[Xen-devel] [PATCH] don't save Xen heap pages during domain save

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

As discussed in the thread starting at
http://lists.xensource.com/archives/html/xen-devel/2010-05/msg01383.html,
don't save Xen heap pages in order to avoid overallocation when the
domain gets restored, as those pages would get (temporarily) backed
with normal RAM pages by the restore code.

This requires making DOMCTL_getpageframeinfo{2,3} usable for HVM guests,
meaning that the input to these must be treated as GMFNs.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

--- 2010-06-15.orig/tools/libxc/xc_domain_save.c        2010-06-01 
13:39:57.000000000 +0200
+++ 2010-06-15/tools/libxc/xc_domain_save.c     2010-06-15 09:32:42.000000000 
+0200
@@ -1288,58 +1288,64 @@ int xc_domain_save(xc_interface *xch, in
                 goto out;
             }
 
-            if ( hvm )
+            /* Get page types */
+            if ( xc_get_pfn_type_batch(xch, dom, batch, pfn_type) )
             {
-                /* Look for and skip completely empty batches. */
-                for ( j = 0; j < batch; j++ )
-                {
-                    if ( !pfn_err[j] )
-                        break;
-                    pfn_type[j] |= XEN_DOMCTL_PFINFO_XTAB;
-                }
-                if ( j == batch )
-                {
-                    munmap(region_base, batch*PAGE_SIZE);
-                    continue; /* bail on this batch: no valid pages */
-                }
-                for ( ; j < batch; j++ )
-                    if ( pfn_err[j] )
-                        pfn_type[j] |= XEN_DOMCTL_PFINFO_XTAB;
+                PERROR("get_pfn_type_batch failed");
+                goto out;
             }
-            else
+
+            for ( run = j = 0; j < batch; j++ )
             {
-                /* Get page types */
-                if ( xc_get_pfn_type_batch(xch, dom, batch, pfn_type) )
-                {
-                    PERROR("get_pfn_type_batch failed");
-                    goto out;
-                }
+                unsigned long gmfn = pfn_batch[j];
 
-                for ( j = 0; j < batch; j++ )
+                if ( !hvm )
+                    gmfn = pfn_to_mfn(gmfn);
+
+                if ( pfn_err[j] )
                 {
-                    unsigned long mfn = pfn_to_mfn(pfn_batch[j]);
-                    
                     if ( pfn_type[j] == XEN_DOMCTL_PFINFO_XTAB )
-                    {
-                        DPRINTF("type fail: page %i mfn %08lx\n", 
-                                j, mfn);
                         continue;
-                    }
-                    
-                    if ( debug )
+                    DPRINTF("map fail: page %i mfn %08lx err %d\n",
+                            j, gmfn, pfn_err[j]);
+                    pfn_type[j] = XEN_DOMCTL_PFINFO_XTAB;
+                    continue;
+                }
+
+                if ( pfn_type[j] == XEN_DOMCTL_PFINFO_XTAB )
+                {
+                    DPRINTF("type fail: page %i mfn %08lx\n", j, gmfn);
+                    continue;
+                }
+
+                /* canonicalise mfn->pfn */
+                pfn_type[j] |= pfn_batch[j];
+                ++run;
+
+                if ( debug )
+                {
+                    if ( hvm )
+                        DPRINTF("%d pfn=%08lx sum=%08lx\n",
+                                iter,
+                                pfn_type[j],
+                                csum_page(region_base + (PAGE_SIZE*j)));
+                    else
                         DPRINTF("%d pfn= %08lx mfn= %08lx [mfn]= %08lx"
                                 " sum= %08lx\n",
                                 iter,
-                                pfn_type[j] | pfn_batch[j],
-                                mfn,
-                                mfn_to_pfn(mfn),
+                                pfn_type[j],
+                                gmfn,
+                                mfn_to_pfn(gmfn),
                                 csum_page(region_base + (PAGE_SIZE*j)));
-                    
-                    /* canonicalise mfn->pfn */
-                    pfn_type[j] |= pfn_batch[j];
                 }
             }
 
+            if ( !run )
+            {
+                munmap(region_base, batch*PAGE_SIZE);
+                continue; /* bail on this batch: no valid pages */
+            }
+
             if ( wrexact(io_fd, &batch, sizeof(unsigned int)) )
             {
                 PERROR("Error when writing to state file (2)");
--- 2010-06-15.orig/xen/arch/x86/domctl.c       2010-03-02 09:11:28.000000000 
+0100
+++ 2010-06-15/xen/arch/x86/domctl.c    2010-06-15 09:32:42.000000000 +0200
@@ -207,11 +207,12 @@ long arch_do_domctl(
 
                 for ( j = 0; j < k; j++ )
                 {
-                    unsigned long type = 0, mfn = arr[j];
+                    unsigned long type = 0, mfn = gmfn_to_mfn(d, arr[j]);
 
                     page = mfn_to_page(mfn);
 
-                    if ( unlikely(!mfn_valid(mfn)) )
+                    if ( unlikely(!mfn_valid(mfn)) ||
+                         unlikely(is_xen_heap_mfn(mfn)) )
                         type = XEN_DOMCTL_PFINFO_XTAB;
                     else if ( xsm_getpageframeinfo(page) != 0 )
                         ;
@@ -306,14 +307,15 @@ long arch_do_domctl(
             for ( j = 0; j < k; j++ )
             {      
                 struct page_info *page;
-                unsigned long mfn = arr32[j];
+                unsigned long mfn = gmfn_to_mfn(d, arr32[j]);
 
                 page = mfn_to_page(mfn);
 
                 if ( domctl->cmd == XEN_DOMCTL_getpageframeinfo3)
                     arr32[j] = 0;
 
-                if ( unlikely(!mfn_valid(mfn)) )
+                if ( unlikely(!mfn_valid(mfn)) ||
+                     unlikely(is_xen_heap_mfn(mfn)) )
                     arr32[j] |= XEN_DOMCTL_PFINFO_XTAB;
                 else if ( xsm_getpageframeinfo(page) != 0 )
                     continue;

Attachment: dont-save-xen-heap-pages.patch
Description: Text document

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