linux-kernel - Re: [PATCH v12 0/6] mm / virtio: Provide support for unused page reporting

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Message-ID: <7c3af266-113c-c695-d78a-1f400a871448@redhat.com>
Date:   Wed, 23 Oct 2019 07:19:06 -0400
From:   Nitesh Narayan Lal <nitesh@...hat.com>
To:     Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Duyck <alexander.duyck@...il.com>, david@...hat.com
Cc:     kvm@...r.kernel.org, mst@...hat.com, linux-kernel@...r.kernel.org,
        willy@...radead.org, mhocko@...nel.org, linux-mm@...ck.org,
        mgorman@...hsingularity.net, vbabka@...e.cz,
        yang.zhang.wz@...il.com, konrad.wilk@...cle.com,
        pagupta@...hat.com, riel@...riel.com, lcapitulino@...hat.com,
        dave.hansen@...el.com, wei.w.wang@...el.com, aarcange@...hat.com,
        pbonzini@...hat.com, dan.j.williams@...el.com, osalvador@...e.de
Subject: Re: [PATCH v12 0/6] mm / virtio: Provide support for unused page
 reporting


On 10/22/19 7:43 PM, Alexander Duyck wrote:
> On Tue, 2019-10-22 at 16:01 -0700, Andrew Morton wrote:
>> On Tue, 22 Oct 2019 15:27:52 -0700 Alexander Duyck <alexander.duyck@...il.com> wrote:
>>
[...]
>>> There is currently an alternative patch set[1] that has been under work
>>> for some time however the v12 version of that patch set could not be
>>> tested as it triggered a kernel panic when I attempted to test it. It
>>> requires multiple modifications to get up and running with performance
>>> comparable to this patch set. A follow-on set has yet to be posted. As
>>> such I have not included results from that patch set, and I would
>>> appreciate it if we could keep this patch set the focus of any discussion
>>> on this thread.
>> Actually, the rest of us would be interested in a comparison ;)  
> I understand that. However, the last time I tried benchmarking that patch
> set it blew up into a thread where we kept having to fix things on that
> patch set and by the time we were done we weren't benchmarking the v12
> patch set anymore since we had made so many modifications to it, and that 
> assumes Nitesh and I were in sync. Also I don't know what the current
> state of his patch set is as he was working on some additional changes
> when we last discussed things.

Just an update about the current state of my patch-series:

As we last discussed I was going to try implementing Michal Hock's suggestion of
using page-isolation APIs. To do that I have replaced __isolate_free_page() with
start/undo_isolate_free_page_range().
However, I am running into some issues which I am currently investigating.

After this, I will be investigating the reason why I was seeing degradation
specifically with (MAX_ORDER - 2) as the reporting order.

>
> Ideally that patch set can be reposted with the necessary fixes and then
> we can go through any necessary debug, repair, and addressing limitations
> there.
>
>