams
2016-01-27 3:52 ` Joonsoo Kim
2016-01-27 4:26 ` Dan Williams
2016-01-27 5:52 ` Joonsoo Kim
2016-01-27 7:46 ` Mel Gorman
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