KVM Archive on lore.kernel.org
 help / color / Atom feed
From: Nitesh Narayan Lal <nitesh@redhat.com>
To: Alexander Duyck <alexander.duyck@gmail.com>,
	David Hildenbrand <david@redhat.com>
Cc: kvm list <kvm@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>,
	virtio-dev@lists.oasis-open.org,
	Paolo Bonzini <pbonzini@redhat.com>,
	lcapitulino@redhat.com, pagupta@redhat.com, wei.w.wang@intel.com,
	Yang Zhang <yang.zhang.wz@gmail.com>,
	Rik van Riel <riel@surriel.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	dodgen@google.com, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	dhildenb@redhat.com, Andrea Arcangeli <aarcange@redhat.com>,
	john.starks@microsoft.com, Dave Hansen <dave.hansen@intel.com>,
	Michal Hocko <mhocko@suse.com>,
	cohuck@redhat.com
Subject: Re: [RFC][Patch v12 1/2] mm: page_reporting: core infrastructure
Date: Tue, 20 Aug 2019 10:11:45 -0400
Message-ID: <c0e3a4dd-3eab-f00d-6a87-272bb9481dd1@redhat.com> (raw)
In-Reply-To: <b5d4ee25-ae3e-f012-d7f2-7a27d7bbcc54@redhat.com>


On 8/12/19 4:04 PM, Nitesh Narayan Lal wrote:
> On 8/12/19 2:47 PM, Alexander Duyck wrote:
>> On Mon, Aug 12, 2019 at 6:13 AM Nitesh Narayan Lal <nitesh@redhat.com> wrote:
>>> This patch introduces the core infrastructure for free page reporting in
>>> virtual environments. It enables the kernel to track the free pages which
>>> can be reported to its hypervisor so that the hypervisor could
>>> free and reuse that memory as per its requirement.
>>>
>>> While the pages are getting processed in the hypervisor (e.g.,
>>> via MADV_DONTNEED), the guest must not use them, otherwise, data loss
>>> would be possible. To avoid such a situation, these pages are
>>> temporarily removed from the buddy. The amount of pages removed
>>> temporarily from the buddy is governed by the backend(virtio-balloon
>>> in our case).
>>>
>>> To efficiently identify free pages that can to be reported to the
>>> hypervisor, bitmaps in a coarse granularity are used. Only fairly big
>>> chunks are reported to the hypervisor - especially, to not break up THP
>>> in the hypervisor - "MAX_ORDER - 2" on x86, and to save space. The bits
>>> in the bitmap are an indication whether a page *might* be free, not a
>>> guarantee. A new hook after buddy merging sets the bits.
>>>
>>> Bitmaps are stored per zone, protected by the zone lock. A workqueue
>>> asynchronously processes the bitmaps, trying to isolate and report pages
>>> that are still free. The backend (virtio-balloon) is responsible for
>>> reporting these batched pages to the host synchronously. Once reporting/
>>> freeing is complete, isolated pages are returned back to the buddy.
>>>
>>> Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>
>> So if I understand correctly the hotplug support for this is still not
>> included correct? 
>
> That is correct, I have it as an ongoing-item in my cover-email.
> In case, we decide to go with this approach do you think it is a blocker?

I am planning to defer memory hotplug/hotremove support for the future. Due to
following reasons:
* I would like to first get a basic framework ready and merged (in case we
  decide to go ahead with this approach) and then build on top of it.
* Memory hotplug/hotremove is not a primary use case in our mind right now and
  hence I am not considering this as a blocker for the first step.

Following are the items which I intend to address before my next submission:
* Use zone flag and reference counter to track the number of zones requesting
  page reporting.
* Move the bitmap and its respective fields into a structure whose rcu-protected
  pointer object is maintained on a per-zone basis.
* Pick Alexander's patch for page poisoning support and test them with my patch
  set. (@Alexander: I will keep your signed-off for these patches to indicate
  you are the original author, please do let me know there is a better way to
  give credit).
* Address other suggestions/comments received on v12.

Looking forward to any suggestions/comments.


