Re: PATCH: Hugepage support for Domains booting with 4KB pages

[Keir Fraser <keir.xen@gmail.com>]

On 22/03/2011 12:36, "Keshav Darak" <keshav_darak@yahoo.com> wrote:

> Keir,
>     We are aware of it and we have to use 'opt_allow_superpages' boolean flag
> in our implementation too. But when we use superpages flag in domain
> configuration file,
> entire domain boots on hugepages (superpages).If the specified memory in
> 'hugepages' for the domain is not available, then the domain does not boot.
>      But in our implementation , we target to give only those many hugepages (
> using "hugepage_num" option in config file) to the domain that it actually
> requires and hence entire domain need not be booted on hugepages.
>      This is to support domains that boot with 4 KB pages and still can use
> hugepages. So,
> the pressure on the number of hugepages required for a domain even to boot is
> reduced to a great extent.

Okay, I don't see why that would need further changes in the hypervisor
itself, however.

 -- Keir

> --- On Mon, 3/21/11, Keir Fraser <keir.xen@gmail.com> wrote:
>> 
>> From: Keir Fraser <keir.xen@gmail.com>
>> Subject: Re: [Xen-devel] PATCH: Hugepage support for Domains booting with 4KB
>> pages
>> To: "Keshav Darak" <keshav_darak@yahoo.com>, xen-devel@lists.xensource.com
>> Cc: jeremy@goop.org
>> Date: Monday, March 21, 2011, 9:31 PM
>> 
>> Keshav,
>> 
>> There is already optional support for superpage allocations and mappings for
>> PV guests in the hypervisor and toolstack. See the opt_allow_superpages
>> boolean flag in the hypervisor, and the 'superpages' domain config option
>> that can be specified when creating a new domain via xend/xm.
>> 
>>  -- Keir
>> 
>> On 21/03/2011 21:01, "Keshav Darak" <keshav_darak@yahoo.com
>> </mc/compose?to=keshav_darak@yahoo.com> > wrote:
>> 
>>> have corrected few mistakes in previously attached xen patch file.
>>> Please review it.
>>> 
>>> --- On Sun, 3/20/11, Keshav Darak <keshav_darak@yahoo.com
>>> </mc/compose?to=keshav_darak@yahoo.com> > wrote:
>>>> 
>>>> From: Keshav Darak <keshav_darak@yahoo.com
>>>> </mc/compose?to=keshav_darak@yahoo.com> >
>>>> Subject: [Xen-devel] PATCH: Hugepage support for Domains booting with 4KB
>>>> pages
>>>> To: xen-devel@lists.xensource.com
>>>> </mc/compose?to=xen-devel@lists.xensource.com>
>>>> Cc: jeremy@goop.org </mc/compose?to=jeremy@goop.org> , keir@xen.org
>>>> </mc/compose?to=keir@xen.org>
>>>> Date: Sunday, March 20, 2011, 10:34 PM
>>>> 
>>>> We have implemented hugepage support for guests in following manner
>>>> 
>>>> In our implementation we added a parameter hugepage_num which is specified
>>>> in
>>>> the config file of the DomU. It is the number of hugepages that the guest
>>>> is
>>>> guaranteed to receive whenever the kernel asks for hugepage by using its
>>>> boot
>>>> time parameter or reserving after booting (eg. Using echo XX >
>>>> /proc/sys/vm/nr_hugepages). During creation of the domain we reserve MFN's
>>>> for these hugepages and store them in the list. The listhead of this list
>>>> is
>>>> inside the domain structure with name "hugepage_list". When the domain is
>>>> booting, at that time the memory seen by the kernel is allocated memory
>>>> less
>>>> the amount required for hugepages. The function reserve_hugepage_range is
>>>> called as a initcall. Before this function the xen_extra_mem_start points
>>>> to
>>>> this apparent end of the memory. In this function we reserve the PFN range
>>>> for the hugepages which are going to be allocated by kernel by incrementing
>>>> the xen_extra_mem_start. We maintain these PFNs as pages in
>>>> "xen_hugepfn_list" in the kernel.
>>>> 
>>>> Now before the kernel requests for hugepages, it makes a hypercall
>>>> HYPERVISOR_memory_op  to get count of hugepages allocated to it and
>>>> accordingly reserves the pfn range.
>>>> then whenever kernel requests for hugepages it again make hypercall
>>>> HYPERVISOR_memory_op to get the preallocated hugepage and according makes
>>>> the
>>>> p2m mapping on both sides (xen as well as kernel side)
>>>> 
>>>> The approach can be better explained using the presentation attached.
>>>> 
>>>> --
>>>> Keshav Darak
>>>> Kaustubh Kabra
>>>> Ashwin Vasani 
>>>> Aditya Gadre
>>>> 
>>>>  
>>>> 
>>>> -----Inline Attachment Follows-----
>>>> 
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>>> 
>>> 
>> 
>> 
> 
>