RE: [PATCH v2 repost 4/7] virtio-balloon: speed up inflate/deflate process

From	"Li, Liang Z" <liang.z.li@intel.com>
Newsgroups	linux.kernel
Subject	RE: [PATCH v2 repost 4/7] virtio-balloon: speed up inflate/deflate process
Date	2016-07-29 02:40 +0200
Message-ID	<s040h-5qP-5@gated-at.bofh.it> (permalink)
References	<rZlZf-1d6-3@gated-at.bofh.it> <rZlZf-1d6-1@gated-at.bofh.it> <rZEIy-4S2-7@gated-at.bofh.it> <rZJRV-h8-41@gated-at.bofh.it> <s01OO-40K-15@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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> 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

Thread

[PATCH v2 repost 4/7] virtio-balloon: speed up inflate/deflate process Liang Li <liang.z.li@intel.com> - 2016-07-27 03:40 +0200
  Re: [PATCH v2 repost 4/7] virtio-balloon: speed up inflate/deflate  process Dave Hansen <dave.hansen@intel.com> - 2016-07-27 18:10 +0200
    Re: [PATCH v2 repost 4/7] virtio-balloon: speed up inflate/deflate  process "Michael S. Tsirkin" <mst@redhat.com> - 2016-07-27 23:40 +0200
      RE: [PATCH v2 repost 4/7] virtio-balloon: speed up inflate/deflate  process "Li, Liang Z" <liang.z.li@intel.com> - 2016-07-28 05:40 +0200
        Re: [PATCH v2 repost 4/7] virtio-balloon: speed up inflate/deflate  process "Michael S. Tsirkin" <mst@redhat.com> - 2016-07-29 00:20 +0200
          RE: [virtio-dev] Re: [PATCH v2 repost 4/7] virtio-balloon: speed up  inflate/deflate process "Li, Liang Z" <liang.z.li@intel.com> - 2016-07-29 03:10 +0200
    RE: [PATCH v2 repost 4/7] virtio-balloon: speed up inflate/deflate  process "Li, Liang Z" <liang.z.li@intel.com> - 2016-07-28 03:20 +0200
      Re: [PATCH v2 repost 4/7] virtio-balloon: speed up inflate/deflate  process "Michael S. Tsirkin" <mst@redhat.com> - 2016-07-28 03:50 +0200
        RE: [virtio-dev] Re: [PATCH v2 repost 4/7] virtio-balloon: speed up  inflate/deflate process "Li, Liang Z" <liang.z.li@intel.com> - 2016-07-28 08:40 +0200
          Re: [virtio-dev] Re: [PATCH v2 repost 4/7] virtio-balloon: speed up  inflate/deflate process "Michael S. Tsirkin" <mst@redhat.com> - 2016-07-29 00:00 +0200
            RE: [virtio-dev] Re: [PATCH v2 repost 4/7] virtio-balloon: speed up  inflate/deflate process "Li, Liang Z" <liang.z.li@intel.com> - 2016-07-29 02:50 +0200
            Re: [virtio-dev] Re: [PATCH v2 repost 4/7] virtio-balloon: speed up  inflate/deflate process Dave Hansen <dave.hansen@intel.com> - 2016-07-29 21:50 +0200
              RE: [virtio-dev] Re: [PATCH v2 repost 4/7] virtio-balloon: speed up  inflate/deflate process "Li, Liang Z" <liang.z.li@intel.com> - 2016-08-02 02:40 +0200
  Re: [PATCH v2 repost 4/7] virtio-balloon: speed up inflate/deflate  process "Michael S. Tsirkin" <mst@redhat.com> - 2016-07-27 23:40 +0200
    RE: [PATCH v2 repost 4/7] virtio-balloon: speed up inflate/deflate  process "Li, Liang Z" <liang.z.li@intel.com> - 2016-07-28 05:10 +0200
      Re: [PATCH v2 repost 4/7] virtio-balloon: speed up inflate/deflate  process "Michael S. Tsirkin" <mst@redhat.com> - 2016-07-29 00:20 +0200
        RE: [PATCH v2 repost 4/7] virtio-balloon: speed up inflate/deflate  process "Li, Liang Z" <liang.z.li@intel.com> - 2016-07-29 02:40 +0200
  Re: [PATCH v2 repost 4/7] virtio-balloon: speed up inflate/deflate  process "Michael S. Tsirkin" <mst@redhat.com> - 2016-07-28 00:10 +0200
    RE: [PATCH v2 repost 4/7] virtio-balloon: speed up inflate/deflate  process "Li, Liang Z" <liang.z.li@intel.com> - 2016-07-28 05:50 +0200

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