From: "Jan Beulich" <JBeulich@suse.com>
To: Haozhong Zhang <haozhong.zhang@intel.com>
Cc: Juergen Gross <JGross@suse.com>,
Kevin Tian <kevin.tian@intel.com>, Wei Liu <wei.liu2@citrix.com>,
Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
George Dunlap <George.Dunlap@eu.citrix.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Ian Jackson <Ian.Jackson@eu.citrix.com>,
George Dunlap <george.dunlap@citrix.com>,
"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>,
Jun Nakajima <jun.nakajima@intel.com>,
Xiao Guangrong <guangrong.xiao@linux.intel.com>,
Keir Fraser <keir@xen.org>
Subject: Re: [RFC Design Doc] Add vNVDIMM support for Xen
Date: Fri, 22 Apr 2016 02:24:36 -0600 [thread overview]
Message-ID: <5719FBE402000078000E48FC@prv-mh.provo.novell.com> (raw)
In-Reply-To: <20160422023606.GA5975@hz-desktop.sh.intel.com>
>>> On 22.04.16 at 04:36, <haozhong.zhang@intel.com> wrote:
> On 04/21/16 01:04, Jan Beulich wrote:
>> >>> On 21.04.16 at 07:09, <haozhong.zhang@intel.com> wrote:
>> > On 04/12/16 16:45, Haozhong Zhang wrote:
>> >> On 04/08/16 09:52, Jan Beulich wrote:
>> >> > >>> On 08.04.16 at 07:02, <haozhong.zhang@intel.com> wrote:
>> >> > > On 03/29/16 04:49, Jan Beulich wrote:
>> >> > >> >>> On 29.03.16 at 12:10, <haozhong.zhang@intel.com> wrote:
>> >> > >> > On 03/29/16 03:11, Jan Beulich wrote:
>> >> > >> >> >>> On 29.03.16 at 10:47, <haozhong.zhang@intel.com> wrote:
>> >> > > [..]
>> >> > >> >> > I still cannot find a neat approach to manage guest permissions for
>> >> > >> >> > nvdimm pages. A possible one is to use a per-domain bitmap to track
>> >> > >> >> > permissions: each bit corresponding to an nvdimm page. The bitmap can
>> >> > >> >> > save lots of spaces and even be stored in the normal ram, but
>> >> > >> >> > operating it for a large nvdimm range, especially for a contiguous
>> >> > >> >> > one, is slower than rangeset.
>> >> > >> >>
>> >> > >> >> I don't follow: What would a single bit in that bitmap mean? Any
>> >> > >> >> guest may access the page? That surely wouldn't be what we
>> >> > >> >> need.
>> >> > >> >>
>> >> > >> >
>> >> > >> > For a host having a N pages of nvdimm, each domain will have a N bits
>> >> > >> > bitmap. If the m'th bit of a domain's bitmap is set, then that domain
>> >> > >> > has the permission to access the m'th host nvdimm page.
>> >> > >>
>> >> > >> Which will be more overhead as soon as there are enough such
>> >> > >> domains in a system.
>> >> > >>
>> >> > >
>> >> > > Sorry for the late reply.
>> >> > >
>> >> > > I think we can make some optimization to reduce the space consumed by
>> >> > > the bitmap.
>> >> > >
>> >> > > A per-domain bitmap covering the entire host NVDIMM address range is
>> >> > > wasteful especially if the actual used ranges are congregated. We may
>> >> > > take following ways to reduce its space.
>> >> > >
>> >> > > 1) Split the per-domain bitmap into multiple sub-bitmap and each
>> >> > > sub-bitmap covers a smaller and contiguous sub host NVDIMM address
>> >> > > range. In the beginning, no sub-bitmap is allocated for the
>> >> > > domain. If the access permission to a host NVDIMM page in a sub
>> >> > > host address range is added to a domain, only the sub-bitmap for
>> >> > > that address range is allocated for the domain. If access
>> >> > > permissions to all host NVDIMM pages in a sub range are removed
>> >> > > from a domain, the corresponding sub-bitmap can be freed.
>> >> > >
>> >> > > 2) If a domain has access permissions to all host NVDIMM pages in a
>> >> > > sub range, the corresponding sub-bitmap will be replaced by a range
>> >> > > struct. If range structs are used to track adjacent ranges, they
>> >> > > will be merged into one range struct. If access permissions to some
>> >> > > pages in that sub range are removed from a domain, the range struct
>> >> > > should be converted back to bitmap segment(s).
>> >> > >
>> >> > > 3) Because there might be lots of above bitmap segments and range
>> >> > > structs per-domain, we can organize them in a balanced interval
>> >> > > tree to quickly search/add/remove an individual structure.
