[PATCH] release all idle heaps in the non-main-arena

[liudongyun]

liu.dongyun@h3c.com report this question in follow:
The system has a total of 32G memory and 12 core cpu. 
After frequent malloc and free memory by multiple threads, we found that many
physical memory that should have been released have not been released.We observe that 
the maximum free memory can reach 15G.

deng.hongjie@h3c.com recommend reducing the heap size of the non-main-arena, but it 
doesn't work. liu.dongyun@h3c.com found When the last heap in the user process into 
the non-main-area has memory in use, the previous heap will not be released, even if the 
previous heap is already free. This mechanism resulting in the memory cache reaching 15G.

liu.dongyun@h3c.com tried to solve this problem by checking to release the heap that the 
current chunk belongs to and unmmaped if it is all free. Then we adjust the heap size of
the non-main-arena to 512KB. The method has achieved good results. Submit patch only to 
modify one of them.

The test after modification has the following results. 

With business:
--------------------------------------------------------------------------------
Memory statistics are measured in KB:                                           
Slot 0:                                                                         
             Total      Used      Free    Shared   Buffers    Cached   FreeRatio
Mem:      32598612   7501484  25097128         0      1812   2121380       77.0%
--------------------------------------------------------------------------------

A few minutes after deleted business:
Memory statistics are measured in KB:                                           
Slot 0:                                                                         
             Total      Used      Free    Shared   Buffers    Cached   FreeRatio
Mem:      32598612   9763528  22835084         0        32   2118208       70.0%
--------------------------------------------------------------------------------

Bugzilla: https://sourceware.org/bugzilla/show_bug.cgi?id=27976
Reported-by: liudongyun <liu.dongyun@h3c.com> and
Reported-by: denghongjie <deng.hongjie@h3c.com>


---
 malloc/arena.c  | 30 +++++++++++++++++++++++++++++-
 malloc/malloc.c |  2 +-
 2 files changed, 30 insertions(+), 2 deletions(-)
 mode change 100644 => 100755 malloc/arena.c
 mode change 100644 => 100755 malloc/malloc.c

diff --git a/malloc/arena.c b/malloc/arena.c
old mode 100644
new mode 100755
index 7eb110445e..7812997886
--- a/malloc/arena.c
+++ b/malloc/arena.c
@@ -606,14 +606,42 @@ shrink_heap (heap_info *h, long diff)
     } while (0)
 
 static int
-heap_trim (heap_info *heap, size_t pad)
+heap_trim(heap_info *heap, heap_info *free_heap, size_t pad)
 {
   mstate ar_ptr = heap->ar_ptr;
   unsigned long pagesz = GLRO (dl_pagesize);
   mchunkptr top_chunk = top (ar_ptr), p;
   heap_info *prev_heap;
   long new_size, top_size, top_area, extra, prev_size, misalign;
+  heap_info *last_heap;
 
+  /*release part of the cache memory*/
+  last_heap = heap_for_ptr(top_chunk);  
+  if ((NULL != free_heap->prev) && (last_heap != free_heap))
+  {
+      p = chunk_at_offset(free_heap, sizeof(*heap));
+      if (!inuse(p))
+      {
+          if (chunksize(p) + sizeof(*free_heap) + MINSIZE == free_heap->size)
+          {
+              while(last_heap)
+              {
+                 if (last_heap->prev == free_heap)
+                 {
+                     last_heap->prev = free_heap->prev;
+                     break;
+                 }
+                 last_heap = last_heap->prev; 
+              }
+              ar_ptr->system_mem -= free_heap->size;
+              arena_mem -= free_heap->size;
+              unlink_chunk(ar_ptr, p);
+              delete_heap(free_heap);
+              return 1;
+          }
+      }
+  }
+  
   /* Can this heap go away completely? */
   while (top_chunk == chunk_at_offset (heap, sizeof (*heap)))
     {
diff --git a/malloc/malloc.c b/malloc/malloc.c
old mode 100644
new mode 100755
index 0e2e1747e0..40f0a8e458
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -4665,7 +4665,7 @@ _int_free (mstate av, mchunkptr p, int have_lock)
 	heap_info *heap = heap_for_ptr(top(av));
 
 	assert(heap->ar_ptr == av);
-	heap_trim(heap, mp_.top_pad);
+	heap_trim(heap, heap_for_ptr(p), mp_.top_pad);
       }
     }
 
-- 
2.17.1