linux-kernel - Re: [RFC][Patch v8 0/7] KVM: Guest Free Page Hinting

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Message-ID: <8c65b48c-6e28-f28b-c8f0-5a2c78cf52a5@redhat.com>
Date:   Fri, 15 Feb 2019 07:40:55 -0500
From:   Nitesh Narayan Lal <nitesh@...hat.com>
To:     "Wang, Wei W" <wei.w.wang@...el.com>,
        'David Hildenbrand' <david@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "lcapitulino@...hat.com" <lcapitulino@...hat.com>,
        "pagupta@...hat.com" <pagupta@...hat.com>,
        "yang.zhang.wz@...il.com" <yang.zhang.wz@...il.com>,
        "riel@...riel.com" <riel@...riel.com>,
        "mst@...hat.com" <mst@...hat.com>,
        "dodgen@...gle.com" <dodgen@...gle.com>,
        "konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
        "dhildenb@...hat.com" <dhildenb@...hat.com>,
        "aarcange@...hat.com" <aarcange@...hat.com>
Subject: Re: [RFC][Patch v8 0/7] KVM: Guest Free Page Hinting


On 2/15/19 4:05 AM, Wang, Wei W wrote:
> On Thursday, February 14, 2019 5:43 PM, David Hildenbrand wrote:
>> Yes indeed, that is the important bit. They must not be put pack to the
>> buddy before they have been processed by the hypervisor. But as the pages
>> are not in the buddy, no one allocating a page will stumble over such a page
>> and try to allocate it. Threads trying to allocate memory will simply pick
>> another buddy page instead of "busy waiting" for that page to be finished
>> reporting.
> What if a guest thread try to allocate some pages but the buddy cannot satisfy
> because all the pages are isolated? Would it be the same case that the guest thread
> gets blocked by waiting all the isolated pages to get madvised by the host and
> returned to the guest buddy, or even worse, some guest threads get killed due to oom?

If you are referring to a situation when guest is under memory pressure
then isolation request will fail and memory will not be
reported/isolated. However, there can always be a corner case and we can
definitely take that into consideration later.

>
> Best,
> Wei
-- 
Regards
Nitesh



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