[PATCH] ia64: support arch_get_unmapped_area() cache

Add support for the mm->free_area_cache so that we do not stupidly
search from TASK_UNMAPPED_BASE every time we need to allocate some
virtual memory.

arch/ia64/kernel/sys_ia64.c

@@ -26,8 +26,9 @@ arch_get_unmapped_area (struct file *filp, unsigned long addr, unsigned long len
 			unsigned long pgoff, unsigned long flags)
 {
 	long map_shared = (flags & MAP_SHARED);
-	unsigned long align_mask = PAGE_SIZE - 1;
-	struct vm_area_struct * vmm;
+	unsigned long start_addr, align_mask = PAGE_SIZE - 1;
+	struct mm_struct *mm = current->mm;
+	struct vm_area_struct *vma;
 
 	if (len > RGN_MAP_LIMIT)
 		return -ENOMEM;
@@ -37,7 +38,7 @@ arch_get_unmapped_area (struct file *filp, unsigned long addr, unsigned long len
 		addr = 0;
 #endif
 	if (!addr)
-		addr = TASK_UNMAPPED_BASE;
+		addr = mm->free_area_cache;
 
 	if (map_shared && (TASK_SIZE > 0xfffffffful))
 		/*
@@ -48,17 +49,25 @@ arch_get_unmapped_area (struct file *filp, unsigned long addr, unsigned long len
 		 */
 		align_mask = SHMLBA - 1;
 
-	addr = (addr + align_mask) & ~align_mask;
-
-	for (vmm = find_vma(current->mm, addr); ; vmm = vmm->vm_next) {
-		/* At this point:  (!vmm || addr < vmm->vm_end). */
-		if (TASK_SIZE - len < addr)
-			return -ENOMEM;
-		if (REGION_OFFSET(addr) + len > RGN_MAP_LIMIT)	/* no risk of overflow here... */
+  full_search:
+	start_addr = addr = (addr + align_mask) & ~align_mask;
+
+	for (vma = find_vma(mm, addr); ; vma = vma->vm_next) {
+		/* At this point:  (!vma || addr < vma->vm_end). */
+		if (TASK_SIZE - len < addr || RGN_MAP_LIMIT - len < REGION_OFFSET(addr)) {
+			if (start_addr != TASK_UNMAPPED_BASE) {
+				/* Start a new search --- just in case we missed some holes.  */
+				addr = TASK_UNMAPPED_BASE;
+				goto full_search;
+			}
 			return -ENOMEM;
-		if (!vmm || addr + len <= vmm->vm_start)
+		}
+		if (!vma || addr + len <= vma->vm_start) {
+			/* Remember the address where we stopped this search:  */
+			mm->free_area_cache = addr + len;
 			return addr;
-		addr = (vmm->vm_end + align_mask) & ~align_mask;
+		}
+		addr = (vma->vm_end + align_mask) & ~align_mask;
 	}
 }