Add a fragmentation fallback in ggc-page v2

There were some concerns that the earlier munmap patch could lead
to address space being freed that cannot be allocated again
by ggc due to fragmentation. This patch adds a fragmentation
fallback to solve this: when a GGC_QUIRE_SIZE sized allocation fails,
try again with a page sized allocation.

Passes bootstrap and testing on x86_64-linux with the fallback
forced artificially.

v2: fix missed initialization bug added in last minute edit.

gcc/:
2011-10-20  Andi Kleen  <ak@linux.intel.com>

	* ggc-page (alloc_anon): Add check argument.
	(alloc_page): Add fallback to 1 page allocation.
	Adjust alloc_anon calls to new argument.

From-SVN: r180649

gcc/ChangeLog

+2011-10-20  Andi Kleen  <ak@linux.intel.com>
+
+	* ggc-page (alloc_anon): Add check argument.
+	(alloc_page): Add fallback to 1 page allocation.
+	Adjust alloc_anon calls to new argument.
+
 2011-10-18  Andi Kleen  <ak@linux.intel.com>
 
 	* ggc-page (release_pages): First free large continuous

gcc/ggc-page.c

@@ -483,7 +483,7 @@ static int ggc_allocated_p (const void *);
 static page_entry *lookup_page_table_entry (const void *);
 static void set_page_table_entry (void *, page_entry *);
 #ifdef USING_MMAP
-static char *alloc_anon (char *, size_t);
+static char *alloc_anon (char *, size_t, bool check);
 #endif
 #ifdef USING_MALLOC_PAGE_GROUPS
 static size_t page_group_index (char *, char *);
@@ -662,7 +662,7 @@ debug_print_page_list (int order)
    compile error unless exactly one of the HAVE_* is defined.  */
 
 static inline char *
-alloc_anon (char *pref ATTRIBUTE_UNUSED, size_t size)
+alloc_anon (char *pref ATTRIBUTE_UNUSED, size_t size, bool check)
 {
 #ifdef HAVE_MMAP_ANON
   char *page = (char *) mmap (pref, size, PROT_READ | PROT_WRITE,
@@ -675,6 +675,8 @@ alloc_anon (char *pref ATTRIBUTE_UNUSED, size_t size)
 
   if (page == (char *) MAP_FAILED)
     {
+      if (!check)
+        return NULL;
       perror ("virtual memory exhausted");
       exit (FATAL_EXIT_CODE);
     }
@@ -777,13 +779,18 @@ alloc_page (unsigned order)
 	 extras on the freelist.  (Can only do this optimization with
 	 mmap for backing store.)  */
       struct page_entry *e, *f = G.free_pages;
-      int i;
+      int i, entries = GGC_QUIRE_SIZE;
 
-      page = alloc_anon (NULL, G.pagesize * GGC_QUIRE_SIZE);
+      page = alloc_anon (NULL, G.pagesize * GGC_QUIRE_SIZE, false);
+      if (page == NULL)
+     	{
+	  page = alloc_anon(NULL, G.pagesize, true);
+          entries = 1;
+	}
 
       /* This loop counts down so that the chain will be in ascending
 	 memory order.  */
-      for (i = GGC_QUIRE_SIZE - 1; i >= 1; i--)
+      for (i = entries - 1; i >= 1; i--)
 	{
 	  e = XCNEWVAR (struct page_entry, page_entry_size);
 	  e->order = order;
@@ -796,7 +803,7 @@ alloc_page (unsigned order)
       G.free_pages = f;
     }
   else
-    page = alloc_anon (NULL, entry_size);
+    page = alloc_anon (NULL, entry_size, true);
 #endif
 #ifdef USING_MALLOC_PAGE_GROUPS
   else
@@ -1649,14 +1656,14 @@ init_ggc (void)
      believe, is an unaligned page allocation, which would cause us to
      hork badly if we tried to use it.  */
   {
-    char *p = alloc_anon (NULL, G.pagesize);
+    char *p = alloc_anon (NULL, G.pagesize, true);
     struct page_entry *e;
     if ((size_t)p & (G.pagesize - 1))
       {
 	/* How losing.  Discard this one and try another.  If we still
 	   can't get something useful, give up.  */
 
-	p = alloc_anon (NULL, G.pagesize);
+	p = alloc_anon (NULL, G.pagesize, true);
 	gcc_assert (!((size_t)p & (G.pagesize - 1)));
       }