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

[Mel Gorman]

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@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxx/
> > > 
> > > 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