>> >> > >
>> >> > > In the worst case that each sub range has non-contiguous pages
>> >> > > assigned to a domain, above solution will use all sub-bitmaps and
>> >> > > consume more space than a single bitmap because of the extra space for
>> >> > > organization. I assume that the sysadmin should be responsible to
>> >> > > ensure the host nvdimm ranges assigned to each domain as contiguous
>> >> > > and congregated as possible in order to avoid the worst case. However,
>> >> > > if the worst case does happen, xen hypervisor should refuse to assign
>> >> > > nvdimm to guest when it runs out of memory.
>> >> >
>> >> > To be honest, this all sounds pretty unconvincing wrt not using
>> >> > existing code paths - a lot of special treatment, and hence a lot
>> >> > of things that can go (slightly) wrong.
>> >> >
>> >>
>> >> Well, using existing range struct to manage guest access permissions
>> >> to nvdimm could consume too much space which could not fit in either
>> >> memory or nvdimm. If the above solution looks really error-prone,
>> >> perhaps we can still come back to the existing one and restrict the
>> >> number of range structs each domain could have for nvdimm
>> >> (e.g. reserve one 4K-page per-domain for them) to make it work for
>> >> nvdimm, though it may reject nvdimm mapping that is terribly
>> >> fragmented.
>> >
>> > Hi Jan,
>> >
>> > Any comments for this?
>>
>> Well, nothing new, i.e. my previous opinion on the old proposal didn't
>> change. I'm really opposed to any artificial limitations here, as I am to
>> any secondary (and hence error prone) code paths. IOW I continue
>> to think that there's no reasonable alternative to re-using the existing
>> memory management infrastructure for at least the PMEM case.
>
> By re-using the existing memory management infrastructure, do you mean
> re-using the existing model of MMIO for passthrough PCI devices to
> handle the permission of pmem?
No, re-using struct page_info.
>> The
>> only open question remains to be where to place the control structures,
>> and I think the thresholding proposal of yours was quite sensible.
>
> I'm little confused here. Is 'restrict the number of range structs' in
> my previous reply the 'thresholding proposal' you mean? Or it's one of
> 'artificial limitations'?
Neither. It's the decision on where to place the struct page_info
arrays needed to manage the PMEM ranges.
Jan
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next prev parent reply other threads:[~2016-04-22 8:24 UTC|newest]
Thread overview: 121+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-01 5:44 [RFC Design Doc] Add vNVDIMM support for Xen Haozhong Zhang
2016-02-01 18:25 ` Andrew Cooper
2016-02-02 3:27 ` Tian, Kevin
2016-02-02 3:44 ` Haozhong Zhang
2016-02-02 11:09 ` Andrew Cooper
2016-02-02 6:33 ` Tian, Kevin
2016-02-02 7:39 ` Zhang, Haozhong
2016-02-02 7:48 ` Tian, Kevin
2016-02-02 7:53 ` Zhang, Haozhong
2016-02-02 8:03 ` Tian, Kevin
2016-02-02 8:49 ` Zhang, Haozhong
2016-02-02 19:01 ` Konrad Rzeszutek Wilk
2016-02-02 17:11 ` Stefano Stabellini
2016-02-03 7:00 ` Haozhong Zhang
2016-02-03 9:13 ` Jan Beulich
2016-02-03 14:09 ` Andrew Cooper
2016-02-03 14:23 ` Haozhong Zhang
2016-02-05 14:40 ` Ross Philipson
2016-02-06 1:43 ` Haozhong Zhang
2016-02-06 16:17 ` Ross Philipson
2016-02-03 12:02 ` Stefano Stabellini
2016-02-03 13:11 ` Haozhong Zhang
