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Date:   Thu, 12 Jul 2018 19:34:16 +0800
From:   Wei Wang <wei.w.wang@...el.com>
To:     Michal Hocko <mhocko@...nel.org>
CC:     Linus Torvalds <torvalds@...ux-foundation.org>,
        virtio-dev@...ts.oasis-open.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        KVM list <kvm@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        liliang.opensource@...il.com, yang.zhang.wz@...il.com,
        quan.xu0@...il.com, nilal@...hat.com,
        Rik van Riel <riel@...hat.com>, peterx@...hat.com
Subject: Re: [PATCH v35 1/5] mm: support to get hints of free page blocks

On 07/12/2018 04:13 PM, Michal Hocko wrote:
> On Thu 12-07-18 10:52:08, Wei Wang wrote:
>> On 07/12/2018 10:30 AM, Linus Torvalds wrote:
>>> On Wed, Jul 11, 2018 at 7:17 PM Wei Wang <wei.w.wang@...el.com> wrote:
>>>> Would it be better to remove __GFP_THISNODE? We actually want to get all
>>>> the guest free pages (from all the nodes).
>>> Maybe. Or maybe it would be better to have the memory balloon logic be
>>> per-node? Maybe you don't want to remove too much memory from one
>>> node? I think it's one of those "play with it" things.
>>>
>>> I don't think that's the big issue, actually. I think the real issue
>>> is how to react quickly and gracefully to "oops, I'm trying to give
>>> memory away, but now the guest wants it back" while you're in the
>>> middle of trying to create that 2TB list of pages.
>> OK. virtio-balloon has already registered an oom notifier
>> (virtballoon_oom_notify). I plan to add some control there. If oom happens,
>> - stop the page allocation;
>> - immediately give back the allocated pages to mm.
> Please don't. Oom notifier is an absolutely hideous interface which
> should go away sooner or later (I would much rather like the former) so
> do not build a new logic on top of it. I would appreciate if you
> actually remove the notifier much more.
>
> You can give memory back from the standard shrinker interface. If we are
> reaching low reclaim priorities then we are struggling to reclaim memory
> and then you can start returning pages back.

OK. Just curious why oom notifier is thought to be hideous, and has it 
been a consensus?

Best,
Wei

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