From: Alexander Duyck <alexander.h.duyck@linux.intel.com>
To: David Hildenbrand <david@redhat.com>,
Alexander Duyck <alexander.duyck@gmail.com>,
virtio-dev@lists.oasis-open.org, kvm@vger.kernel.org,
mst@redhat.com, dave.hansen@intel.com,
linux-kernel@vger.kernel.org, willy@infradead.org,
mhocko@kernel.org, linux-mm@kvack.org,
akpm@linux-foundation.org, mgorman@techsingularity.net,
vbabka@suse.cz, osalvador@suse.de
Cc: yang.zhang.wz@gmail.com, pagupta@redhat.com,
konrad.wilk@oracle.com, nitesh@redhat.com, riel@surriel.com,
lcapitulino@redhat.com, wei.w.wang@intel.com,
aarcange@redhat.com, pbonzini@redhat.com,
dan.j.williams@intel.com
Subject: Re: [PATCH v11 0/6] mm / virtio: Provide support for unused page reporting
Date: Tue, 01 Oct 2019 09:21:46 -0700 [thread overview]
Message-ID: <1ea1a4e11617291062db81f65745b9c95fd0bb30.camel@linux.intel.com> (raw)
In-Reply-To: <7233498c-2f64-d661-4981-707b59c78fd5@redhat.com>
On Tue, 2019-10-01 at 17:35 +0200, David Hildenbrand wrote:
> On 01.10.19 17:29, Alexander Duyck wrote:
> > This series provides an asynchronous means of reporting to a hypervisor
> > that a guest page is no longer in use and can have the data associated
> > with it dropped. To do this I have implemented functionality that allows
> > for what I am referring to as unused page reporting. The advantage of
> > unused page reporting is that we can support a significant amount of
> > memory over-commit with improved performance as we can avoid having to
> > write/read memory from swap as the VM will instead actively participate
> > in freeing unused memory so it doesn't have to be written.
> >
> > The functionality for this is fairly simple. When enabled it will allocate
> > statistics to track the number of reported pages in a given free area.
> > When the number of free pages exceeds this value plus a high water value,
> > currently 32, it will begin performing page reporting which consists of
> > pulling non-reported pages off of the free lists of a given zone and
> > placing them into a scatterlist. The scatterlist is then given to the page
> > reporting device and it will perform the required action to make the pages
> > "reported", in the case of virtio-balloon this results in the pages being
> > madvised as MADV_DONTNEED. After this they are placed back on their
> > original free list. If they are not merged in freeing an additional bit is
> > set indicating that they are a "reported" buddy page instead of a standard
> > buddy page. The cycle then repeats with additional non-reported pages
> > being pulled until the free areas all consist of reported pages.
> >
> > In order to try and keep the time needed to find a non-reported page to
> > a minimum we maintain a "reported_boundary" pointer. This pointer is used
> > by the get_unreported_pages iterator to determine at what point it should
> > resume searching for non-reported pages. In order to guarantee pages do
> > not get past the scan I have modified add_to_free_list_tail so that it
> > will not insert pages behind the reported_boundary. Doing this allows us
> > to keep the overhead to a minimum as re-walking the list without the
> > boundary will result in as much as 18% additional overhead on a 32G VM.
> >
> >
<snip>
> > As far as possible regressions I have focused on cases where performing
> > the hinting would be non-optimal, such as cases where the code isn't
> > needed as memory is not over-committed, or the functionality is not in
> > use. I have been using the will-it-scale/page_fault1 test running with 16
> > vcpus and have modified it to use Transparent Huge Pages. With this I see
> > almost no difference with the patches applied and the feature disabled.
> > Likewise I see almost no difference with the feature enabled, but the
> > madvise disabled in the hypervisor due to a device being assigned. With
> > the feature fully enabled in both guest and hypervisor I see a regression
> > between -1.86% and -8.84% versus the baseline. I found that most of the
> > overhead was due to the page faulting/zeroing that comes as a result of
> > the pages having been evicted from the guest.
