[PATCH v2][BZ #11087] Use atomic operations to track memory

[OndÅej BÃlka <neleai at seznam dot cz>]

On Thu, Oct 17, 2013 at 01:41:40PM +0200, OndÅej BÃlka wrote:
> Hi,
> 
> I fixed this mostly because ulrich was wrong here in several ways. 
> 
> Calling added locking to update statistics as too expensive is nonsense
> as this is needed only after mmap and mmap + associated minor faults
> are much more costy.
> 
> Also there is no locking needed, atomic add will do job well.
> 
> This bug affects also malloc_stats.
> 
> Comments?
> 

Here is version that uses atomic* functions and tracks accurately
maximum. OK to commit?

	[BZ #11087]
	* malloc/malloc.c: Accurately track mmaped memory.

diff --git a/malloc/malloc.c b/malloc/malloc.c
index 1a18c3f..b814062 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -2325,12 +2325,11 @@ static void* sysmalloc(INTERNAL_SIZE_T nb, mstate av)
 
 	/* update statistics */
 
-	if (++mp_.n_mmaps > mp_.max_n_mmaps)
-	  mp_.max_n_mmaps = mp_.n_mmaps;
+	int old = atomic_exchange_and_add (&mp_.n_mmaps, 1);
+	atomic_max (&mp_.max_n_mmaps, old + 1);
 
-	sum = mp_.mmapped_mem += size;
-	if (sum > (unsigned long)(mp_.max_mmapped_mem))
-	  mp_.max_mmapped_mem = sum;
+	sum = atomic_exchange_and_add(&mp_.mmapped_mem, size) + size;
+	atomic_max (&mp_.max_mmapped_mem, sum);
 
 	check_chunk(av, p);
 
@@ -2780,8 +2779,8 @@ munmap_chunk(mchunkptr p)
       return;
     }
 
-  mp_.n_mmaps--;
-  mp_.mmapped_mem -= total_size;
+  atomic_decrement (&mp_.n_mmaps);
+  atomic_add (&mp_.mmapped_mem, -total_size);
 
   /* If munmap failed the process virtual memory address space is in a
      bad shape.  Just leave the block hanging around, the process will
@@ -2798,6 +2797,7 @@ mremap_chunk(mchunkptr p, size_t new_size)
   size_t page_mask = GLRO(dl_pagesize) - 1;
   INTERNAL_SIZE_T offset = p->prev_size;
   INTERNAL_SIZE_T size = chunksize(p);
+  INTERNAL_SIZE_T old;
   char *cp;
 
   assert (chunk_is_mmapped(p));
@@ -2822,10 +2822,8 @@ mremap_chunk(mchunkptr p, size_t new_size)
   assert((p->prev_size == offset));
   set_head(p, (new_size - offset)|IS_MMAPPED);
 
-  mp_.mmapped_mem -= size + offset;
-  mp_.mmapped_mem += new_size;
-  if ((unsigned long)mp_.mmapped_mem > (unsigned long)mp_.max_mmapped_mem)
-    mp_.max_mmapped_mem = mp_.mmapped_mem;
+  old = atomic_exchange_and_add (&mp_.mmapped_mem, new_size - size - offset);
+  atomic_max (&mp_.max_mmapped_mem, old + new_size - size - offset);
   return p;
 }