From: "Li, Liang Z" <liang.z.li@intel.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"virtualization@lists.linux-foundation.org"
<virtualization@lists.linux-foundation.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"virtio-dev@lists.oasis-open.org"
<virtio-dev@lists.oasis-open.org>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
"dgilbert@redhat.com" <dgilbert@redhat.com>,
"quintela@redhat.com" <quintela@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
"Vlastimil Babka" <vbabka@suse.cz>,
Mel Gorman <mgorman@techsingularity.net>,
"Paolo Bonzini" <pbonzini@redhat.com>,
Cornelia Huck <cornelia.huck@de.ibm.com>,
Amit Shah <amit.shah@redhat.com>
Subject: RE: [PATCH v2 repost 4/7] virtio-balloon: speed up inflate/deflate process
Date: Fri, 29 Jul 2016 00:38:18 +0000 [thread overview]
Message-ID: <F2CBF3009FA73547804AE4C663CAB28E04214BD3@shsmsx102.ccr.corp.intel.com> (raw)
In-Reply-To: <20160729011553-mutt-send-email-mst@kernel.org>
> On Thu, Jul 28, 2016 at 03:06:37AM +0000, Li, Liang Z wrote:
> > > > + * VIRTIO_BALLOON_PFNS_LIMIT is used to limit the size of page
> > > > +bitmap
> > > > + * to prevent a very large page bitmap, there are two reasons for this:
> > > > + * 1) to save memory.
> > > > + * 2) allocate a large bitmap may fail.
> > > > + *
> > > > + * The actual limit of pfn is determined by:
> > > > + * pfn_limit = min(max_pfn, VIRTIO_BALLOON_PFNS_LIMIT);
> > > > + *
> > > > + * If system has more pages than VIRTIO_BALLOON_PFNS_LIMIT, we
> > > > +will scan
> > > > + * the page list and send the PFNs with several times. To reduce
> > > > +the
> > > > + * overhead of scanning the page list. VIRTIO_BALLOON_PFNS_LIMIT
> > > > +should
> > > > + * be set with a value which can cover most cases.
> > >
> > > So what if it covers 1/32 of the memory? We'll do 32 exits and not
> > > 1, still not a big deal for a big guest.
> > >
> >
> > The issue here is the overhead is too high for scanning the page list for 32
> times.
> > Limit the page bitmap size to a fixed value is better for a big guest?
> >
>
> I'd say avoid scanning free lists completely. Scan pages themselves and check
> the refcount to see whether they are free.
> This way each page needs to be tested once.
>
> And skip the whole optimization if less than e.g. 10% is free.
That's better than rescanning the free list. Will change in next version.
Thanks!
Liang
next prev parent reply other threads:[~2016-07-29 0:38 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-27 1:23 [PATCH v2 repost 0/7] Extend virtio-balloon for fast (de)inflating & fast live migration Liang Li
2016-07-27 1:23 ` [PATCH v2 repost 1/7] virtio-balloon: rework deflate to add page to a list Liang Li
2016-07-27 1:23 ` [PATCH v2 repost 2/7] virtio-balloon: define new feature bit and page bitmap head Liang Li
2016-07-27 1:23 ` [PATCH v2 repost 3/7] mm: add a function to get the max pfn Liang Li
2016-07-27 22:08 ` Michael S. Tsirkin
2016-07-27 22:52 ` Dave Hansen
2016-07-27 1:23 ` [PATCH v2 repost 4/7] virtio-balloon: speed up inflate/deflate process Liang Li
2016-07-27 16:03 ` Dave Hansen
2016-07-27 21:39 ` Michael S. Tsirkin
2016-07-28 3:30 ` Li, Liang Z
2016-07-28 22:15 ` Michael S. Tsirkin
2016-07-29 1:08 ` [virtio-dev] " Li, Liang Z
2016-07-28 1:13 ` Li, Liang Z
2016-07-28 1:45 ` Michael S. Tsirkin
2016-07-28 6:36 ` [virtio-dev] " Li, Liang Z
2016-07-28 21:51 ` Michael S. Tsirkin
2016-07-29 0:46 ` Li, Liang Z
2016-07-29 19:48 ` Dave Hansen
2016-08-02 0:28 ` Li, Liang Z
2016-07-27 21:36 ` Michael S. Tsirkin
2016-07-28 3:06 ` Li, Liang Z
2016-07-28 22:17 ` Michael S. Tsirkin
2016-07-29 0:38 ` Li, Liang Z [this message]
2016-07-27 22:07 ` Michael S. Tsirkin
2016-07-28 3:48 ` Li, Liang Z
2016-07-27 1:23 ` [PATCH v2 repost 5/7] virtio-balloon: define feature bit and head for misc virt queue Liang Li
2016-07-27 1:23 ` [PATCH v2 repost 6/7] mm: add the related functions to get free page info Liang Li
2016-07-27 16:40 ` Dave Hansen
2016-07-27 22:05 ` Michael S. Tsirkin
2016-07-27 22:16 ` Dave Hansen
2016-07-27 23:05 ` Michael S. Tsirkin
2016-07-28 4:36 ` Li, Liang Z
2016-07-28 0:10 ` Li, Liang Z
2016-07-28 0:17 ` Michael S. Tsirkin
2016-07-27 22:13 ` Michael S. Tsirkin
2016-07-28 5:30 ` [virtio-dev] " Li, Liang Z
2016-07-27 1:23 ` [PATCH v2 repost 7/7] virtio-balloon: tell host vm's " Liang Li
2016-07-27 22:00 ` Michael S. Tsirkin
2016-07-28 7:50 ` Li, Liang Z
2016-07-28 21:37 ` Michael S. Tsirkin
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