Subject: xenpaging: specify policy mru_size at runtime

The environment variable XENPAGING_POLICY_MRU_SIZE will change the mru_size in
the policy at runtime.
Specifying the mru_size at runtime allows the admin to keep more pages in
memory so guests can make more progress.  Its also good for development to
reduce the value to put more pressure on the paging related code paths.

(xen-unstable changeset:   22700:f87b1c194eb8)

Signed-off-by: Olaf Hering <olaf@aepfle.de>

---
 tools/xenpaging/policy_default.c |   21 +++++++++++++++++----
 tools/xenpaging/xenpaging.c      |    8 ++++++++
 tools/xenpaging/xenpaging.h      |    1 +
 3 files changed, 26 insertions(+), 4 deletions(-)

Index: xen-4.0.2-testing/tools/xenpaging/policy_default.c
===================================================================
--- xen-4.0.2-testing.orig/tools/xenpaging/policy_default.c
+++ xen-4.0.2-testing/tools/xenpaging/policy_default.c
@@ -29,7 +29,8 @@
 #define MRU_SIZE (1024 * 16)
 
 
-static unsigned long mru[MRU_SIZE];
+static unsigned long *mru;
+static unsigned int mru_size;
 static unsigned int i_mru;
 static unsigned long *bitmap;
 static unsigned long *unconsumed;
@@ -56,8 +57,20 @@ int policy_init(xenpaging_t *paging)
     bitmap_size = paging->bitmap_size;
     max_pages = paging->domain_info->max_pages;
 
+    if ( paging->policy_mru_size > 0 )
+        mru_size = paging->policy_mru_size;
+    else
+        mru_size = MRU_SIZE;
+
+    mru = malloc(sizeof(*mru) * mru_size);
+    if ( mru == NULL )
+    {
+        rc = -ENOMEM;
+        goto out;
+    }
+
     /* Initialise MRU list of paged in pages */
-    for ( i = 0; i < MRU_SIZE; i++ )
+    for ( i = 0; i < mru_size; i++ )
         mru[i] = INVALID_MFN;
 
     /* Don't page out first 16MB */
@@ -100,12 +113,12 @@ void policy_notify_paged_out(unsigned lo
 
 void policy_notify_paged_in(unsigned long gfn)
 {
-    unsigned long old_gfn = mru[i_mru & (MRU_SIZE - 1)];
+    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;
+    mru[i_mru & (mru_size - 1)] = gfn;
     i_mru++;
 }
 
Index: xen-4.0.2-testing/tools/xenpaging/xenpaging.c
===================================================================
--- xen-4.0.2-testing.orig/tools/xenpaging/xenpaging.c
+++ xen-4.0.2-testing/tools/xenpaging/xenpaging.c
@@ -80,6 +80,7 @@ static void *init_page(void)
 xenpaging_t *xenpaging_init(domid_t domain_id)
 {
     xenpaging_t *paging;
+    char *p;
     int rc;
 
     DPRINTF("xenpaging init\n");
@@ -96,6 +97,13 @@ xenpaging_t *xenpaging_init(domid_t doma
         goto err;
     }
 
+    p = getenv("XENPAGING_POLICY_MRU_SIZE");
+    if ( p && *p )
+    {
+        paging->policy_mru_size = atoi(p);
+        DPRINTF("Setting policy mru_size to %d\n", paging->policy_mru_size);
+    }
+
     /* Set domain id */
     paging->mem_event.domain_id = domain_id;
 
Index: xen-4.0.2-testing/tools/xenpaging/xenpaging.h
===================================================================
--- xen-4.0.2-testing.orig/tools/xenpaging/xenpaging.h
+++ xen-4.0.2-testing/tools/xenpaging/xenpaging.h
@@ -37,6 +37,7 @@
 
 typedef struct xenpaging {
     int xc_handle;
+    int policy_mru_size;
 
     xc_platform_info_t *platform_info;
     xc_domaininfo_t    *domain_info;