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From:   "Wang, Wei W" <wei.w.wang@intel.com>
To:     David Hildenbrand <david@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "virtualization@lists.linux-foundation.org" 
        <virtualization@lists.linux-foundation.org>,
        Tyler Sanderson <tysand@google.com>,
        "Michael S . Tsirkin" <mst@redhat.com>,
        Alexander Duyck <alexander.h.duyck@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Nadav Amit <namit@vmware.com>, Michal Hocko <mhocko@kernel.org>
Subject: RE: [PATCH v1 3/3] virtio-balloon: Switch back to OOM handler for
 VIRTIO_BALLOON_F_DEFLATE_ON_OOM
Thread-Topic: [PATCH v1 3/3] virtio-balloon: Switch back to OOM handler for
 VIRTIO_BALLOON_F_DEFLATE_ON_OOM
Thread-Index: AQHV3EIpfQc0Q8o+LUGdBo475Vlup6gN3WAA
Date:   Thu, 6 Feb 2020 08:57:05 +0000
Message-ID: <286AC319A985734F985F78AFA26841F73E4237B0@shsmsx102.ccr.corp.intel.com>
References: <20200205163402.42627-1-david@redhat.com>
 <20200205163402.42627-4-david@redhat.com>
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On Thursday, February 6, 2020 12:34 AM, David Hildenbrand wrote:
> Commit 71994620bb25 ("virtio_balloon: replace oom notifier with shrinker")
> changed the behavior when deflation happens automatically. Instead of
> deflating when called by the OOM handler, the shrinker is used.
> 
> However, the balloon is not simply some slab cache that should be shrunk
> when under memory pressure. The shrinker does not have a concept of
> priorities, so this behavior cannot be configured.
> 
> There was a report that this results in undesired side effects when inflating
> the balloon to shrink the page cache. [1]
> 	"When inflating the balloon against page cache (i.e. no free memory
> 	 remains) vmscan.c will both shrink page cache, but also invoke the
> 	 shrinkers -- including the balloon's shrinker. So the balloon
> 	 driver allocates memory which requires reclaim, vmscan gets this
> 	 memory by shrinking the balloon, and then the driver adds the
> 	 memory back to the balloon. Basically a busy no-op."

Not sure if we need to go back to OOM, which has many drawbacks as we discussed.
Just posted out another approach, which is simple.

Best,
Wei