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From: Dave Hansen <dave.hansen@intel.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Alexander Duyck <alexander.duyck@gmail.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, rkrcmar@redhat.com,
	alexander.h.duyck@linux.intel.com, x86@kernel.org,
	mingo@redhat.com, bp@alien8.de, hpa@zytor.com,
	pbonzini@redhat.com, tglx@linutronix.de,
	akpm@linux-foundation.org
Subject: Re: [RFC PATCH 3/4] kvm: Add guest side support for free memory hints
Date: Mon, 11 Feb 2019 10:19:17 -0800
Message-ID: <d0610465-1655-1fd0-4847-7a6ba233df85@intel.com> (raw)
In-Reply-To: <20190211124925-mutt-send-email-mst@kernel.org>

On 2/11/19 9:58 AM, Michael S. Tsirkin wrote:
>>> Really it seems we want a virtio ring so we can pass a batch of these.
>>> E.g. 256 entries, 2M each - that's more like it.
>> That only makes sense for a system that's doing high-frequency,
>> discontiguous frees of 2M pages.  Right now, a 2M free/realloc cycle
>> (THP or hugetlb) is *not* super-high frequency just because of the
>> latency for zeroing the page.
> Heh but with a ton of free memory, and a thread zeroing some of
> it out in the background, will this still be the case?
> It could be that we'll be able to find clean pages
> at all times.

In a systems where we have some asynchrounous zeroing of memory where
freed, non-zeroed memory is sequestered out of the allocator, yeah, that
could make sense.

But, that's not what we have today.

>> A virtio ring seems like an overblown solution to a non-existent problem.
> It would be nice to see some traces to help us decide one way or the other.

Yeah, agreed.  Sounds like we need some more testing to see if these
approaches hit bottlenecks anywhere.

  reply index

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-04 18:15 [RFC PATCH 0/4] kvm: Report unused guest pages to host Alexander Duyck
2019-02-04 18:15 ` [RFC PATCH 1/4] madvise: Expose ability to set dontneed from kernel Alexander Duyck
2019-02-04 18:15 ` [RFC PATCH 2/4] kvm: Add host side support for free memory hints Alexander Duyck
2019-02-10  0:44   ` Michael S. Tsirkin
2019-02-11 17:34     ` Alexander Duyck
2019-02-11 17:36       ` Michael S. Tsirkin
2019-02-11 17:41     ` Dave Hansen
2019-02-11 17:48       ` Michael S. Tsirkin
2019-02-11 18:30         ` Alexander Duyck
2019-02-11 19:24           ` Michael S. Tsirkin
2019-02-04 18:15 ` [RFC PATCH 3/4] kvm: Add guest " Alexander Duyck
2019-02-04 19:44   ` Dave Hansen
2019-02-04 20:42     ` Alexander Duyck
2019-02-04 23:00   ` Nadav Amit
2019-02-04 23:37     ` Alexander Duyck
2019-02-05  0:03       ` Nadav Amit
2019-02-05  0:16         ` Alexander Duyck
2019-02-05  1:46           ` Nadav Amit
2019-02-05 18:09             ` Alexander Duyck
2019-02-07 18:21   ` Luiz Capitulino
2019-02-07 18:44     ` Alexander Duyck
2019-02-07 20:02       ` Luiz Capitulino
2019-02-08 21:05       ` Nitesh Narayan Lal
2019-02-08 21:31         ` Alexander Duyck
2019-02-10  0:49   ` Michael S. Tsirkin
2019-02-11 16:31     ` Alexander Duyck
2019-02-11 17:36       ` Michael S. Tsirkin
2019-02-11 18:10         ` Alexander Duyck
2019-02-11 19:54           ` Michael S. Tsirkin
2019-02-11 21:00             ` Alexander Duyck
2019-02-11 22:52               ` Michael S. Tsirkin
     [not found]                 ` <94462313ccd927d25675f69de459456cf066c1a2.camel@linux.intel.com>
2019-02-12  0:34                   ` Michael S. Tsirkin
2019-02-11 17:48     ` Dave Hansen
2019-02-11 17:58       ` Michael S. Tsirkin
2019-02-11 18:19         ` Dave Hansen [this message]
2019-02-11 19:56           ` Michael S. Tsirkin
2019-02-04 18:15 ` [RFC PATCH 4/4] mm: Add merge page notifier Alexander Duyck
2019-02-04 19:40   ` Dave Hansen
2019-02-04 19:51     ` Alexander Duyck
2019-02-10  0:57   ` Michael S. Tsirkin
2019-02-11 13:30     ` Nitesh Narayan Lal
2019-02-11 14:17       ` Michael S. Tsirkin
2019-02-11 16:24         ` Nitesh Narayan Lal
2019-02-11 17:41           ` Michael S. Tsirkin
2019-02-11 18:09             ` Nitesh Narayan Lal
2019-02-11  6:40   ` Aaron Lu
2019-02-11 15:58     ` Alexander Duyck
2019-02-12  2:09       ` Aaron Lu
2019-02-12 17:20         ` Alexander Duyck
2019-02-04 18:19 ` [RFC PATCH QEMU] i386/kvm: Enable paravirtual unused page hint mechanism Alexander Duyck
2019-02-05 17:25 ` [RFC PATCH 0/4] kvm: Report unused guest pages to host Nitesh Narayan Lal
2019-02-05 18:43   ` Alexander Duyck
2019-02-07 14:48 ` Nitesh Narayan Lal
2019-02-07 16:56   ` Alexander Duyck
2019-02-10  0:51 ` Michael S. Tsirkin

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