From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wei Liu Subject: Re: [PATCH] libxc: try to find last used pfn when migrating Date: Fri, 27 Nov 2015 15:33:25 +0000 Message-ID: <20151127153325.GC21588@citrix.com> References: <1448635853-24865-1-git-send-email-jgross@suse.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <1448635853-24865-1-git-send-email-jgross@suse.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Juergen Gross Cc: wei.liu2@citrix.com, Ian.Campbell@citrix.com, stefano.stabellini@eu.citrix.com, andrew.cooper3@citrix.com, ian.jackson@eu.citrix.com, xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org On Fri, Nov 27, 2015 at 03:50:53PM +0100, Juergen Gross wrote: > For migration the last used pfn of a guest is needed to size the > logdirty bitmap and as an upper bound of the page loop. Unfortunately > there are pv-kernels advertising a much higher maximum pfn as they > are really using in order to support memory hotplug. This will lead > to allocation of much more memory in Xen tools during migration as > really needed. > > Try to find the last used guest pfn of a pv-domu by scanning the p2m > tree from the last entry towards it's start and search for an entry > not being invalid. > > Normally the mid pages of the p2m tree containing all invalid entries > are being reused, so we can just scan the top page for identical > entries and skip them but the first one. > > Signed-off-by: Juergen Gross > --- > tools/libxc/xc_sr_save.c | 8 ++++---- > tools/libxc/xc_sr_save_x86_pv.c | 34 +++++++++++++++++++++++++++++++--- > 2 files changed, 35 insertions(+), 7 deletions(-) > > diff --git a/tools/libxc/xc_sr_save.c b/tools/libxc/xc_sr_save.c > index 0c12e56..22b3f18 100644 > --- a/tools/libxc/xc_sr_save.c > +++ b/tools/libxc/xc_sr_save.c > @@ -677,6 +677,10 @@ static int setup(struct xc_sr_context *ctx) > DECLARE_HYPERCALL_BUFFER_SHADOW(unsigned long, dirty_bitmap, > &ctx->save.dirty_bitmap_hbuf); > > + rc = ctx->save.ops.setup(ctx); > + if ( rc ) > + goto err; > + > dirty_bitmap = xc_hypercall_buffer_alloc_pages( > xch, dirty_bitmap, NRPAGES(bitmap_size(ctx->save.p2m_size))); > ctx->save.batch_pfns = malloc(MAX_BATCH_SIZE * > @@ -692,10 +696,6 @@ static int setup(struct xc_sr_context *ctx) > goto err; > } > p2m_size is set in two places for PV guest. Since we are now relying on ops.setup to set p2m_size, the invocation to xc_domain_nr_gpfns in xc_domain_save should be removed, so that we only have one place to set p2m_size. You then also need to call xc_domain_nr_gpfns in HVM's ops.setup (x86_hvm_setup). Wei.