From: Xishi Qiu <qiuxishi@gmail.com>
To: Dan Williams <dan.j.williams@intel.com>,
Dave Hansen <dave.hansen@linux.intel.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Dave Jiang <dave.jiang@intel.com>,
zwisler@kernel.org, Vishal L Verma <vishal.l.verma@intel.com>,
Tom Lendacky <thomas.lendacky@amd.com>,
Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@suse.com>,
linux-nvdimm <linux-nvdimm@lists.01.org>,
Linux MM <linux-mm@kvack.org>,
"Huang, Ying" <ying.huang@intel.com>,
Fengguang Wu <fengguang.wu@intel.com>,
Xishi Qiu <qiuxishi@linux.alibaba.com>,
zy107165@alibaba-inc.com
Subject: Re: [PATCH 0/9] Allow persistent memory to be used like normal RAM
Date: Fri, 26 Oct 2018 16:03:38 +0800 [thread overview]
Message-ID: <352acc87-a6da-65e4-bbe6-0dbffdc72acc@gmail.com> (raw)
In-Reply-To: <CAPcyv4hFoPkda0YfNKo=nFxttyBG3OjD7vKWyNzLY+8T5gLc=g@mail.gmail.com>
Hi Dan,
How about let the BIOS report a new type for kmem in e820 table?
e.g.
#define E820_PMEM 7
#define E820_KMEM 8
Then pmem and kmem are separately, and we can easily hotadd kmem
to the memory subsystem, no disturb the existing code (e.g. pmem,
nvdimm, dax...).
I don't know whether Intel will change some hardware features for
pmem which used like a volatility memory in the future. Perhaps
faster than pmem, cheaper, but volatility, and no need to care
about atomicity, consistency, L2/L3 cache...
Another question, why call it kmem? what does the "k" mean?
Thanks,
Xishi Qiu
On 2018/10/23 09:11, Dan Williams wrote:
> On Mon, Oct 22, 2018 at 6:05 PM Dan Williams <dan.j.williams@intel.com> wrote:
>>
>> On Mon, Oct 22, 2018 at 1:18 PM Dave Hansen <dave.hansen@linux.intel.com> wrote:
>>>
>>> Persistent memory is cool. But, currently, you have to rewrite
>>> your applications to use it. Wouldn't it be cool if you could
>>> just have it show up in your system like normal RAM and get to
>>> it like a slow blob of memory? Well... have I got the patch
>>> series for you!
>>>
>>> This series adds a new "driver" to which pmem devices can be
>>> attached. Once attached, the memory "owned" by the device is
>>> hot-added to the kernel and managed like any other memory. On
>>> systems with an HMAT (a new ACPI table), each socket (roughly)
>>> will have a separate NUMA node for its persistent memory so
>>> this newly-added memory can be selected by its unique NUMA
>>> node.
>>>
>>> This is highly RFC, and I really want the feedback from the
>>> nvdimm/pmem folks about whether this is a viable long-term
>>> perversion of their code and device mode. It's insufficiently
>>> documented and probably not bisectable either.
>>>
>>> Todo:
>>> 1. The device re-binding hacks are ham-fisted at best. We
>>> need a better way of doing this, especially so the kmem
>>> driver does not get in the way of normal pmem devices.
>>> 2. When the device has no proper node, we default it to
>>> NUMA node 0. Is that OK?
>>> 3. We muck with the 'struct resource' code quite a bit. It
>>> definitely needs a once-over from folks more familiar
>>> with it than I.
>>> 4. Is there a better way to do this than starting with a
>>> copy of pmem.c?
>>
>> So I don't think we want to do patch 2, 3, or 5. Just jump to patch 7
>> and remove all the devm_memremap_pages() infrastructure and dax_region
>> infrastructure.
>>
>> The driver should be a dead simple turn around to call add_memory()
>> for the passed in range. The hard part is, as you say, arranging for
>> the kmem driver to not stand in the way of typical range / device
>> claims by the dax_pmem device.
>>
>> To me this looks like teaching the nvdimm-bus and this dax_kmem driver
>> to require explicit matching based on 'id'. The attachment scheme
>> would look like this:
>>
>> modprobe dax_kmem
>> echo dax0.0 > /sys/bus/nd/drivers/dax_kmem/new_id
>> echo dax0.0 > /sys/bus/nd/drivers/dax_pmem/unbind
>> echo dax0.0 > /sys/bus/nd/drivers/dax_kmem/bind
>>
>> At step1 the dax_kmem drivers will match no devices and stays out of
>> the way of dax_pmem. It learns about devices it cares about by being
>> explicitly told about them. Then unbind from the typical dax_pmem
>> driver and attach to dax_kmem to perform the one way hotplug.
>>
>> I expect udev can automate this by setting up a rule to watch for
>> device-dax instances by UUID and call a script to do the detach /
>> reattach dance.
>
> The next question is how to support this for ranges that don't
> originate from the pmem sub-system. I expect we want dax_kmem to
> register a generic platform device representing the range and have a
> generic platofrm driver that turns around and does the add_memory().
>
next prev parent reply other threads:[~2018-10-26 8:04 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-22 20:13 [PATCH 0/9] Allow persistent memory to be used like normal RAM Dave Hansen
2018-10-22 20:13 ` [PATCH 1/9] mm/resource: return real error codes from walk failures Dave Hansen
2018-10-22 20:13 ` [PATCH 2/9] dax: kernel memory driver for mm ownership of DAX Dave Hansen
2018-10-23 1:56 ` Randy Dunlap
2018-10-22 20:13 ` [PATCH 3/9] dax: add more kmem device infrastructure Dave Hansen
2018-10-22 20:13 ` [PATCH 4/9] dax/kmem: allow PMEM devices to bind to KMEM driver Dave Hansen
2018-10-22 20:13 ` [PATCH 5/9] dax/kmem: add more nd dax kmem infrastructure Dave Hansen
2018-10-22 20:13 ` [PATCH 6/9] mm/memory-hotplug: allow memory resources to be children Dave Hansen
2018-10-22 20:13 ` [PATCH 7/9] dax/kmem: actually perform memory hotplug Dave Hansen
2018-10-22 20:13 ` [PATCH 8/9] dax/kmem: let walk_system_ram_range() search child resources Dave Hansen
2018-10-22 20:13 ` [PATCH 9/9] dax/kmem: actually enable the code in Makefile Dave Hansen
2018-10-23 1:05 ` [PATCH 0/9] Allow persistent memory to be used like normal RAM Dan Williams
2018-10-23 1:11 ` Dan Williams
2018-10-26 8:03 ` Xishi Qiu [this message]
2018-10-26 13:58 ` Dave Hansen
2018-10-27 4:45 ` Dan Williams
2018-10-23 18:12 ` Elliott, Robert (Persistent Memory)
2018-10-23 18:16 ` Dave Hansen
2018-10-23 18:58 ` Dan Williams
2018-10-26 5:42 ` Xishi Qiu
2018-10-26 9:03 ` Fengguang Wu
2018-10-27 11:00 ` Fengguang Wu
2018-10-31 5:11 ` Yang Shi
2018-12-03 9:22 ` Brice Goglin
2018-12-03 16:56 ` Dave Hansen
2018-12-03 17:16 ` Dan Williams
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