linux-kernel - Re: [PATCH v13 4/5] mm: support reporting free page blocks

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Date:   Fri, 04 Aug 2017 16:55:22 +0800
From:   Wei Wang <wei.w.wang@...el.com>
To:     Michal Hocko <mhocko@...nel.org>
CC:     "Michael S. Tsirkin" <mst@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "mawilcox@...rosoft.com" <mawilcox@...rosoft.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "virtio-dev@...ts.oasis-open.org" <virtio-dev@...ts.oasis-open.org>,
        "david@...hat.com" <david@...hat.com>,
        "cornelia.huck@...ibm.com" <cornelia.huck@...ibm.com>,
        "mgorman@...hsingularity.net" <mgorman@...hsingularity.net>,
        "aarcange@...hat.com" <aarcange@...hat.com>,
        "amit.shah@...hat.com" <amit.shah@...hat.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "liliang.opensource@...il.com" <liliang.opensource@...il.com>,
        "yang.zhang.wz@...il.com" <yang.zhang.wz@...il.com>,
        "quan.xu@...yun.com" <quan.xu@...yun.com>
Subject: Re: [PATCH v13 4/5] mm: support reporting free page blocks

On 08/04/2017 04:24 PM, Michal Hocko wrote:
>
>> For our use case, the callback just puts the reported page
>> block to the ring, then returns. If the ring is full as the host
>> is busy, then I think it should skip this one, and just return.
>> Because:
>>      A. This is an optimization feature, losing a couple of free
>>           pages to report isn't that important;
>>      B. In reality, I think it's uncommon to see this ring getting
>>          full (I didn't observe ring full in the tests), since the host
>>          (consumer) is notified to take out the page block right
>>          after it is added.
> I thought you only updated a pre allocated bitmat... Anyway, I cannot
> comment on this part much as I am not familiar with your usecase.
>   

Actually the bitmap is in the hypervisor (host). The callback puts the
(pfn,size) on a ring which is shared with the hypervisor, then the
hypervisor takes that info from the ring and updates that bitmap.


Best,
Wei