[...]
> +
> +       /* assign the configuration object provided by the backend */
> +       rcu_assign_pointer(page_reporting_conf, phconf);
> +
> +out:
> +       mutex_unlock(&page_reporting_mutex);
> +       return ret;
> +}
> +EXPORT_SYMBOL_GPL(page_reporting_enable);
> --
> 2.21.0
>
-- 
Thanks
Nitesh


  reply index

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-12 13:12 [RFC][PATCH v12 0/2] mm: Support for page reporting Nitesh Narayan Lal
2019-08-12 13:12 ` [RFC][Patch v12 1/2] mm: page_reporting: core infrastructure Nitesh Narayan Lal
2019-08-12 18:47   ` Alexander Duyck
2019-08-12 20:04     ` Nitesh Narayan Lal
2019-08-20 14:11       ` Nitesh Narayan Lal [this message]
2019-08-12 20:05     ` David Hildenbrand
2019-08-13 10:30       ` Nitesh Narayan Lal
2019-08-13 10:34         ` David Hildenbrand
2019-08-13 10:42           ` Nitesh Narayan Lal
2019-08-13 10:44             ` David Hildenbrand
2019-08-13 23:14           ` Alexander Duyck
2019-08-14  7:07             ` David Hildenbrand
2019-08-14 12:49               ` [virtio-dev] " Nitesh Narayan Lal
2019-08-14 15:49     ` Nitesh Narayan Lal
2019-08-14 16:11       ` Alexander Duyck
2019-08-15 13:15         ` Nitesh Narayan Lal
2019-08-15 19:22           ` Nitesh Narayan Lal
2019-08-15 23:00             ` Alexander Duyck
2019-08-16 18:35               ` Nitesh Narayan Lal
2019-08-30 15:15     ` Nitesh Narayan Lal
2019-08-30 15:31       ` Alexander Duyck
2019-08-30 16:05         ` Nitesh Narayan Lal
2019-09-04  8:40           ` [virtio-dev] " David Hildenbrand
2019-10-10 20:36   ` Alexander Duyck
2019-10-11 11:02     ` Nitesh Narayan Lal
2019-08-12 13:12 ` [RFC][Patch v12 2/2] virtio-balloon: interface to support free page reporting Nitesh Narayan Lal
2019-08-14 10:29   ` Cornelia Huck
2019-08-14 11:47     ` Nitesh Narayan Lal
2019-08-14 13:42       ` Cornelia Huck
2019-08-14 14:01         ` Nitesh Narayan Lal
2019-08-12 13:13 ` [QEMU Patch 1/2] virtio-balloon: adding bit for page reporting support Nitesh Narayan Lal
2019-08-12 13:13   ` [QEMU Patch 2/2] virtio-balloon: support for handling page reporting Nitesh Narayan Lal
2019-08-12 15:18     ` Alexander Duyck
2019-08-12 15:26       ` Nitesh Narayan Lal
2019-09-11 12:30 ` [RFC][PATCH v12 0/2] mm: Support for " David Hildenbrand

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=c0e3a4dd-3eab-f00d-6a87-272bb9481dd1@redhat.com \
    --to=nitesh@redhat.com \
    --cc=aarcange@redhat.com \
    --cc=alexander.duyck@gmail.com \
    --cc=cohuck@redhat.com \
    --cc=dave.hansen@intel.com \
    --cc=david@redhat.com \
    --cc=dhildenb@redhat.com \
    --cc=dodgen@google.com \
    --cc=john.starks@microsoft.com \
    --cc=konrad.wilk@oracle.com \
    --cc=kvm@vger.kernel.org \
    --cc=lcapitulino@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=mhocko@suse.com \
    --cc=mst@redhat.com \
    --cc=pagupta@redhat.com \
    --cc=pbonzini@redhat.com \
    --cc=riel@surriel.com \
    --cc=virtio-dev@lists.oasis-open.org \
    --cc=wei.w.wang@intel.com \
    --cc=yang.zhang.wz@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

KVM Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/kvm/0 kvm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 kvm kvm/ https://lore.kernel.org/kvm \
		kvm@vger.kernel.org
	public-inbox-index kvm

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.kvm


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git