[Xen-changelog] [xen-unstable] xenpaging: handle temporary out-of-memory conditions during page-in

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir@xxxxxxx>
# Date 1290781411 0
# Node ID 08158f001f19d158c523cb14c39e354a805e7e65
# Parent  c7b08fc1cb8df8e3f3ccf719a1a62bd8157472de
xenpaging: handle temporary out-of-memory conditions during page-in

p2m_mem_paging_prep() should return -ENOMEM if a new page could not be
allocated. This can be handled in xenpaging to retry the
page-in. Right now such condition would stall the guest because the
requested page will not come back, xenpaging simply exits. So
xenpaging could very well retry the allocation forever to rescue the
guest.

Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>
---
 tools/xenpaging/xenpaging.c |   33 +++++++++++++++++++++++----------
 xen/arch/x86/mm/p2m.c       |    2 +-
 2 files changed, 24 insertions(+), 11 deletions(-)

diff -r c7b08fc1cb8d -r 08158f001f19 tools/xenpaging/xenpaging.c
--- a/tools/xenpaging/xenpaging.c       Fri Nov 26 14:22:38 2010 +0000
+++ b/tools/xenpaging/xenpaging.c       Fri Nov 26 14:23:31 2010 +0000
@@ -26,6 +26,7 @@
 #include <stdarg.h>
 #include <time.h>
 #include <signal.h>
+#include <unistd.h>
 #include <xc_private.h>
 
 #include <xen/mem_event.h>
@@ -415,19 +416,31 @@ static int xenpaging_populate_page(
     unsigned long _gfn;
     void *page;
     int ret;
-
-    /* Tell Xen to allocate a page for the domain */
-    ret = xc_mem_paging_prep(paging->xc_handle, paging->mem_event.domain_id,
-                             *gfn);
-    if ( ret != 0 )
-    {
-        ERROR("Error preparing for page in");
-        goto out_map;
-    }
+    unsigned char oom = 0;
+
+    _gfn = *gfn;
+    do
+    {
+        /* Tell Xen to allocate a page for the domain */
+        ret = xc_mem_paging_prep(paging->xc_handle, 
paging->mem_event.domain_id,
+                                 _gfn);
+        if ( ret != 0 )
+        {
+            if ( errno == ENOMEM )
+            {
+                if ( oom++ == 0 )
+                    DPRINTF("ENOMEM while preparing gfn %lx\n", _gfn);
+                sleep(1);
+                continue;
+            }
+            ERROR("Error preparing for page in");
+            goto out_map;
+        }
+    }
+    while ( ret && !interrupted );
 
     /* Map page */
     ret = -EFAULT;
-    _gfn = *gfn;
     page = xc_map_foreign_pages(paging->xc_handle, paging->mem_event.domain_id,
                                 PROT_READ | PROT_WRITE, &_gfn, 1);
     *gfn = _gfn;
diff -r c7b08fc1cb8d -r 08158f001f19 xen/arch/x86/mm/p2m.c
--- a/xen/arch/x86/mm/p2m.c     Fri Nov 26 14:22:38 2010 +0000
+++ b/xen/arch/x86/mm/p2m.c     Fri Nov 26 14:23:31 2010 +0000
@@ -2802,7 +2802,7 @@ int p2m_mem_paging_prep(struct p2m_domai
     /* Get a free page */
     page = alloc_domheap_page(p2m->domain, 0);
     if ( unlikely(page == NULL) )
-        return -EINVAL;
+        return -ENOMEM;
 
     /* Fix p2m mapping */
     p2m_lock(p2m);

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