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From: Alexander Duyck <alexander.duyck@gmail.com>
To: David Hildenbrand <david@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>,
	virtio-dev@lists.oasis-open.org, kvm list <kvm@vger.kernel.org>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Dave Hansen <dave.hansen@intel.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Matthew Wilcox <willy@infradead.org>,
	linux-mm <linux-mm@kvack.org>, Vlastimil Babka <vbabka@suse.cz>,
	Andrew Morton <akpm@linux-foundation.org>,
	Mel Gorman <mgorman@techsingularity.net>,
	linux-arm-kernel@lists.infradead.org,
	Oscar Salvador <osalvador@suse.de>,
	Yang Zhang <yang.zhang.wz@gmail.com>,
	Pankaj Gupta <pagupta@redhat.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Nitesh Narayan Lal <nitesh@redhat.com>,
	Rik van Riel <riel@surriel.com>,
	lcapitulino@redhat.com, "Wang, Wei W" <wei.w.wang@intel.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Alexander Duyck <alexander.h.duyck@linux.intel.com>
Subject: Re: [PATCH v10 0/6] mm / virtio: Provide support for unused page reporting
Date: Tue, 24 Sep 2019 10:07:11 -0700	[thread overview]
Message-ID: <CAKgT0UedoNBk3cp64SpCzXJqjtqBWZQSB7QzF7R_jhTDXbzNPg@mail.gmail.com> (raw)
In-Reply-To: <d2a7acdd-3bb9-05c9-42d0-70a500801cd6@redhat.com>

On Tue, Sep 24, 2019 at 8:32 AM David Hildenbrand <david@redhat.com> wrote:
>
> On 24.09.19 16:23, Michal Hocko wrote:
> > On Wed 18-09-19 10:52:25, Alexander Duyck wrote:
> > [...]
> >> 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.
> >>
> >> If another process needs to perform a massive manipulation of the free
> >> list, such as compaction, it can either reset a given individual boundary
> >> which will push the boundary back to the list_head, or it can clear the
> >> bit indicating the zone is actively processing which will result in the
> >> reporting process resetting all of the boundaries for a given zone.
> >
> > Is this any different from the previous version? The last review
> > feedback (both from me and Mel) was that we are not happy to have an
> > externally imposed constrains on how the page allocator is supposed to
> > maintain its free lists.
> >
> > If this is really the only way to go forward then I would like to hear
> > very convincing arguments about other approaches not being feasible.
>
> Adding to what Alexander said, I don't consider the other approaches
> (especially the bitmap-based approach Nitesh is currently working on)
> infeasible. There might be more rough edges (e.g., sparse zones) and
> eventually sometimes a little more work to be done, but definitely
> feasible. Incorporating stuff into the buddy might make some tasks
> (e.g., identify free pages) more efficient.
>
> I still somewhat like the idea of capturing hints of free pages (in
> whatever data structure) and then going over the hints, seeing if the
> pages are still free. Then only temporarily isolating the still-free
> pages, reporting them, and un-isolating them after they were reported. I
> like the idea that the pages are not fake-allocated but only temporarily
> blocked. That works nicely e.g., with the movable zone (contain only
> movable data).

One other change in this patch set is that I split the headers so that
there is an internal header that resides in the mm tree and an
external one that provides the page reporting device structure and the
register/unregister functions. All that virtio-balloon knows is that
it is registering a notifier and will be called with scatter gather
lists for memory that is not currently in use by the kernel. It has no
visibility into the internal free_areas or the current state of the
buddy allocator. Rather than having two blocks that are both trying to
maintain that state, I have consolidated it all into the buddy
allocator with page reporting.

> But anyhow, after decades of people working on free page
> hinting/reporting, I am happy with anything that gets accepted upstream :D

Agreed. After working on this for 9 months I would be happy to get
something upstream that addresses this.

- Alex

  parent reply	other threads:[~2019-09-24 17:07 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-18 17:52 Alexander Duyck
2019-09-18 17:52 ` [PATCH v10 1/6] mm: Adjust shuffle code to allow for future coalescing Alexander Duyck
2019-09-18 17:52 ` [PATCH v10 2/6] mm: Use zone and order instead of free area in free_list manipulators Alexander Duyck
2019-09-18 17:52 ` [PATCH v10 3/6] mm: Introduce Reported pages Alexander Duyck
2019-09-21 15:25   ` [mm] 0f5b256b2c: will-it-scale.per_process_ops -1.2% regression kernel test robot
2019-09-23  8:15   ` [PATCH v10 3/6] mm: Introduce Reported pages Michael S. Tsirkin
2019-09-23 14:50     ` Alexander Duyck
2019-09-23 15:00       ` Michael S. Tsirkin
2019-09-23 15:28         ` Alexander Duyck
2019-09-23 15:37           ` Michael S. Tsirkin
2019-09-23 15:45             ` David Hildenbrand
2019-09-23 15:47               ` David Hildenbrand
2019-09-23 15:50                 ` Michael S. Tsirkin
2019-09-23 15:53                   ` David Hildenbrand
2019-09-23 15:49               ` Michael S. Tsirkin
2019-09-23 16:39               ` Alexander Duyck
2019-09-18 17:52 ` [PATCH v10 4/6] mm: Add device side and notifier for unused page reporting Alexander Duyck
2019-09-18 17:53 ` [PATCH v10 5/6] virtio-balloon: Pull page poisoning config out of free page hinting Alexander Duyck
2019-09-18 17:58   ` Michael S. Tsirkin
2019-09-18 18:05     ` Alexander Duyck
2019-09-18 17:53 ` [PATCH v10 6/6] virtio-balloon: Add support for providing unused page reports to host Alexander Duyck
2019-09-18 17:53 ` [PATCH v10 QEMU 1/3] virtio-ballon: Implement support for page poison tracking feature Alexander Duyck
2019-09-18 17:53 ` [PATCH v10 QEMU 2/3] virtio-balloon: Add bit to notify guest of unused page reporting Alexander Duyck
2019-09-18 17:53 ` [PATCH v10 QEMU 3/3] virtio-balloon: Provide a interface for " Alexander Duyck
2019-09-24 14:23 ` [PATCH v10 0/6] mm / virtio: Provide support " Michal Hocko
2019-09-24 15:20   ` Alexander Duyck
2019-09-26 12:22     ` Michal Hocko
2019-09-26 15:13       ` Alexander Duyck
2019-09-24 15:32   ` David Hildenbrand
2019-09-24 15:51     ` Nitesh Narayan Lal
2019-09-24 17:07     ` Alexander Duyck [this message]
2019-09-24 17:28       ` David Hildenbrand

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