[Xen-devel] [PATCH 3 of 3] PoD, hap: Fix logdirty mode when using hardware assisted paging

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

# HG changeset patch
# User George Dunlap <george.dunlap@xxxxxxxxxxxxx>
# Date 1295274541 0
# Node ID dd81c7acd9b323e9d2e4e3a41b81783fc7df5342
# Parent  55e123a24da84f3b83caa7a7332699df73aaa90d
PoD,hap: Fix logdirty mode when using hardware assisted paging

When writing a writable p2m entry for a pfn, we need to mark the pfn
dirty to avoid corruption when doing live migration.

Marking the page dirty exposes another issue, where there are
excessive sweeps for zero pages if there's a mismatch between PoD
entries and cache entries.  Only sweep for zero pages if we actually
need more memory.

Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>

diff -r 55e123a24da8 -r dd81c7acd9b3 xen/arch/x86/mm/p2m.c
--- a/xen/arch/x86/mm/p2m.c     Mon Jan 17 14:24:13 2011 +0000
+++ b/xen/arch/x86/mm/p2m.c     Mon Jan 17 14:29:01 2011 +0000
@@ -1142,14 +1142,22 @@
         return 0;
     }
 
-    /* If we're low, start a sweep */
-    if ( order == 9 && page_list_empty(&p2m->pod.super) )
-        p2m_pod_emergency_sweep_super(p2m);
-
-    if ( page_list_empty(&p2m->pod.single) &&
-         ( ( order == 0 )
-           || (order == 9 && page_list_empty(&p2m->pod.super) ) ) )
-        p2m_pod_emergency_sweep(p2m);
+    /* Once we've ballooned down enough that we can fill the remaining
+     * PoD entries from the cache, don't sweep even if the particular
+     * list we want to use is empty: that can lead to thrashing zero pages 
+     * through the cache for no good reason.  */
+    if ( p2m->pod.entry_count > p2m->pod.count )
+    {
+
+        /* If we're low, start a sweep */
+        if ( order == 9 && page_list_empty(&p2m->pod.super) )
+            p2m_pod_emergency_sweep_super(p2m);
+
+        if ( page_list_empty(&p2m->pod.single) &&
+             ( ( order == 0 )
+               || (order == 9 && page_list_empty(&p2m->pod.super) ) ) )
+            p2m_pod_emergency_sweep(p2m);
+    }
 
     /* Keep track of the highest gfn demand-populated by a guest fault */
     if ( q == p2m_guest && gfn > p2m->pod.max_guest )
@@ -1176,7 +1184,10 @@
     set_p2m_entry(p2m, gfn_aligned, mfn, order, p2m_ram_rw, 
p2m->default_access);
 
     for( i = 0; i < (1UL << order); i++ )
+    {
         set_gpfn_from_mfn(mfn_x(mfn) + i, gfn_aligned + i);
+        paging_mark_dirty(d, mfn_x(mfn) + i);
+    }
     
     p2m->pod.entry_count -= (1 << order); /* Lock: p2m */
     BUG_ON(p2m->pod.entry_count < 0);

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