1 files changed, 47 insertions, 1 deletions

diff --git a/gcc/ggc-page.c b/gcc/ggc-page.c
index beee851..9b35291 100644
--- a/gcc/ggc-page.c
+++ b/gcc/ggc-page.c
@@ -50,6 +50,10 @@ along with GCC; see the file COPYING3.  If not see
 #define USING_MALLOC_PAGE_GROUPS
 #endif
 
+#if defined(HAVE_MADVISE) && defined(MADV_DONTNEED)
+# define USING_MADVISE
+#endif
+
 /* Strategy:
 
    This garbage-collecting allocator allocates objects on one of a set
@@ -277,6 +281,9 @@ typedef struct page_entry
   /* The lg of size of objects allocated from this page.  */
   unsigned char order;
 
+  /* Discarded page? */
+  bool discarded;
+
   /* A bit vector indicating whether or not objects are in use.  The
      Nth bit is one if the Nth object on this page is allocated.  This
      array is dynamically sized.  */
@@ -740,6 +747,10 @@ alloc_page (unsigned order)
 
   if (p != NULL)
     {
+      if (p->discarded)
+        G.bytes_mapped += p->bytes;
+      p->discarded = false;
+
       /* Recycle the allocated memory from this page ...  */
       *pp = p->next;
       page = p->page;
@@ -956,7 +967,42 @@ free_page (page_entry *entry)
 static void
 release_pages (void)
 {
-#ifdef USING_MMAP
+#ifdef USING_MADVISE
+  page_entry *p, *start_p;
+  char *start;
+  size_t len;
+
+  for (p = G.free_pages; p; )
+    {
+      if (p->discarded)
+        {
+          p = p->next;
+          continue;
+        }
+      start = p->page;
+      len = p->bytes;
+      start_p = p;
+      p = p->next;
+      while (p && p->page == start + len)
+        {
+          len += p->bytes;
+          p = p->next;
+        }
+      /* Give the page back to the kernel, but don't free the mapping.
+         This avoids fragmentation in the virtual memory map of the 
+ 	 process. Next time we can reuse it by just touching it. */
+      madvise (start, len, MADV_DONTNEED);
+      /* Don't count those pages as mapped to not touch the garbage collector
+         unnecessarily. */
+      G.bytes_mapped -= len;
+      while (start_p != p)
+        {
+          start_p->discarded = true;
+          start_p = start_p->next;
+        }
+    }
+#endif
+#if defined(USING_MMAP) && !defined(USING_MADVISE)
   page_entry *p, *next;
   char *start;
   size_t len;