[PATCH 3/6] mm: msync() cleanup

[Peter Zijlstra]

From: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>

With the tracking of dirty pages properly done now, msync doesn't need to
scan the PTEs anymore to determine the dirty status.

From: Hugh Dickins <hugh@xxxxxxxxxxx>

In looking to do that, I made some other tidyups: can remove several
#includes, and sys_msync loop termination not quite right.

Most of those points are criticisms of the existing sys_msync, not of
your patch.  In particular, the loop termination errors were introduced
in 2.6.17: I did notice this shortly before it came out, but decided I
was more likely to get it wrong myself, and make matters worse if I
tried to rush a last-minute fix in.  And it's not terribly likely
to go wrong, nor disastrous if it does go wrong (may miss reporting
an unmapped area; may also fsync file of a following vma).

Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Signed-off-by: Hugh Dickins <hugh@xxxxxxxxxxx>

 mm/msync.c |  194 +++++++++----------------------------------------------------
 1 file changed, 31 insertions(+), 163 deletions(-)

Index: 2.6-mm/mm/msync.c
===================================================================
--- 2.6-mm.orig/mm/msync.c	2006-06-22 17:59:06.000000000 +0200
+++ 2.6-mm/mm/msync.c	2006-06-23 13:28:09.000000000 +0200
@@ -7,149 +7,33 @@
 /*
  * The msync() system call.
  */
-#include <linux/slab.h>
-#include <linux/pagemap.h>
 #include <linux/fs.h>
 #include <linux/mm.h>
 #include <linux/mman.h>
-#include <linux/hugetlb.h>
-#include <linux/writeback.h>
 #include <linux/file.h>
 #include <linux/syscalls.h>
 
-#include <asm/pgtable.h>
-#include <asm/tlbflush.h>
-
-static unsigned long msync_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
-				unsigned long addr, unsigned long end)
-{
-	pte_t *pte;
-	spinlock_t *ptl;
-	int progress = 0;
-	unsigned long ret = 0;
-
-again:
-	pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
-	do {
-		struct page *page;
-
-		if (progress >= 64) {
-			progress = 0;
-			if (need_resched() || need_lockbreak(ptl))
-				break;
-		}
-		progress++;
-		if (!pte_present(*pte))
-			continue;
-		if (!pte_maybe_dirty(*pte))
-			continue;
-		page = vm_normal_page(vma, addr, *pte);
-		if (!page)
-			continue;
-		if (ptep_clear_flush_dirty(vma, addr, pte) ||
-				page_test_and_clear_dirty(page))
-			ret += set_page_dirty(page);
-		progress += 3;
-	} while (pte++, addr += PAGE_SIZE, addr != end);
-	pte_unmap_unlock(pte - 1, ptl);
-	cond_resched();
-	if (addr != end)
-		goto again;
-	return ret;
-}
-
-static inline unsigned long msync_pmd_range(struct vm_area_struct *vma,
-			pud_t *pud, unsigned long addr, unsigned long end)
-{
-	pmd_t *pmd;
-	unsigned long next;
-	unsigned long ret = 0;
-
-	pmd = pmd_offset(pud, addr);
-	do {
-		next = pmd_addr_end(addr, end);
-		if (pmd_none_or_clear_bad(pmd))
-			continue;
-		ret += msync_pte_range(vma, pmd, addr, next);
-	} while (pmd++, addr = next, addr != end);
-	return ret;
-}
-
-static inline unsigned long msync_pud_range(struct vm_area_struct *vma,
-			pgd_t *pgd, unsigned long addr, unsigned long end)
-{
-	pud_t *pud;
-	unsigned long next;
-	unsigned long ret = 0;
-
-	pud = pud_offset(pgd, addr);
-	do {
-		next = pud_addr_end(addr, end);
-		if (pud_none_or_clear_bad(pud))
-			continue;
-		ret += msync_pmd_range(vma, pud, addr, next);
-	} while (pud++, addr = next, addr != end);
-	return ret;
-}
-
-static unsigned long msync_page_range(struct vm_area_struct *vma,
-				unsigned long addr, unsigned long end)
-{
-	pgd_t *pgd;
-	unsigned long next;
-	unsigned long ret = 0;
-
-	/* For hugepages we can't go walking the page table normally,
-	 * but that's ok, hugetlbfs is memory based, so we don't need
-	 * to do anything more on an msync().
-	 */
-	if (vma->vm_flags & VM_HUGETLB)
-		return 0;
-
-	BUG_ON(addr >= end);
-	pgd = pgd_offset(vma->vm_mm, addr);
-	flush_cache_range(vma, addr, end);
-	do {
-		next = pgd_addr_end(addr, end);
-		if (pgd_none_or_clear_bad(pgd))
-			continue;
-		ret += msync_pud_range(vma, pgd, addr, next);
-	} while (pgd++, addr = next, addr != end);
-	return ret;
-}
-
 /*
  * MS_SYNC syncs the entire file - including mappings.
  *
- * MS_ASYNC does not start I/O (it used to, up to 2.5.67).  Instead, it just
- * marks the relevant pages dirty.  The application may now run fsync() to
+ * 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).
+ * 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.
  * So by _not_ starting I/O in MS_ASYNC we provide complete flexibility to
  * applications.
  */
-static int msync_interval(struct vm_area_struct *vma, unsigned long addr,
-			unsigned long end, int flags,
-			unsigned long *nr_pages_dirtied)
-{
-	struct file *file = vma->vm_file;
-
-	if ((flags & MS_INVALIDATE) && (vma->vm_flags & VM_LOCKED))
-		return -EBUSY;
-
-	if (file && (vma->vm_flags & VM_SHARED))
-		*nr_pages_dirtied = msync_page_range(vma, addr, end);
-	return 0;
-}
-
 asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
 {
 	unsigned long end;
+	struct mm_struct *mm = current->mm;
 	struct vm_area_struct *vma;
 	int unmapped_error = 0;
 	int error = -EINVAL;
-	int done = 0;
 
