linux-kernel - use of shrinker in virtio balloon free page hinting

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Date:   Wed, 17 Jul 2019 07:20:33 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     wei.w.wang@...el.com, Nitesh Narayan Lal <nitesh@...hat.com>,
        kvm list <kvm@...r.kernel.org>,
        David Hildenbrand <david@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Yang Zhang <yang.zhang.wz@...il.com>, pagupta@...hat.com,
        Rik van Riel <riel@...riel.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        lcapitulino@...hat.com, Andrea Arcangeli <aarcange@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>, dan.j.williams@...el.com,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>
Subject: use of shrinker in virtio balloon free page hinting

Wei, others,

ATM virtio_balloon_shrinker_scan will only get registered
when deflate on oom feature bit is set.

Not sure whether that's intentional.  Assuming it is:

virtio_balloon_shrinker_scan will try to locate and free
pages that are processed by host.
The above seems broken in several ways:
- count ignores the free page list completely
- if free pages are being reported, pages freed
  by shrinker will just get re-allocated again

I was unable to make this part of code behave in any reasonable
way - was shrinker usage tested? What's a good way to test that?

Thanks!

-- 
MST