linux-kernel - Re: [PATCH RFC] virtio_balloon: conservative balloon page shrinking

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Message-ID: <80f975c9-5f18-a613-6412-292dafd34dfe@redhat.com>
Date:   Thu, 6 Feb 2020 10:32:20 +0100
From:   David Hildenbrand <david@...hat.com>
To:     "Wang, Wei W" <wei.w.wang@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>
Cc:     "tysand@...gle.com" <tysand@...gle.com>,
        "mst@...hat.com" <mst@...hat.com>,
        "alexander.h.duyck@...ux.intel.com" 
        <alexander.h.duyck@...ux.intel.com>,
        "rientjes@...gle.com" <rientjes@...gle.com>,
        "mhocko@...nel.org" <mhocko@...nel.org>,
        "namit@...are.com" <namit@...are.com>,
        "penguin-kernel@...ove.SAKURA.ne.jp" 
        <penguin-kernel@...ove.SAKURA.ne.jp>
Subject: Re: [PATCH RFC] virtio_balloon: conservative balloon page shrinking

On 06.02.20 10:28, Wang, Wei W wrote:
> On Thursday, February 6, 2020 5:10 PM, David Hildenbrand wrote:
>> so dropping caches (echo 3 > /proc/sys/vm/drop_caches) will no longer
>> deflate the balloon when conservative_shrinker=true?
>>
> 
> Should be. Need Tyler's help to test it.
> 

If the page cache is empty, a drop_slab() will deflate the whole balloon
if I am not wrong.

Especially, a echo 3 > /proc/sys/vm/drop_caches

will first drop the page cache and then drop_slab()

While I like the general idea, it looks more like a hack to me, to try
to teach the shrinker something it was not built for/does not support yet.

-- 
Thanks,

David / dhildenb