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

[Julien Grall <julien.grall@xxxxxxx>]

On 11/15/18 2:43 AM, Wei Chen (Arm Technology China) wrote:
> Hi Julien,
Hi Wei,

> > -----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.
Fair enough. Please mention it in the commit message and likely in the code.

Cheers,

--
Julien Grall

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