[Xen-devel] [PATCH 4/4] mm: Don't hold heap lock in alloc_heap_pages() longer than necessary

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

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@xxxxxxxxxx>
---
 xen/common/page_alloc.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index b93dae9..1ec788e 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -858,6 +858,7 @@ 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(
 
     check_low_mem_virq();
 
+    spin_unlock(&heap_lock);
+
     if ( d != NULL )
         d->last_alloc_node = node;
 
@@ -955,7 +958,7 @@ 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;
@@ -977,6 +980,8 @@ 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 )
-- 
1.8.3.1


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