xenpaging: improve policy mru list handling

Without this change it is not possible to page-out all guest pages, then
trigger a page-in for all pages, and then page-out everything once
again. All pages in the mru list can not be paged out because they
remain active in the internal bitmap of paged pages.

Use the mru list only if the number of paged-out pages is larger than
the mru list. If the number is smaller, start to clear the mru list. In
case the number of paged-out pages drops to zero the mru list and the
internal bitmap will be empty as well.

Also add a new interface for dropped pages. If a gfn was dropped there
is no need to adjust the mru list because dropping a page is not usage
of a page.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Committed-by: Ian Jackson <ian.jackson.citrix.com>

3 files changed, 35 insertions, 5 deletions

diff --git a/tools/xenpaging/policy.h b/tools/xenpaging/policy.h
index 18a92569ca..458ed27ce5 100644
--- a/tools/xenpaging/policy.h
+++ b/tools/xenpaging/policy.h
@@ -32,6 +32,8 @@ int policy_init(xenpaging_t *paging);
 int policy_choose_victim(xenpaging_t *paging, xenpaging_victim_t *victim);
 void policy_notify_paged_out(unsigned long gfn);
 void policy_notify_paged_in(unsigned long gfn);
+void policy_notify_paged_in_nomru(unsigned long gfn);
+void policy_notify_dropped(unsigned long gfn);
 
 #endif // __XEN_PAGING_POLICY_H__
 
diff --git a/tools/xenpaging/policy_default.c b/tools/xenpaging/policy_default.c
index 0285d0dd8a..e555ed4e59 100644
--- a/tools/xenpaging/policy_default.c
+++ b/tools/xenpaging/policy_default.c
@@ -57,7 +57,7 @@ int policy_init(xenpaging_t *paging)
     if ( paging->policy_mru_size > 0 )
         mru_size = paging->policy_mru_size;
     else
-        mru_size = DEFAULT_MRU_SIZE;
+        mru_size = paging->policy_mru_size = DEFAULT_MRU_SIZE;
 
     mru = malloc(sizeof(*mru) * mru_size);
     if ( mru == NULL )
@@ -120,17 +120,38 @@ void policy_notify_paged_out(unsigned long gfn)
     clear_bit(gfn, unconsumed);
 }
 
-void policy_notify_paged_in(unsigned long gfn)
+static void policy_handle_paged_in(unsigned long gfn, int do_mru)
 {
     unsigned long old_gfn = mru[i_mru & (mru_size - 1)];
 
     if ( old_gfn != INVALID_MFN )
         clear_bit(old_gfn, bitmap);
     
-    mru[i_mru & (mru_size - 1)] = gfn;
+    if (do_mru) {
+        mru[i_mru & (mru_size - 1)] = gfn;
+    } else {
+        clear_bit(gfn, bitmap);
+        mru[i_mru & (mru_size - 1)] = INVALID_MFN;
+    }
+
     i_mru++;
 }
 
+void policy_notify_paged_in(unsigned long gfn)
+{
+    policy_handle_paged_in(gfn, 1);
+}
+
+void policy_notify_paged_in_nomru(unsigned long gfn)
+{
+    policy_handle_paged_in(gfn, 0);
+}
+
+void policy_notify_dropped(unsigned long gfn)
+{
+    clear_bit(gfn, bitmap);
+}
+
 
 /*
  * Local variables:
diff --git a/tools/xenpaging/xenpaging.c b/tools/xenpaging/xenpaging.c
index f6cd05f700..8f9f52d1e0 100644
--- a/tools/xenpaging/xenpaging.c
+++ b/tools/xenpaging/xenpaging.c
@@ -615,7 +615,14 @@ static int xenpaging_resume_page(xenpaging_t *paging, mem_event_response_t *rsp,
     /* Notify policy of page being paged in */
     if ( notify_policy )
     {
-        policy_notify_paged_in(rsp->gfn);
+        /*
+         * Do not add gfn to mru list if the target is lower than mru size.
+         * This allows page-out of these gfns if the target grows again.
+         */
+        if (paging->num_paged_out > paging->policy_mru_size)
+            policy_notify_paged_in(rsp->gfn);
+        else
+            policy_notify_paged_in_nomru(rsp->gfn);
 
        /* Record number of resumed pages */
        paging->num_paged_out--;
@@ -869,7 +876,7 @@ int main(int argc, char *argv[])
                 {
                     DPRINTF("drop_page ^ gfn %"PRIx64" pageslot %d\n", req.gfn, i);
                     /* Notify policy of page being dropped */
-                    policy_notify_paged_in(req.gfn);
+                    policy_notify_dropped(req.gfn);
                 }
                 else
                 {