xenpaging: break endless loop during inital page-out with large pagefiles

To allow the starting for xenpaging right after 'xm start XYZ', I
specified a pagefile size equal to the guest memory size in the hope
to catch more errors where the paged-out state of a p2mt is not
checked.

While doing that, xenpaging got into an endless loop because some
pages cant be paged out right away. Now the policy reports an error if
the gfn number wraps.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Already-Acked-by: Patrick Colp <pjcolp@cs.ubc.ca>
Already-Acked-by: Keir Fraser <keir.fraser@citrix.com>

diff --git a/tools/xenpaging/policy_default.c b/tools/xenpaging/policy_default.c
index 1bb89e03ba75f2f12f91ad0e0c1fd0cbc33f7e79..5768e691e98c41d45ff012fe88b2afb06124f899 100644 (file)
--- a/tools/xenpaging/policy_default.c
+++ b/tools/xenpaging/policy_default.c
@@ -30,8 +30,12 @@
 
 
 static unsigned long mru[MRU_SIZE];
-static unsigned int i_mru = 0;
+static unsigned int i_mru;
 static unsigned long *bitmap;
+static unsigned long *unconsumed;
+static unsigned long current_gfn;
+static unsigned long bitmap_size;
+static unsigned long max_pages;
 
 
 int policy_init(xenpaging_t *paging)
@@ -41,9 +45,17 @@ int policy_init(xenpaging_t *paging)
 
     /* Allocate bitmap for pages not to page out */
     rc = alloc_bitmap(&bitmap, paging->bitmap_size);
+    if ( rc != 0 )
+        goto out;
+    /* Allocate bitmap to track unusable pages */
+    rc = alloc_bitmap(&unconsumed, paging->bitmap_size);
     if ( rc != 0 )
         goto out;
 
+    /* record bitmap_size */
+    bitmap_size = paging->bitmap_size;
+    max_pages = paging->domain_info->max_pages;
+
     /* Initialise MRU list of paged in pages */
     for ( i = 0; i < MRU_SIZE; i++ )
         mru[i] = INVALID_MFN;
@@ -51,8 +63,6 @@ int policy_init(xenpaging_t *paging)
     /* Don't page out page 0 */
     set_bit(0, bitmap);
 
-    rc = 0;
-
  out:
     return rc;
 }
@@ -61,17 +71,27 @@ int policy_choose_victim(xc_interface *xch,
                          xenpaging_t *paging, domid_t domain_id,
                          xenpaging_victim_t *victim)
 {
+    unsigned long wrap = current_gfn;
     ASSERT(victim != NULL);
 
     /* Domain to pick on */
     victim->domain_id = domain_id;
-    
+
     do
     {
-        /* Randomly choose a gfn to evict */
-        victim->gfn = rand() % paging->domain_info->max_pages;
+        current_gfn++;
+        if ( current_gfn >= max_pages )
+            current_gfn = 0;
+        if ( wrap == current_gfn )
+        {
+            victim->gfn = INVALID_MFN;
+            return -ENOSPC;
+        }
     }
-    while ( test_bit(victim->gfn, bitmap) );
+    while ( test_bit(current_gfn, bitmap) || test_bit(current_gfn, unconsumed) );
+
+    set_bit(current_gfn, unconsumed);
+    victim->gfn = current_gfn;
 
     return 0;
 }
@@ -79,6 +99,7 @@ int policy_choose_victim(xc_interface *xch,
 void policy_notify_paged_out(domid_t domain_id, unsigned long gfn)
 {
     set_bit(gfn, bitmap);
+    clear_bit(gfn, unconsumed);
 }
 
 void policy_notify_paged_in(domid_t domain_id, unsigned long gfn)

diff --git a/tools/xenpaging/xenpaging.c b/tools/xenpaging/xenpaging.c
index b3b579ef9662860db48a53f95690acffbc002033..778537bd5c473b81fe2c15c776aa97f6b17c2bc0 100644 (file)
--- a/tools/xenpaging/xenpaging.c
+++ b/tools/xenpaging/xenpaging.c
@@ -446,7 +446,8 @@ static int evict_victim(xc_interface *xch, xenpaging_t *paging, domid_t domain_i
         ret = policy_choose_victim(xch, paging, domain_id, victim);
         if ( ret != 0 )
         {
-            ERROR("Error choosing victim");
+            if ( ret != -ENOSPC )
+                ERROR("Error choosing victim");
             goto out;
         }
 
@@ -525,7 +526,9 @@ int main(int argc, char *argv[])
     memset(victims, 0, sizeof(xenpaging_victim_t) * num_pages);
     for ( i = 0; i < num_pages; i++ )
     {
-        evict_victim(xch, paging, domain_id, &victims[i], fd, i);
+        rc = evict_victim(xch, paging, domain_id, &victims[i], fd, i);
+        if ( rc == -ENOSPC )
+            break;
         if ( i % 100 == 0 )
             DPRINTF("%d pages evicted\n", i);
     }