2016-02-03 14:20 ` Andrew Cooper
2016-02-04 3:10 ` Haozhong Zhang
2016-02-03 15:16 ` George Dunlap
2016-02-03 15:22 ` Stefano Stabellini
2016-02-03 15:35 ` Konrad Rzeszutek Wilk
2016-02-03 15:35 ` George Dunlap
2016-02-04 2:55 ` Haozhong Zhang
2016-02-04 12:24 ` Stefano Stabellini
2016-02-15 3:16 ` Zhang, Haozhong
2016-02-16 11:14 ` Stefano Stabellini
2016-02-16 12:55 ` Jan Beulich
2016-02-17 9:03 ` Haozhong Zhang
2016-03-04 7:30 ` Haozhong Zhang
2016-03-16 12:55 ` Haozhong Zhang
2016-03-16 13:13 ` Konrad Rzeszutek Wilk
2016-03-16 13:16 ` Jan Beulich
2016-03-16 13:55 ` Haozhong Zhang
2016-03-16 14:23 ` Jan Beulich
2016-03-16 14:55 ` Haozhong Zhang
2016-03-16 15:23 ` Jan Beulich
2016-03-17 8:58 ` Haozhong Zhang
2016-03-17 11:04 ` Jan Beulich
2016-03-17 12:44 ` Haozhong Zhang
2016-03-17 12:59 ` Jan Beulich
2016-03-17 13:29 ` Haozhong Zhang
2016-03-17 13:52 ` Jan Beulich
2016-03-17 14:00 ` Ian Jackson
2016-03-17 14:21 ` Haozhong Zhang
2016-03-29 8:47 ` Haozhong Zhang
2016-03-29 9:11 ` Jan Beulich
2016-03-29 10:10 ` Haozhong Zhang
2016-03-29 10:49 ` Jan Beulich
2016-04-08 5:02 ` Haozhong Zhang
2016-04-08 15:52 ` Jan Beulich
2016-04-12 8:45 ` Haozhong Zhang
2016-04-21 5:09 ` Haozhong Zhang
2016-04-21 7:04 ` Jan Beulich
2016-04-22 2:36 ` Haozhong Zhang
2016-04-22 8:24 ` Jan Beulich [this message]
2016-04-22 10:16 ` Haozhong Zhang
2016-04-22 10:53 ` Jan Beulich
2016-04-22 12:26 ` Haozhong Zhang
2016-04-22 12:36 ` Jan Beulich
2016-04-22 12:54 ` Haozhong Zhang
2016-04-22 13:22 ` Jan Beulich
2016-03-17 13:32 ` Konrad Rzeszutek Wilk
2016-02-03 15:47 ` Konrad Rzeszutek Wilk
2016-02-04 2:36 ` Haozhong Zhang
2016-02-15 9:04 ` Zhang, Haozhong
2016-02-02 19:15 ` Konrad Rzeszutek Wilk
2016-02-03 8:28 ` Haozhong Zhang
2016-02-03 9:18 ` Jan Beulich
2016-02-03 12:22 ` Haozhong Zhang
2016-02-03 12:38 ` Jan Beulich
2016-02-03 12:49 ` Haozhong Zhang
2016-02-03 14:30 ` Andrew Cooper
2016-02-03 14:39 ` Jan Beulich
2016-02-15 8:43 ` Haozhong Zhang
2016-02-15 11:07 ` Jan Beulich
2016-02-17 9:01 ` Haozhong Zhang
2016-02-17 9:08 ` Jan Beulich
2016-02-18 7:42 ` Haozhong Zhang
2016-02-19 2:14 ` Konrad Rzeszutek Wilk
2016-03-01 7:39 ` Haozhong Zhang
2016-03-01 18:33 ` Ian Jackson
2016-03-01 18:49 ` Konrad Rzeszutek Wilk
2016-03-02 7:14 ` Haozhong Zhang
2016-03-02 13:03 ` Jan Beulich
2016-03-04 2:20 ` Haozhong Zhang
2016-03-08 9:15 ` Haozhong Zhang
2016-03-08 9:27 ` Jan Beulich
2016-03-09 12:22 ` Haozhong Zhang
2016-03-09 16:17 ` Jan Beulich
2016-03-10 3:27 ` Haozhong Zhang
2016-03-17 11:05 ` Ian Jackson
2016-03-17 13:37 ` Haozhong Zhang
2016-03-17 13:56 ` Jan Beulich
2016-03-17 14:22 ` Haozhong Zhang
2016-03-17 14:12 ` Xu, Quan
2016-03-17 14:22 ` Zhang, Haozhong
2016-03-07 20:53 ` Konrad Rzeszutek Wilk
2016-03-08 5:50 ` Haozhong Zhang
2016-02-18 17:17 ` Jan Beulich
2016-02-24 13:28 ` Haozhong Zhang
2016-02-24 14:00 ` Ross Philipson
2016-02-24 16:42 ` Haozhong Zhang
2016-02-24 17:50 ` Ross Philipson
2016-02-24 14:24 ` Jan Beulich
2016-02-24 15:48 ` Haozhong Zhang
2016-02-24 16:54 ` Jan Beulich
2016-02-28 14:48 ` Haozhong Zhang
2016-02-29 9:01 ` Jan Beulich
2016-02-29 9:45 ` Haozhong Zhang
2016-02-29 10:12 ` Jan Beulich
2016-02-29 11:52 ` Haozhong Zhang
2016-02-29 12:04 ` Jan Beulich
2016-02-29 12:22 ` Haozhong Zhang
2016-03-01 13:51 ` Ian Jackson
2016-03-01 15:04 ` Jan Beulich
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