[Xen-changelog] [xen-unstable] xenpaging: break endless loop during inital page-out with large pagefiles

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

# HG changeset patch
# User Keir Fraser <keir@xxxxxxx>
# Date 1290780921 0
# Node ID 0d0a18cd416f55921a686c32a1a8955d80907545
# Parent  66df4f35b8deef7d23087c275dc517ce8412446e
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@xxxxxxxxx>
Already-Acked-by: Patrick Colp <pjcolp@xxxxxxxxx>
Already-Acked-by: Keir Fraser <keir.fraser@xxxxxxxxxx>
---
 tools/xenpaging/policy_default.c |   35 ++++++++++++++++++++++++++++-------
 tools/xenpaging/xenpaging.c      |    7 +++++--
 2 files changed, 33 insertions(+), 9 deletions(-)

diff -r 66df4f35b8de -r 0d0a18cd416f tools/xenpaging/policy_default.c
--- a/tools/xenpaging/policy_default.c  Fri Nov 26 10:10:40 2010 +0000
+++ b/tools/xenpaging/policy_default.c  Fri Nov 26 14:15:21 2010 +0000
@@ -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)
@@ -43,6 +47,14 @@ int policy_init(xenpaging_t *paging)
     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++ )
@@ -50,8 +62,6 @@ 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 *x
                          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 @@ void policy_notify_paged_out(domid_t dom
 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 -r 66df4f35b8de -r 0d0a18cd416f tools/xenpaging/xenpaging.c
--- a/tools/xenpaging/xenpaging.c       Fri Nov 26 10:10:40 2010 +0000
+++ b/tools/xenpaging/xenpaging.c       Fri Nov 26 14:15:21 2010 +0000
@@ -446,7 +446,8 @@ static int evict_victim(xc_interface *xc
         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);
     }

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