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Re: [PATCH v3 14/22] microvm: use 2G split unconditionally
From: |
Paolo Bonzini |
Subject: |
Re: [PATCH v3 14/22] microvm: use 2G split unconditionally |
Date: |
Wed, 27 May 2020 16:54:34 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 |
On 27/05/20 16:26, Igor Mammedov wrote:
> On Wed, 27 May 2020 15:06:28 +0200
> Paolo Bonzini <address@hidden> wrote:
>
>> On 27/05/20 14:25, Igor Mammedov wrote:
>>>> (2) we loose a gigabyte page.
>>> I'm not sure waht exactly we loose in this case.
>>> Lets assume we allocating guest 5G of continuous RAM using 1G
>>> huge pages,
>>> in this case I'd think that on host side MMIO overlay won't
>>> affect RAM blob
>>> on guest side pagetables will be fragmented due to MMIO holes,
>>> but guest still
>>> could use huge pages smaller ones in fragmented area and 1G where
>>> there is no fragmentation.
>>
>> Access to the 3G-4G area would not be able to use 1G EPT pages.
> Could it use 2Mb pages instead of 1Gb?
Yes, probably a mix of 2 MiB pages and 4 KiB pages around the memslot
splits.
> Do we really care about 1 gigabyte huge page in microvm intended usecase?
> (fast starting VMs for microservices like FaaS, which unlikely would use much
> memory to begin with)
I honestly don't think it's measurable, but at least in theory we care
because such workloads could have more TLB misses (relative to the
execution time) than long-lasting VMs.
Paolo
- Re: [PATCH v3 14/22] microvm: use 2G split unconditionally, (continued)
- Re: [PATCH v3 14/22] microvm: use 2G split unconditionally, Philippe Mathieu-Daudé, 2020/05/20
- Re: [PATCH v3 14/22] microvm: use 2G split unconditionally, Igor Mammedov, 2020/05/21
- Re: [PATCH v3 14/22] microvm: use 2G split unconditionally, Igor Mammedov, 2020/05/21
- Re: [PATCH v3 14/22] microvm: use 2G split unconditionally, Gerd Hoffmann, 2020/05/25
- Re: [PATCH v3 14/22] microvm: use 2G split unconditionally, Igor Mammedov, 2020/05/25
- Re: [PATCH v3 14/22] microvm: use 2G split unconditionally, Gerd Hoffmann, 2020/05/26
- Re: [PATCH v3 14/22] microvm: use 2G split unconditionally, Igor Mammedov, 2020/05/27
- Re: [PATCH v3 14/22] microvm: use 2G split unconditionally, Paolo Bonzini, 2020/05/27
- Re: [PATCH v3 14/22] microvm: use 2G split unconditionally, Igor Mammedov, 2020/05/27
- Re: [PATCH v3 14/22] microvm: use 2G split unconditionally, Igor Mammedov, 2020/05/27
- Re: [PATCH v3 14/22] microvm: use 2G split unconditionally,
Paolo Bonzini <=
- Re: [PATCH v3 14/22] microvm: use 2G split unconditionally, Gerd Hoffmann, 2020/05/28
- Re: [PATCH v3 14/22] microvm: use 2G split unconditionally, Gerd Hoffmann, 2020/05/28
[PATCH v3 21/22] [RfC] acpi: add per machine type acpi default, Gerd Hoffmann, 2020/05/20
[PATCH v3 20/22] microvm/acpi: disable virtio-mmio cmdline hack, Gerd Hoffmann, 2020/05/20
[PATCH v3 22/22] [RfC] acpi: flip default to off for microvm, Gerd Hoffmann, 2020/05/20
[PATCH v3 09/22] acpi: ged: rename event memory region, Gerd Hoffmann, 2020/05/20