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

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Message-ID: <20200219084912.GO3466@techsingularity.net>
Date:   Wed, 19 Feb 2020 08:49:12 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Alexander Duyck <alexander.h.duyck@...ux.intel.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        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,
        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, Feb 18, 2020 at 08:37:46AM -0800, Alexander Duyck wrote:
> On Tue, 2020-02-11 at 16:19 -0800, Andrew Morton wrote:
> > 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.
> > 
> 
> Mel,
> 
> Any ETA on when you would be available to review these patches? They are
> now in Andrew's tree and in linux-next. I am hoping to get any remaining
> review from the community sorted out in the next few weeks so I can move
> onto focusing on how best to exert pressure on the page cache so that we
> can keep the guest memory footprint small.
> 

I hope to get to it soon. I'm trying to finalise a scheduler-related
series that reconciles NUMA and CPU balancing and it's occupying much of
my attention available for mainline development :(

-- 
Mel Gorman
SUSE Labs