linux-kernel - Re: [PATCH v17 0/9] mm / virtio: Provide support for free page reporting

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Date:   Tue, 11 Feb 2020 16:19:27 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Alexander Duyck <alexander.h.duyck@...ux.intel.com>
Cc:     Alexander Duyck <alexander.duyck@...il.com>, kvm@...r.kernel.org,
        david@...hat.com, mst@...hat.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, mgorman@...hsingularity.net,
        yang.zhang.wz@...il.com, pagupta@...hat.com,
        konrad.wilk@...cle.com, nitesh@...hat.com, riel@...riel.com,
        willy@...radead.org, lcapitulino@...hat.com, dave.hansen@...el.com,
        wei.w.wang@...el.com, aarcange@...hat.com, pbonzini@...hat.com,
        dan.j.williams@...el.com, mhocko@...nel.org, vbabka@...e.cz,
        osalvador@...e.de
Subject: Re: [PATCH v17 0/9] mm / virtio: Provide support for free page
 reporting

On Tue, 11 Feb 2020 15:55:31 -0800 Alexander Duyck <alexander.h.duyck@...ux.intel.com> wrote:

> On the host I just have to monitor /proc/meminfo and I can see the
> difference. I get the following results on the host, in the enabled case
> it takes about 30 seconds for it to settle into the final state since I
> only report page a bit at a time:
> Baseline/Applied
>   MemTotal:    131963012 kB
>   MemFree:      95189740 kB
> 
> Enabled:
>   MemTotal:    131963012 kB
>   MemFree:     126459472 kB
> 
> This is what I was referring to with the comment above. I had a test I was
> running back around the first RFC that consisted of bringing up enough VMs
> so that there was a bit of memory overcommit and then having the VMs in
> turn run memhog. As I recall the difference between the two was  something
> like a couple minutes to run through all the VMs as the memhog would take
> up to 40+ seconds for one that was having to pull from swap while it took
> only 5 to 7 seconds for the VMs that were all running the page hinting.
> 
> I had referenced it here in the RFC:
> https://lore.kernel.org/lkml/20190204181118.12095.38300.stgit@localhost.localdomain/
> 
> I have been verifying the memory has been getting freed but didn't feel
> like the test added much value so I haven't added it to the cover page for
> a while since the time could vary widely and is dependent on things like
> the disk type used for the host swap since my SSD is likely faster than
> spinning rust, but may not be as fast as other SSDs on the market. Since
> the disk speed can play such a huge role I wasn't comfortable posting
> numbers since the benefits could vary so widely.

OK, thanks.  I'll add the patches to the mm pile.  The new
mm/page_reporting.c is unreviewed afaict, so I guess you own that for
now ;)

It would be very nice to get some feedback from testers asserting "yes,
this really helped my workload" but I understand this sort of testing
is hard to obtain at this stage.