[PATCH -v7 1/2] Massive code cleanup of sys_msync()

[Anton Salikhmetov]

Use the PAGE_ALIGN() macro instead of "manual" alignment.
Improve readability of the loop, which traverses the process
memory regions. Make code more symmetric and possibly boost
performance on some RISC CPUs by moving variable assignments.

Signed-off-by: Anton Salikhmetov <salikhmetov@xxxxxxxxx>
---
 mm/msync.c |   77 ++++++++++++++++++++++++++++--------------------------------
 1 files changed, 36 insertions(+), 41 deletions(-)

diff --git a/mm/msync.c b/mm/msync.c
index 144a757..a4de868 100644
--- a/mm/msync.c
+++ b/mm/msync.c
@@ -1,85 +1,83 @@
 /*
- *	linux/mm/msync.c
+ * The msync() system call.
  *
- * Copyright (C) 1994-1999  Linus Torvalds
+ * Copyright (C) 1994-1999 Linus Torvalds
+ * Copyright (C) 2008 Anton Salikhmetov <salikhmetov@xxxxxxxxx>
  */
 
-/*
- * The msync() system call.
- */
+#include <linux/file.h>
 #include <linux/fs.h>
 #include <linux/mm.h>
 #include <linux/mman.h>
-#include <linux/file.h>
-#include <linux/syscalls.h>
 #include <linux/sched.h>
+#include <linux/syscalls.h>
 
 /*
  * MS_SYNC syncs the entire file - including mappings.
  *
  * MS_ASYNC does not start I/O (it used to, up to 2.5.67).
- * Nor does it marks the relevant pages dirty (it used to up to 2.6.17).
+ * Nor does it mark the relevant pages dirty (it used to up to 2.6.17).
  * Now it doesn't do anything, since dirty pages are properly tracked.
  *
- * The application may now run fsync() to
- * write out the dirty pages and wait on the writeout and check the result.
- * Or the application may run fadvise(FADV_DONTNEED) against the fd to start
- * async writeout immediately.
+ * The application may now run fsync() to write out the dirty pages and
+ * wait on the writeout and check the result. Or the application may run
+ * fadvise(FADV_DONTNEED) against the fd to start async writeout immediately.
  * So by _not_ starting I/O in MS_ASYNC we provide complete flexibility to
  * applications.
  */
 asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
 {
 	unsigned long end;
-	struct mm_struct *mm = current->mm;
+	int error, unmapped_error;
 	struct vm_area_struct *vma;
-	int unmapped_error = 0;
-	int error = -EINVAL;
+	struct mm_struct *mm;
 
+	error = -EINVAL;
 	if (flags & ~(MS_ASYNC | MS_INVALIDATE | MS_SYNC))
 		goto out;
 	if (start & ~PAGE_MASK)
 		goto out;
 	if ((flags & MS_ASYNC) && (flags & MS_SYNC))
 		goto out;
+
 	error = -ENOMEM;
-	len = (len + ~PAGE_MASK) & PAGE_MASK;
+	len = PAGE_ALIGN(len);
 	end = start + len;
 	if (end < start)
 		goto out;
-	error = 0;
+
+	error = unmapped_error = 0;
 	if (end == start)
 		goto out;
+
 	/*
 	 * If the interval [start,end) covers some unmapped address ranges,
 	 * just ignore them, but return -ENOMEM at the end.
 	 */
+	mm = current->mm;
 	down_read(&mm->mmap_sem);
 	vma = find_vma(mm, start);
-	for (;;) {
+	do {
 		struct file *file;
 
-		/* Still start < end. */
 		error = -ENOMEM;
 		if (!vma)
-			goto out_unlock;
-		/* Here start < vma->vm_end. */
+			break;
 		if (start < vma->vm_start) {
 			start = vma->vm_start;
 			if (start >= end)
-				goto out_unlock;
-			unmapped_error = -ENOMEM;
-		}
-		/* Here vma->vm_start <= start < vma->vm_end. */
-		if ((flags & MS_INVALIDATE) &&
-				(vma->vm_flags & VM_LOCKED)) {
-			error = -EBUSY;
-			goto out_unlock;
+				break;
+			unmapped_error = error;
 		}
-		file = vma->vm_file;
+
+		error = -EBUSY;
+		if ((flags & MS_INVALIDATE) && (vma->vm_flags & VM_LOCKED))
+			break;
+
+		error = 0;
 		start = vma->vm_end;
-		if ((flags & MS_SYNC) && file &&
-				(vma->vm_flags & VM_SHARED)) {
+		file = vma->vm_file;
+		if (file && (vma->vm_flags & VM_SHARED) && (flags & MS_SYNC)) {
 			get_file(file);
 			up_read(&mm->mmap_sem);
 			error = do_fsync(file, 0);
@@ -88,16 +86,13 @@ asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
 				goto out;
 			down_read(&mm->mmap_sem);
 			vma = find_vma(mm, start);
-		} else {
-			if (start >= end) {
-				error = 0;
-				goto out_unlock;
-			}
-			vma = vma->vm_next;
+			continue;
 		}
-	}
-out_unlock:
+
+		vma = vma->vm_next;
+	} while (start < end);
 	up_read(&mm->mmap_sem);
+
 out:
-	return error ? : unmapped_error;
+	return error ? error : unmapped_error;
 }
-- 
1.4.4.4

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