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Subject: Re: [PATCH RFC] virtio_balloon: conservative balloon page shrinking
To:     "Wang, Wei W" <wei.w.wang@intel.com>
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From:   Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
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Date:   Tue, 11 Feb 2020 23:18:56 +0900
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On 2020/02/10 16:27, Wang, Wei W wrote:
>> Well, my comment is rather: "Do not try to reserve guest's memory. In other
>> words, do not try to maintain balloons on the guest side. Since host would
>> be able to cache file data on the host's cache, guests would be able to
>> quickly fetch file data from host's cache via normal I/O requests." ;-)
> 
> Didn't this one. The discussion was about guest pagecache pages v.s. guest balloon pages.
> Why is host's pagecache here?

I'm expecting a mode: "Guests should try to minimize pagecache pages (and teach
host to treat reclaimed pages as if POSIX_FADV_DONTNEED) instead of managing
guest balloon pages". In other words, as if

  while :; sleep 5; echo 1 > /proc/sys/vm/drop_caches; done

is running in the guest's kernel. And as if

  echo 2 > /proc/sys/vm/drop_caches

is triggered in the guest's kernel when host requested guests to reclaim
memory. No long-life balloons. Guest balloons do not need to care about
NUMA. Just leave the management of pagecache pages to the host.