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authorWilco Dijkstra <wdijkstr@arm.com>2017-10-20 17:27:53 +0100
committerWilco Dijkstra <wdijkstr@arm.com>2017-10-20 17:31:06 +0100
commita15d53e2de4c7d83bda251469d92a3c7b49a90db (patch)
tree6ed955b98d9166a0c9d85c30d1898a4d9238a3e9 /malloc
parentb9a558e790c7f13f04f3fcf229f12543b8119732 (diff)
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Add single-threaded path to _int_free
This patch adds single-threaded fast paths to _int_free.
Bypass the explicit locking for larger allocations.

	* malloc/malloc.c (_int_free): Add SINGLE_THREAD_P fast paths.
Diffstat (limited to 'malloc')
-rw-r--r--malloc/malloc.c43
1 files changed, 29 insertions, 14 deletions
diff --git a/malloc/malloc.c b/malloc/malloc.c
index 3d7c23917c..4db21cc8c1 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -4159,24 +4159,34 @@ _int_free (mstate av, mchunkptr p, int have_lock)
 
     /* Atomically link P to its fastbin: P->FD = *FB; *FB = P;  */
     mchunkptr old = *fb, old2;
-    unsigned int old_idx = ~0u;
-    do
+
+    if (SINGLE_THREAD_P)
       {
-	/* Check that the top of the bin is not the record we are going to add
-	   (i.e., double free).  */
+	/* Check that the top of the bin is not the record we are going to
+	   add (i.e., double free).  */
 	if (__builtin_expect (old == p, 0))
 	  malloc_printerr ("double free or corruption (fasttop)");
-	/* Check that size of fastbin chunk at the top is the same as
-	   size of the chunk that we are adding.  We can dereference OLD
-	   only if we have the lock, otherwise it might have already been
-	   deallocated.  See use of OLD_IDX below for the actual check.  */
-	if (have_lock && old != NULL)
-	  old_idx = fastbin_index(chunksize(old));
-	p->fd = old2 = old;
+	p->fd = old;
+	*fb = p;
       }
-    while ((old = catomic_compare_and_exchange_val_rel (fb, p, old2)) != old2);
-
-    if (have_lock && old != NULL && __builtin_expect (old_idx != idx, 0))
+    else
+      do
+	{
+	  /* Check that the top of the bin is not the record we are going to
+	     add (i.e., double free).  */
+	  if (__builtin_expect (old == p, 0))
+	    malloc_printerr ("double free or corruption (fasttop)");
+	  p->fd = old2 = old;
+	}
+      while ((old = catomic_compare_and_exchange_val_rel (fb, p, old2))
+	     != old2);
+
+    /* Check that size of fastbin chunk at the top is the same as
+       size of the chunk that we are adding.  We can dereference OLD
+       only if we have the lock, otherwise it might have already been
+       allocated again.  */
+    if (have_lock && old != NULL
+	&& __builtin_expect (fastbin_index (chunksize (old)) != idx, 0))
       malloc_printerr ("invalid fastbin entry (free)");
   }
 
@@ -4185,6 +4195,11 @@ _int_free (mstate av, mchunkptr p, int have_lock)
   */
 
   else if (!chunk_is_mmapped(p)) {
+
+    /* If we're single-threaded, don't lock the arena.  */
+    if (SINGLE_THREAD_P)
+      have_lock = true;
+
     if (!have_lock)
       __libc_lock_lock (av->mutex);