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Date:   Thu, 18 Jul 2019 16:27:55 -0400
From:   "Michael S. Tsirkin" <mst@redhat.com>
To:     Nitesh Narayan Lal <nitesh@redhat.com>
Cc:     Alexander Duyck <alexander.duyck@gmail.com>,
        kvm list <kvm@vger.kernel.org>,
        David Hildenbrand <david@redhat.com>,
        Dave Hansen <dave.hansen@intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Yang Zhang <yang.zhang.wz@gmail.com>, pagupta@redhat.com,
        Rik van Riel <riel@surriel.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        lcapitulino@redhat.com, wei.w.wang@intel.com,
        Andrea Arcangeli <aarcange@redhat.com>,
        Paolo Bonzini <pbonzini@redhat.com>, dan.j.williams@intel.com,
        Alexander Duyck <alexander.h.duyck@linux.intel.com>
Subject: Re: [PATCH v1 6/6] virtio-balloon: Add support for aerating memory
 via hinting
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On Thu, Jul 18, 2019 at 12:03:23PM -0400, Nitesh Narayan Lal wrote:
> >>>> For example we allocate pages until shrinker kicks in.
> >>>> Fair enough but in fact many it would be better to
> >>>> do the reverse: trigger shrinker and then send as many
> >>>> free pages as we can to host.
> >>> I'm not sure I understand this last part.
> >> Oh basically what I am saying is this: one of the reasons to use page
> >> hinting is when host is short on memory.  In that case, why don't we use
> >> shrinker to ask kernel drivers to free up memory? Any memory freed could
> >> then be reported to host.
> > Didn't the balloon driver already have a feature like that where it
> > could start shrinking memory if the host was under memory pressure?
> If you are referring to auto-ballooning (I don't think it is merged). It
> has its own set of disadvantages such as it could easily lead to OOM,
> memory corruption and so on.

Right. So what I am saying is: we could have a flag that triggers a
shrinker once before sending memory hints.
Worth considering.

-- 
MST