Re: [Minios-devel] [UNIKRAFT PATCH 17/22] plat/kvm: arm64: Calculate pagetable size dynamically by image size

["Wei Chen (Arm Technology China)" <Wei.Chen@xxxxxxx>]

Hi Julien,

> -----Original Message-----
> From: Julien Grall <julien.grall@xxxxxxx>
> Sent: 2018年11月9日 18:20
> To: Wei Chen (Arm Technology China) <Wei.Chen@xxxxxxx>; minios-
> devel@xxxxxxxxxxxxxxxxxxxx; simon.kuenzer@xxxxxxxxx
> Cc: Kaly Xin (Arm Technology China) <Kaly.Xin@xxxxxxx>; nd <nd@xxxxxxx>
> Subject: Re: [Minios-devel] [UNIKRAFT PATCH 17/22] plat/kvm: arm64: Calculate
> pagetable size dynamically by image size
> 
> 
> 
> On 09/11/2018 07:48, Wei Chen (Arm Technology China) wrote:
> > Hi Julien,
> 
> Hi Wei,
> 
> >
> >> -----Original Message-----
> >> From: Julien Grall <julien.grall@xxxxxxx>
> >> Sent: 2018年11月8日 20:25
> >> To: Wei Chen (Arm Technology China) <Wei.Chen@xxxxxxx>; minios-
> >> devel@xxxxxxxxxxxxxxxxxxxx; simon.kuenzer@xxxxxxxxx
> >> Cc: Kaly Xin (Arm Technology China) <Kaly.Xin@xxxxxxx>; nd <nd@xxxxxxx>
> >> Subject: Re: [Minios-devel] [UNIKRAFT PATCH 17/22] plat/kvm: arm64:
> Calculate
> >> pagetable size dynamically by image size
> >>
> >>
> >>
> >> On 11/8/18 9:51 AM, Wei Chen wrote:
> >>> The previous L3 page table size is a fixed value based on the
> >>> assumption that, image size will not exceed 2MB. But that's not
> >>> true, some applications like node.js will be about 40MB after
> >>> converting to Unikernel. So in this patch, we calculate the
> >>> page table size by real image size. In order to mapping the
> >>> image occupied memory to L3 page table, we round up the image
> >>> size with 2MB.
> >>
> >> I am a bit confused, you speak about L3 page-table, but as you round up
> >> to 2MB, why don't you map using 2MB superpage?
> >
> > Because the section is 4KB alignment, and we will assign different
> > attributes for different sections.
> 
> Sorry I misread the code.
> 
> > We roundup image size to 2MB to
> > avoid making holes in L3 table
> 
> What do you mean? What's wrong with making holes in L3 table?
> 

That would make some memory (that is not occupied by image but shared the same
2MB block with image tail) unmapped.


> Cheers,
> 
> --
> Julien Grall
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