[Xen-devel] [PATCH] tools/libxc: Batch memory allocations for PV guests

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

The current code for allocating memory for PV guests batches the
hypercalls to allocate memory by allocating 1024*1024 extents of order 0
at a time. To make this faster, first try allocating single extents of
order 9 (2 MiB) before falling back to the order 0 allocating if the
order 9 allocation fails.

On my test machine this reduced the time to start a 128 GiB PV guest by
about 60 seconds.

Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
---
 tools/libxc/xc_dom_x86.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/tools/libxc/xc_dom_x86.c b/tools/libxc/xc_dom_x86.c
index 783f749..a674d39 100644
--- a/tools/libxc/xc_dom_x86.c
+++ b/tools/libxc/xc_dom_x86.c
@@ -761,7 +761,7 @@ int arch_setup_meminit(struct xc_dom_image *dom)
 {
     int rc;
     xen_pfn_t pfn, allocsz, mfn, total, pfn_base;
-    int i, j;
+    int i, j, k;
 
     rc = x86_compat(dom->xch, dom->guest_domid, dom->guest_type);
     if ( rc )
@@ -881,7 +881,25 @@ int arch_setup_meminit(struct xc_dom_image *dom)
             for ( pfn = pfn_base; pfn < pfn_base+pages; pfn++ )
                 dom->p2m_host[pfn] = pfn;
 
-            for ( j = 0; j < pages; j += allocsz )
+            for ( j = 0; j < pages; )
+            {
+                if ( (pages - j) < SUPERPAGE_NR_PFNS )
+                    break;
+
+                mfn = dom->p2m_host[pfn_base + j];
+                rc = xc_domain_populate_physmap(dom->xch, dom->guest_domid, 1,
+                         SUPERPAGE_PFN_SHIFT, memflags, &mfn);
+
+                if ( rc != 1 )
+                    break;
+
+                /* Expand the returned mfn into the p2m array */
+                for ( k = 0; k < SUPERPAGE_NR_PFNS; k++, j++ )
+                    dom->p2m_host[pfn_base + j] = mfn + k;
+            }
+
+            rc = 0;
+            for ( ; j < pages; j += allocsz )
             {
                 allocsz = pages - j;
                 if ( allocsz > 1024*1024 )
-- 
2.1.0


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