[PATCH] flex mmap for s390(x)

Below is a patch from Pete Zaitcev (zaitcev@redhat.com) to also use the
flex mmap infrastructure for s390(x).  The IBM Domino guys *really* seem to
want this.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/s390/mm/Makefile

@@ -2,6 +2,6 @@
 # Makefile for the linux s390-specific parts of the memory manager.
 #
 
-obj-y	 := init.o fault.o ioremap.o extmem.o
+obj-y	 := init.o fault.o ioremap.o extmem.o mmap.o
 obj-$(CONFIG_CMM) += cmm.o
 

arch/s390/mm/mmap.c

+/*
+ *  linux/arch/s390/mm/mmap.c
+ *
+ *  flexible mmap layout support
+ *
+ * Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
+ * All Rights Reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ *
+ * Started by Ingo Molnar <mingo@elte.hu>
+ */
+
+#include <linux/personality.h>
+#include <linux/mm.h>
+
+/*
+ * Top of mmap area (just below the process stack).
+ *
+ * Leave an at least ~128 MB hole.
+ */
+#define MIN_GAP (128*1024*1024)
+#define MAX_GAP (TASK_SIZE/6*5)
+
+static inline unsigned long mmap_base(void)
+{
+	unsigned long gap = current->rlim[RLIMIT_STACK].rlim_cur;
+
+	if (gap < MIN_GAP)
+		gap = MIN_GAP;
+	else if (gap > MAX_GAP)
+		gap = MAX_GAP;
+
+	return TASK_SIZE - (gap & PAGE_MASK);
+}
+
+static inline int mmap_is_legacy(void)
+{
+#ifdef CONFIG_ARCH_S390X
+	/*
+	 * Force standard allocation for 64 bit programs.
+	 */
+	if (!test_thread_flag(TIF_31BIT))
+		return 1;
+#endif
+	return sysctl_legacy_va_layout ||
+	    (current->personality & ADDR_COMPAT_LAYOUT) ||
+	    current->rlim[RLIMIT_STACK].rlim_cur == RLIM_INFINITY;
+}
+
+/*
+ * This function, called very early during the creation of a new
+ * process VM image, sets up which VM layout function to use:
+ */
+void arch_pick_mmap_layout(struct mm_struct *mm)
+{
+	/*
+	 * Fall back to the standard layout if the personality
+	 * bit is set, or if the expected stack growth is unlimited:
+	 */
+	if (mmap_is_legacy()) {
+		mm->mmap_base = TASK_UNMAPPED_BASE;
+		mm->get_unmapped_area = arch_get_unmapped_area;
+		mm->unmap_area = arch_unmap_area;
+	} else {
+		mm->mmap_base = mmap_base();
+		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
+		mm->unmap_area = arch_unmap_area_topdown;
+	}
+}

include/asm-s390/processor.h

@@ -76,6 +76,8 @@ extern struct task_struct *last_task_used_math;
 
 #define MM_VM_SIZE(mm)		DEFAULT_TASK_SIZE
 
+#define HAVE_ARCH_PICK_MMAP_LAYOUT
+
 typedef struct {
         __u32 ar4;
 } mm_segment_t;