 	if (flags & ~(MS_ASYNC | MS_INVALIDATE | MS_SYNC))
 		goto out;
@@ -169,64 +53,48 @@ asmlinkage long sys_msync(unsigned long 
 	 * If the interval [start,end) covers some unmapped address ranges,
 	 * just ignore them, but return -ENOMEM at the end.
 	 */
-	down_read(&current->mm->mmap_sem);
-	vma = find_vma(current->mm, start);
-	if (!vma) {
-		error = -ENOMEM;
-		goto out_unlock;
-	}
-	do {
-		unsigned long nr_pages_dirtied = 0;
+	down_read(&mm->mmap_sem);
+	vma = find_vma(mm, start);
+	for (;;) {
 		struct file *file;
 
+		/* Still start < end. */
+		error = -ENOMEM;
+		if (!vma)
+			goto out_unlock;
 		/* Here start < vma->vm_end. */
 		if (start < vma->vm_start) {
-			unmapped_error = -ENOMEM;
 			start = vma->vm_start;
+			if (start >= end)
+				goto out_unlock;
+			unmapped_error = -ENOMEM;
 		}
 		/* Here vma->vm_start <= start < vma->vm_end. */
-		if (end <= vma->vm_end) {
-			if (start < end) {
-				error = msync_interval(vma, start, end, flags,
-							&nr_pages_dirtied);
-				if (error)
-					goto out_unlock;
-			}
-			error = unmapped_error;
-			done = 1;
-		} else {
-			/* Here vma->vm_start <= start < vma->vm_end < end. */
-			error = msync_interval(vma, start, vma->vm_end, flags,
-						&nr_pages_dirtied);
-			if (error)
-				goto out_unlock;
+		if ((flags & MS_INVALIDATE) &&
+				(vma->vm_flags & VM_LOCKED)) {
+			error = -EBUSY;
+			goto out_unlock;
 		}
 		file = vma->vm_file;
 		start = vma->vm_end;
-		if ((flags & MS_ASYNC) && file && nr_pages_dirtied) {
-			get_file(file);
-			up_read(&current->mm->mmap_sem);
-			balance_dirty_pages_ratelimited_nr(file->f_mapping,
-							nr_pages_dirtied);
-			fput(file);
-			down_read(&current->mm->mmap_sem);
-			vma = find_vma(current->mm, start);
-		} else if ((flags & MS_SYNC) && file &&
+		if ((flags & MS_SYNC) && file &&
 				(vma->vm_flags & VM_SHARED)) {
 			get_file(file);
-			up_read(&current->mm->mmap_sem);
+			up_read(&mm->mmap_sem);
 			error = do_fsync(file, 0);
 			fput(file);
-			down_read(&current->mm->mmap_sem);
-			if (error)
-				goto out_unlock;
-			vma = find_vma(current->mm, start);
+			if (error || start >= end)
+				goto out;
+			down_read(&mm->mmap_sem);
+			vma = find_vma(mm, start);
 		} else {
+			if (start >= end)
+				goto out_unlock;
 			vma = vma->vm_next;
 		}
-	} while (vma && !done);
+	}
 out_unlock:
-	up_read(&current->mm->mmap_sem);
+	up_read(&mm->mmap_sem);
 out:
-	return error;
+	return error ? : unmapped_error;
 }
-
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