File xenpaging.speedup-page-out.evict_pages.free_slot_stack.patch of Package xen

Scanning the victims array for a free slot is expensive.
Remember the last slots freed during page-in requests and reuse them in evict_victims.
---
 tools/xenpaging/xenpaging.c |   20 ++++++++++++++++++--
 tools/xenpaging/xenpaging.h |    2 ++
 2 files changed, 20 insertions(+), 2 deletions(-)

Index: xen-4.1.2-testing/tools/xenpaging/xenpaging.c
===================================================================
--- xen-4.1.2-testing.orig/tools/xenpaging/xenpaging.c
+++ xen-4.1.2-testing/tools/xenpaging/xenpaging.c
@@ -787,11 +787,23 @@ static int evict_victim(xenpaging_t *pag
 }
 
 /* Evict a batch of pages and write them to a free slot in the paging file */
-static int evict_pages(xenpaging_t *paging, int fd, xenpaging_victim_t *victims, int num_pages)
+static void evict_pages(xenpaging_t *paging, int fd, xenpaging_victim_t *victims, int num_pages)
 {
     xc_interface *xch = paging->xc_handle;
     int rc, slot, num = 0;
 
+    while ( paging->stack_count > 0 && num < num_pages )
+    {
+        paging->stack_count--;
+        slot = paging->free_slot_stack[paging->stack_count];
+        rc = evict_victim(paging, &victims[slot], fd, slot);
+        if ( rc == -ENOSPC )
+            return;
+        if ( rc == -EINTR )
+            return;
+        num++;
+    }
+
     for ( slot = 0; slot < paging->max_pages && num < num_pages; slot++ )
     {
         /* Slot is allocated */
@@ -807,7 +819,6 @@ static int evict_pages(xenpaging_t *pagi
             DPRINTF("%d pages evicted\n", num);
         num++;
     }
-    return num;
 }
 
 int main(int argc, char *argv[])
@@ -939,6 +950,11 @@ int main(int argc, char *argv[])
 
                 /* Clear this pagefile slot */
                 victims[i].gfn = INVALID_MFN;
+                if ( paging->stack_count < XENPAGING_PAGEIN_QUEUE_SIZE )
+                {
+                    paging->free_slot_stack[paging->stack_count] = i;
+                    paging->stack_count++;
+                }
             }
             else
             {
Index: xen-4.1.2-testing/tools/xenpaging/xenpaging.h
===================================================================
--- xen-4.1.2-testing.orig/tools/xenpaging/xenpaging.h
+++ xen-4.1.2-testing/tools/xenpaging/xenpaging.h
@@ -56,6 +56,8 @@ typedef struct xenpaging {
     int policy_mru_size;
     int use_poll_timeout;
     int debug;
+    int stack_count;
+    int free_slot_stack[XENPAGING_PAGEIN_QUEUE_SIZE];
     unsigned long pagein_queue[XENPAGING_PAGEIN_QUEUE_SIZE];
 } xenpaging_t;