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





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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