RE: Re: [PATCH] Support swap a page from user space tools -- Was RE: [RFC][PATCH] Basic support for page offline

["Jiang, Yunhong" <yunhong.jiang@intel.com>]

Keir Fraser <mailto:keir.fraser@eu.citrix.com> wrote:
> On 20/03/2009 09:16, "Jiang, Yunhong" <yunhong.jiang@intel.com> wrote:
> 
>>> Thanks for the description. I guess I will wait for your next patch, which
>>> should I think at least separate the foreign pagetable update hypercall
>>> from 
>> 
>> I think I have split that patch last night. There is no foreign page table
>> hypercall anymore, instead, I just tried to enhance the current mmu_op. And
>> this new "weird" swap is now named mmu_ext_exchange_page.(Is it really so
>> weird to just pass the new mfn down?)
> 
> Ah yes, I found the email now. Well I'm still confused as to why it is
> needed. It seems to me you could scan for all PTEs mapping
> old_pfn, stash
> them in a list and temporarily make them not-present, and take
> a copy of
> old_pfn. Then do a normal XENMEM_exchange: on failure revert
> all PTEs, on
> success switch over all PTEs and copy old_pfn data into
> new_pfn. Well it is
> more hypercalls (two updates per PTE) I suppose, but I doubt
> this matters
> unless you're offlining a lot of pages, and we don't support offlining
> memory banks really at the moment. Also some of this will
> potentially batch
> up into multicalls or MMUOP_ lists nicely anyway.

Yes, seems this method works well. The only change to Xen is to enhance current mmu_xxx_pt_update to support foreign page table.

I will update the patch accordingly to see if it can pass the review  :-)

Thanks
Yunhong Jiang

> 
> -- Keir