mm: don't hold heap lock in alloc_heap_pages() longer than necessary

Once pages are removed from the heap we don't need to hold the heap
lock. It is especially useful to drop it for an unscrubbed buddy since
we will be scrubbing it.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>

diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 9fa62d26bacce136f00f452dd72408c8df9ba81d..12e06fd71c69699a5e7845ac2d09cedce3526688 100644 (file)
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -855,6 +855,7 @@ static struct page_info *alloc_heap_pages(
     struct page_info *pg;
     bool need_tlbflush = false;
     uint32_t tlbflush_timestamp = 0;
+    unsigned int dirty_cnt = 0;
 
     /* Make sure there are enough bits in memflags for nodeID. */
     BUILD_BUG_ON((_MEMF_bits - _MEMF_node) < (8 * sizeof(nodeid_t)));
@@ -943,6 +944,8 @@ static struct page_info *alloc_heap_pages(
     if ( d != NULL )
         d->last_alloc_node = node;
 
+    spin_unlock(&heap_lock);
+
     for ( i = 0; i < (1 << order); i++ )
     {
         /* Reference count must continuously be zero for free pages. */
@@ -952,7 +955,7 @@ static struct page_info *alloc_heap_pages(
         {
             if ( !(memflags & MEMF_no_scrub) )
                 scrub_one_page(&pg[i]);
-            node_need_scrub[node]--;
+            dirty_cnt++;
         }
 
         pg[i].count_info = PGC_state_inuse;
@@ -974,6 +977,8 @@ static struct page_info *alloc_heap_pages(
             check_one_page(&pg[i]);
     }
 
+    spin_lock(&heap_lock);
+    node_need_scrub[node] -= dirty_cnt;
     spin_unlock(&heap_lock);
 
     if ( need_tlbflush )