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

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Date:   Mon, 10 Feb 2020 03:13:21 +0000
From:   "Wang, Wei W" <wei.w.wang@...el.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        "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>,
        "david@...hat.com" <david@...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>
Subject: RE: [PATCH RFC] virtio_balloon: conservative balloon page shrinking

On Saturday, February 8, 2020 8:33 PM, Tetsuo Handa wrote:
> 
> Is this NUMA aware? Can "node-A's NR_FILE_PAGES is already 0 and
> node-B's NR_FILE_PAGES is not 0, but allocation request which triggered this
> shrinker wants to allocate from only node-B" happen? 

No, it's a global counter.

>Can some thread keep
> this shrinker defunctional by keep increasing NR_FILE_PAGES?

Yes. Actually it's our intention - as long as there are pagecache pages,
balloon pages are avoided to be reclaimed.


> 
> Is this patch from "Re: Balloon pressuring page cache" thread? I hope that
> the guest could start reclaiming memory based on host's request (like OOM
> notifier chain) which is issued when host thinks that host is getting close to
> OOM and thus guests should start returning their unused memory to host.
> Maybe "periodically (e.g. 5 minutes)" in addition to "upon close to OOM
> condition" is also possible.

That's about the host usages. The host side management software decides when to issue a request to balloon (either periodically or event driven), I think there isn't anything we need to do in the balloon driver here.

Best,
Wei