From: Jerome Glisse <jglisse@redhat.com>
To: Robin Murphy <robin.murphy@arm.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org,
akpm@linux-foundation.org, will.deacon@arm.com,
catalin.marinas@arm.com, mhocko@suse.com,
mgorman@techsingularity.net, james.morse@arm.com,
mark.rutland@arm.com, cpandya@codeaurora.org,
arunks@codeaurora.org, dan.j.williams@intel.com,
osalvador@suse.de, logang@deltatee.com, david@redhat.com,
cai@lca.pw
Subject: Re: [PATCH 6/6] arm64/mm: Enable ZONE_DEVICE
Date: Wed, 3 Apr 2019 12:07:22 -0400 [thread overview]
Message-ID: <20190403160722.GB12818@redhat.com> (raw)
In-Reply-To: <ea5567c7-caad-8a4e-7c6f-cec4b772a526@arm.com>
On Wed, Apr 03, 2019 at 02:58:28PM +0100, Robin Murphy wrote:
> [ +Dan, Jerome ]
>
> On 03/04/2019 05:30, Anshuman Khandual wrote:
> > Arch implementation for functions which create or destroy vmemmap mapping
> > (vmemmap_populate, vmemmap_free) can comprehend and allocate from inside
> > device memory range through driver provided vmem_altmap structure which
> > fulfils all requirements to enable ZONE_DEVICE on the platform. Hence just
>
> ZONE_DEVICE is about more than just altmap support, no?
>
> > enable ZONE_DEVICE by subscribing to ARCH_HAS_ZONE_DEVICE. But this is only
> > applicable for ARM64_4K_PAGES (ARM64_SWAPPER_USES_SECTION_MAPS) only which
> > creates vmemmap section mappings and utilize vmem_altmap structure.
>
> What prevents it from working with other page sizes? One of the foremost
> use-cases for our 52-bit VA/PA support is to enable mapping large quantities
> of persistent memory, so we really do need this for 64K pages too. FWIW, it
> appears not to be an issue for PowerPC.
>
> > Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> > ---
> > arch/arm64/Kconfig | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > index db3e625..b5d8cf5 100644
> > --- a/arch/arm64/Kconfig
> > +++ b/arch/arm64/Kconfig
> > @@ -31,6 +31,7 @@ config ARM64
> > select ARCH_HAS_SYSCALL_WRAPPER
> > select ARCH_HAS_TEARDOWN_DMA_OPS if IOMMU_SUPPORT
> > select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
> > + select ARCH_HAS_ZONE_DEVICE if ARM64_4K_PAGES
>
> IIRC certain configurations (HMM?) don't even build if you just turn this on
> alone (although of course things may have changed elsewhere in the meantime)
> - crucially, though, from previous discussions[1] it seems fundamentally
> unsafe, since I don't think we can guarantee that nobody will touch the
> corners of ZONE_DEVICE that also require pte_devmap in order not to go
> subtly wrong. I did get as far as cooking up some patches to sort that out
> [2][3] which I never got round to posting for their own sake, so please
> consider picking those up as part of this series.
Correct _do not_ enable ZONE_DEVICE without support for pte_devmap detection.
If you want some feature of ZONE_DEVICE. Like HMM as while DAX does require
pte_devmap, HMM device private does not. So you would first have to split
ZONE_DEVICE into more sub-features kconfig option.
What is the end use case you are looking for ? Persistent memory ?
Cheers,
Jérôme
next prev parent reply other threads:[~2019-04-03 16:07 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-03 4:30 [PATCH 0/6] arm64/mm: Enable memory hot remove and ZONE_DEVICE Anshuman Khandual
2019-04-03 4:30 ` [PATCH 1/6] arm64/mm: Enable sysfs based memory hot add interface Anshuman Khandual
2019-04-03 8:20 ` David Hildenbrand
2019-04-03 13:12 ` Robin Murphy
2019-04-04 5:21 ` Anshuman Khandual
2019-04-04 5:25 ` Anshuman Khandual
2019-04-04 8:49 ` David Hildenbrand
2019-04-03 4:30 ` [PATCH 2/6] arm64/mm: Enable memory hot remove Anshuman Khandual
2019-04-03 12:37 ` Robin Murphy
2019-04-03 13:15 ` Steven Price
2019-04-04 6:51 ` Anshuman Khandual
2019-04-04 5:39 ` Anshuman Khandual
2019-04-04 11:58 ` Oscar Salvador
2019-04-04 13:03 ` Anshuman Khandual
2019-04-04 15:19 ` Oscar Salvador
2019-04-03 17:32 ` Logan Gunthorpe
2019-04-03 17:57 ` Robin Murphy
2019-04-04 8:23 ` Anshuman Khandual
2019-04-04 7:07 ` Anshuman Khandual
2019-04-04 9:16 ` Steven Price
2019-04-03 4:30 ` [PATCH 3/6] arm64/mm: Enable struct page allocation from device memory Anshuman Khandual
2019-04-03 4:30 ` [PATCH 4/6] mm/hotplug: Reorder arch_remove_memory() call in __remove_memory() Anshuman Khandual
2019-04-03 8:45 ` Oscar Salvador
2019-04-03 9:17 ` Michal Hocko
2019-04-04 8:32 ` Anshuman Khandual
2019-04-03 9:30 ` David Hildenbrand
2019-04-03 4:30 ` [PATCH 5/6] mm/memremap: Rename and consolidate SECTION_SIZE Anshuman Khandual
2019-04-03 9:26 ` Michal Hocko
2019-04-03 9:30 ` David Hildenbrand
2019-04-03 4:30 ` [PATCH 6/6] arm64/mm: Enable ZONE_DEVICE Anshuman Khandual
2019-04-03 13:58 ` Robin Murphy
2019-04-03 16:07 ` Jerome Glisse [this message]
2019-04-04 5:03 ` Anshuman Khandual
2019-04-04 4:42 ` Anshuman Khandual
2019-04-04 5:04 ` Dan Williams
2019-04-04 9:46 ` Robin Murphy
2019-04-07 22:11 ` Dan Williams
2019-04-08 4:03 ` Ira Weiny
2019-04-08 6:03 ` Anshuman Khandual
2019-04-03 18:08 ` [PATCH 0/6] arm64/mm: Enable memory hot remove and ZONE_DEVICE Dan Williams
2019-04-04 13:11 ` Anshuman Khandual
2019-04-04 9:46 ` [RFC 1/2] mm/vmemmap: Enable vmem_altmap based base page mapping for vmemmap Anshuman Khandual
2019-04-04 9:46 ` [RFC 2/2] arm64/mm: Enable ZONE_DEVICE for all page configs Anshuman Khandual
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