Xen devel - Nov 2011 - [PATCH] xenpaging: improve policy mru list handling

# HG changeset patch
# User Olaf Hering <olaf@aepfle.de>
# Date 1320258644 -3600
# Node ID af9eb3b6c6d874e54d28bec61c32e0c4668d2b47
# Parent  79677f532a2406ca501250b50fa8b33965a8d7d7
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>

diff -r 79677f532a24 -r af9eb3b6c6d8 tools/xenpaging/policy.h
--- 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 -r 79677f532a24 -r af9eb3b6c6d8 tools/xenpaging/policy_default.c
--- 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 lo
     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 -r 79677f532a24 -r af9eb3b6c6d8 tools/xenpaging/xenpaging.c
--- a/tools/xenpaging/xenpaging.c
+++ b/tools/xenpaging/xenpaging.c
@@ -618,7 +618,14 @@ static int xenpaging_resume_page(xenpagi
     /* 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--;
@@ -889,7 +896,7 @@ 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
                 {

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Olaf Hering writes ("[Xen-devel] [PATCH] xenpaging: improve policy mru list
handling"):
> xenpaging: improve policy mru list handling
This does not apply to xen-unstable tip, I''m afraid.

Ian.

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