linux-kernel - Re: [PATCH v2 2/2] virtio_balloon: replace oom notifier with shrinker

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Message-ID: <87d7ae45-79cb-e294-7397-0e45e2af49cd@I-love.SAKURA.ne.jp>
Date:   Thu, 2 Aug 2018 20:00:32 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Wei Wang <wei.w.wang@...el.com>, Michal Hocko <mhocko@...nel.org>
Cc:     virtio-dev@...ts.oasis-open.org, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, linux-mm@...ck.org,
        mst@...hat.com, akpm@...ux-foundation.org
Subject: Re: [PATCH v2 2/2] virtio_balloon: replace oom notifier with shrinker

On 2018/08/02 19:32, Wei Wang wrote:
> On 08/01/2018 07:34 PM, Michal Hocko wrote:
>> Do you have any numbers for how does this work in practice?
> 
> It works in this way: for example, we can set the parameter, balloon_pages_to_shrink,
> to shrink 1GB memory once shrink scan is called. Now, we have a 8GB guest, and we balloon
> out 7GB. When shrink scan is called, the balloon driver will get back 1GB memory and give
> them back to mm, then the ballooned memory becomes 6GB.

Since shrinker might be called concurrently (am I correct?), the balloon might deflate
far more than needed if it releases such much memory. If shrinker is used, releasing 256
pages might be sufficient.