Tim Deegan <mailto:Tim.Deegan@xxxxxxxxxx> wrote:
> At 03:54 -0500 on 09 Feb (1234151686), Jiang, Yunhong wrote:
>> Hi, Tim, this patchset try to support page offline request.
> I want to get some initial feedback before more testing.
>
> I haven't had a chance to read the patches in detail yet, but
> my initial
> impression is that:
Thanks for your comments very much!
>
> - The general approach so far seems good (I suspect that your
> 2.3 stage
> below could also be done like 2.2 without a full live migration but
> since that's not implemented yet that's fine).
Yes, for HVM guest, if it has stub domain support, we can do it through two
step:
a) first do the update for the stub domain as 2.2
b) update the shadow/hap page table for the domain itself.
But as stub domain support is not official enabled, so we will wait till stub
domain is by default enabled.
> - It seems like a lot of code for what it does. On the Xen
> side that's
> just a general impression since I'm not familiar with the
> bits of the
For Xen part, the reason is because the currently heap allocator is based on
buddy system, while the offlined page may be in the middle of the buddy, so we
have to split the original buddy into several smaller one.
And do you mean I need turn to Keir for the heap allocator changes?
> heap allocators that you're changing. In libxc you seem to have
> duplicated parts of the save/restore code -- better to make those
> routines externally visible to the rest of libxc and call them from
> your new function. - Like all systems code everywhere, it needs more
> comments. :) You've introduced some generic-sounding functions
> (adjust_pte &c) without describing what they do.
Yes, I will add it in next round.
-- Yunhong
>
> I'll have more detailed comments later in the week, I hope.
>
> Cheers,
>
> Tim.
>
>> Page offline can be used by multiple usage model, belows are some examples:
>> a) If too many correctable error happen to one page,
> management tools may try to offline the page to avoid more
> server error in future;
>> b) When page is ECC error and can't be recoverd by hardware,
> Xen's MCA handler may try to offline the page, so that it will
> not be accessed anymore.
>> c) Offline some DIMM for power management etc (Of course,
> this is far more than simple page offline)
>>
>> The basic idea to offline a page is:
>> 1) If a page is free, it will be removed from page allocator
>> 2) If page is in use, the owner will be checked
>> 2.1) if it is owned by xen/dom0, the offline will be failed
>> 2.2) If it is owned by a PV guest with no device assigned,
> user space tools will try to replace the page with new one.
>> 2.3) It it is owned by a HVM guest with no device
> assigned, user space tools will try to live migration it.
>> 2.4) If it is owned by a guest with device assigned, user
> space tools can do live migration if needed.
>>
>> This patchset includes support for type 2.1/2.2.
>>
>> page_offfline_xen.patch gives basic support. The new
> hypercall (XEN_SYSCTL_page_offline) will mark a page offlining
> if the page is in-use, otherwise, it will remove the page from
> the page allocator. It also changes the free_heap_pages(), so
> that if a page_offlining page is freed, that page will be
> marked as page_offlined and will not be allocated anymore. One
> tricky thing is, the offlined page may not be buddy-aligned
> (i.e., it may be in the middle of a 2^order pages), so that we
> have to re-arrange the buddy system (i.e. &heap[][][]) carefully.
>>
>> page_offline_xen_memory.patch add support to PV guest, a new
> hypercall (XENMEM_page_offline) try to replace the old page
> with the new one. This will happen only when the guest has
> been suspeneded, to avoid complex page sharing situation. I'm
> still checking if more situation need be considered, like LDT
> pages and CR3 pages, so any suggestion is really great help.
>>
>> page_offline_tools.patch is an example user space tools
> based on libxc/xc_domain_save.c, it will try to firstly mark a
> page offline, and checking the result. If a page is owned by a
> PV guest, it will try to replace the pages.
>>
>> I did some basic testing, tried free pages and PV guest
> pages and is ok. Of course, I need more test on it. And more
> robust error handling is needed.
>>
>> Any suggestion is welcome.
>>
>> Thanks
>> Yunhong Jiang
>
>
>
>
>
> --
> Tim Deegan <Tim.Deegan@xxxxxxxxxx>
> Principal Software Engineer, Citrix Systems (R&D) Ltd.
> [Company #02300071, SL9 0DZ, UK.]
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