linux-kernel - Re: [PATCH v1 6/6] virtio-balloon: Add support for aerating memory via hinting

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Message-ID: <20190718162502-mutt-send-email-mst@kernel.org>
Date:   Thu, 18 Jul 2019 16:27:55 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Nitesh Narayan Lal <nitesh@...hat.com>
Cc:     Alexander Duyck <alexander.duyck@...il.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, wei.w.wang@...el.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: Re: [PATCH v1 6/6] virtio-balloon: Add support for aerating memory
 via hinting

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