>
> I think Michal asked for a performance comparison against Nitesh's
> approach, to evaluate if keeping the reported state + tracking inside
> the buddy is really worth it. Do you have any such numbers already? (or
> did my tired eyes miss them in this cover letter? :/)
>
I thought what Michal was asking for was what was the benefit of using the
boundary pointer. I added a bit up above and to the description for patch
3 as on a 32G VM it adds up to about a 18% difference without factoring in
the page faulting and zeroing logic that occurs when we actually do the
madvise.
Do we have a working patch set for Nitesh's code? The last time I tried
running his patch set I ran into issues with kernel panics. If we have a
known working/stable patch set I can give it a try.
- Alex
next prev parent reply other threads:[~2019-10-01 16:21 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-01 15:29 [PATCH v11 0/6] mm / virtio: Provide support for unused page reporting Alexander Duyck
2019-10-01 15:29 ` [PATCH v11 1/6] mm: Adjust shuffle code to allow for future coalescing Alexander Duyck
2019-10-01 15:29 ` [PATCH v11 2/6] mm: Use zone and order instead of free area in free_list manipulators Alexander Duyck
2019-10-15 0:42 ` [mm] 2eca680594: will-it-scale.per_process_ops -2.5% regression kernel test robot
2019-10-01 15:29 ` [PATCH v11 3/6] mm: Introduce Reported pages Alexander Duyck
2019-10-01 15:29 ` [PATCH v11 4/6] mm: Add device side and notifier for unused page reporting Alexander Duyck
2019-10-01 15:29 ` [PATCH v11 5/6] virtio-balloon: Pull page poisoning config out of free page hinting Alexander Duyck
2019-10-01 15:29 ` [PATCH v11 6/6] virtio-balloon: Add support for providing unused page reports to host Alexander Duyck
2019-10-01 15:31 ` [PATCH v11 QEMU 1/3] virtio-ballon: Implement support for page poison tracking feature Alexander Duyck
2019-10-01 15:31 ` [PATCH v11 QEMU 2/3] virtio-balloon: Add bit to notify guest of unused page reporting Alexander Duyck
2019-10-01 15:31 ` [PATCH v11 QEMU 3/3] virtio-balloon: Provide a interface for " Alexander Duyck
2019-10-01 15:35 ` [PATCH v11 0/6] mm / virtio: Provide support " David Hildenbrand
2019-10-01 16:21 ` Alexander Duyck [this message]
2019-10-01 18:41 ` David Hildenbrand
2019-10-01 19:17 ` Nitesh Narayan Lal
2019-10-01 19:08 ` Michael S. Tsirkin
2019-10-01 19:16 ` Nitesh Narayan Lal
2019-10-01 20:25 ` Alexander Duyck
2019-10-01 20:49 ` Alexander Duyck
2019-10-01 20:51 ` Dave Hansen
2019-10-02 15:04 ` Nitesh Narayan Lal
2019-10-02 14:41 ` [virtio-dev] " Nitesh Narayan Lal
2019-10-02 0:55 ` Alexander Duyck
2019-10-02 7:13 ` David Hildenbrand
2019-10-02 10:44 ` Nitesh Narayan Lal
2019-10-02 10:36 ` Nitesh Narayan Lal
2019-10-02 14:25 ` Alexander Duyck
2019-10-02 14:36 ` Nitesh Narayan Lal
2019-10-07 12:29 ` Nitesh Narayan Lal
2019-10-07 15:33 ` Alexander Duyck
2019-10-07 16:19 ` Nitesh Narayan Lal
2019-10-07 16:27 ` Alexander Duyck
2019-10-07 17:06 ` Nitesh Narayan Lal
2019-10-07 17:20 ` Alexander Duyck
2019-10-09 16:25 ` Nitesh Narayan Lal
2019-10-09 16:25 ` Nitesh Narayan Lal
2019-10-09 16:50 ` Alexander Duyck
2019-10-09 17:08 ` Nitesh Narayan Lal
2019-10-09 17:26 ` Alexander Duyck
2019-10-09 15:21 ` Nitesh Narayan Lal
2019-10-09 16:35 ` Alexander Duyck
2019-10-09 16:35 ` Alexander Duyck
2019-10-09 19:46 ` Nitesh Narayan Lal
2019-10-10 7:36 ` David Hildenbrand
2019-10-10 10:27 ` Nitesh Narayan Lal
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