[PATCH 2/3] malloc: Only fill half of the tcache during batch allocation

[Florian Weimer]

This leaves room for subsequent frees.
---
 malloc/malloc.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/malloc/malloc.c b/malloc/malloc.c
index d2184c8d7a..d42f0183e3 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -3940,8 +3940,11 @@ _int_malloc (mstate av, size_t bytes)
 	      if (__glibc_unlikely (tcache_inactive ()))
 		tcache_init (av);
 
-	      /* While bin not empty and tcache not full, copy chunks over.  */
-	      while (tcache->num_slots[tc_idx] != 0
+	      /* While bin not empty and tcache not full, copy chunks over.
+		 Only fill half of the tcache, so that subsequent frees
+		 do not immediately flush the tcache.  */
+	      unsigned int tcache_target_count = mp_.tcache_count / 2;
+	      while (tcache->num_slots[tc_idx] > tcache_target_count
 		     && (tc_victim = last (bin)) != bin)
 		{
 		  if (tc_victim != NULL)
@@ -3988,6 +3991,7 @@ _int_malloc (mstate av, size_t bytes)
   if (tc_idx < mp_.tcache_small_bins)
     tcache_nb = nb;
   int return_cached = 0;
+  unsigned int tcache_target_count = mp_.tcache_count / 2;
 
   tcache_unsorted_count = 0;
 #endif
@@ -4066,9 +4070,11 @@ _int_malloc (mstate av, size_t bytes)
 	      if (__glibc_unlikely (tcache_inactive ()))
 		tcache_init (av);
 	      /* Fill cache first, return to user only if cache fills.
-		 We may return one of these chunks later.  */
+		 We may return one of these chunks later.  Only fill
+		 half of tcache, so that subsequent frees do not flush
+		 it immediately.  */
 	      if (tcache_nb > 0
-		  && tcache->num_slots[tc_idx] != 0)
+		  && tcache->num_slots[tc_idx] > tcache_target_count)
 		{
 		  tcache_put (victim, tc_idx);
 		  return_cached = 1;
-- 
2.52.0