[PATCH -v5 2/2] Updating ctime and mtime at syncing

[Anton Salikhmetov <salikhmetov@gmail.com>]

http://bugzilla.kernel.org/show_bug.cgi?id=2645

Changes for updating the ctime and mtime fields for memory-mapped files:

1) a new flag triggering update of the inode data;
2) a new field in the address_space structure for saving modification time;
3) a new helper function to update ctime and mtime when needed;
4) updating time stamps for mapped files in sys_msync() and do_fsync();
5) implementing lazy ctime and mtime update.

Signed-off-by: Anton Salikhmetov <salikhmetov@gmail.com>
---
 fs/buffer.c             |    3 ++
 fs/fs-writeback.c       |    2 +
 fs/inode.c              |   43 +++++++++++++++++++++++----------
 fs/sync.c               |    2 +
 include/linux/fs.h      |   13 +++++++++-
 include/linux/pagemap.h |    3 +-
 mm/msync.c              |   61 +++++++++++++++++++++++++++++++++-------------
 mm/page-writeback.c     |   54 ++++++++++++++++++++++-------------------
 8 files changed, 124 insertions(+), 57 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 7249e01..3967aa7 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -701,6 +701,9 @@ static int __set_page_dirty(struct page *page,
 	if (unlikely(!mapping))
 		return !TestSetPageDirty(page);
 
+	mapping->mtime = CURRENT_TIME;
+	set_bit(AS_MCTIME, &mapping->flags);
+
 	if (TestSetPageDirty(page))
 		return 0;
 
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 300324b..affd291 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -243,6 +243,8 @@ __sync_single_inode(struct inode *inode, struct writeback_control *wbc)
 
 	spin_unlock(&inode_lock);
 
+	mapping_update_time(mapping);
+
 	ret = do_writepages(mapping, wbc);
 
 	/* Don't write the inode if only I_DIRTY_PAGES was set */
diff --git a/fs/inode.c b/fs/inode.c
index ed35383..edd5bf4 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1243,8 +1243,10 @@ void touch_atime(struct vfsmount *mnt, struct dentry *dentry)
 EXPORT_SYMBOL(touch_atime);
 
 /**
- *	file_update_time	-	update mtime and ctime time
- *	@file: file accessed
+ *	inode_update_time	-	update mtime and ctime time
+ *	@inode: inode accessed
+ *	@ts: time when inode was accessed
+ *	@sync: whether to do synchronous update
  *
  *	Update the mtime and ctime members of an inode and mark the inode
  *	for writeback.  Note that this function is meant exclusively for
@@ -1253,11 +1255,8 @@ EXPORT_SYMBOL(touch_atime);
  *	S_NOCTIME inode flag, e.g. for network filesystem where these
  *	timestamps are handled by the server.
  */
-
-void file_update_time(struct file *file)
+void inode_update_time(struct inode *inode, struct timespec *ts)
 {
-	struct inode *inode = file->f_path.dentry->d_inode;
-	struct timespec now;
 	int sync_it = 0;
 
 	if (IS_NOCMTIME(inode))
@@ -1265,22 +1264,41 @@ void file_update_time(struct file *file)
 	if (IS_RDONLY(inode))
 		return;
 
-	now = current_fs_time(inode->i_sb);
-	if (!timespec_equal(&inode->i_mtime, &now)) {
-		inode->i_mtime = now;
+	if (timespec_compare(&inode->i_mtime, ts) < 0) {
+		inode->i_mtime = *ts;
 		sync_it = 1;
 	}
 
-	if (!timespec_equal(&inode->i_ctime, &now)) {
-		inode->i_ctime = now;
+	if (timespec_compare(&inode->i_ctime, ts) < 0) {
+		inode->i_ctime = *ts;
 		sync_it = 1;
 	}
 
 	if (sync_it)
 		mark_inode_dirty_sync(inode);
 }
+EXPORT_SYMBOL(inode_update_time);
 
-EXPORT_SYMBOL(file_update_time);
+/*
+ * Update the ctime and mtime stamps after checking if they are to be updated.
+ */
+void mapping_update_time(struct address_space *mapping)
+{
+	if (test_and_clear_bit(AS_MCTIME, &mapping->flags)) {
+		struct inode *inode = mapping->host;
+		struct timespec *ts = &mapping->mtime;
+
+		if (S_ISBLK(inode->i_mode)) {
+			struct block_device *bdev = inode->i_bdev;
+
+			mutex_lock(&bdev->bd_mutex);
+			list_for_each_entry(inode, &bdev->bd_inodes, i_devices)
+				inode_update_time(inode, ts);
+			mutex_unlock(&bdev->bd_mutex);
+		} else
+			inode_update_time(inode, ts);
+	}
+}
 
 int inode_needs_sync(struct inode *inode)
 {
@@ -1290,7 +1308,6 @@ int inode_needs_sync(struct inode *inode)
 		return 1;
 	return 0;
 }
-
 EXPORT_SYMBOL(inode_needs_sync);
 
 int inode_wait(void *word)
diff --git a/fs/sync.c b/fs/sync.c
index 7cd005e..5561464 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -87,6 +87,8 @@ long do_fsync(struct file *file, int datasync)
 		goto out;
 	}
 
+	mapping_update_time(mapping);
+
 	ret = filemap_fdatawrite(mapping);
 
 	/*
diff --git a/include/linux/fs.h b/include/linux/fs.h
index b3ec4a4..f0d3ced 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -511,6 +511,7 @@ struct address_space {
 	spinlock_t		private_lock;	/* for use by the address_space */
 	struct list_head	private_list;	/* ditto */
 	struct address_space	*assoc_mapping;	/* ditto */
+	struct timespec		mtime;		/* modification time */
 } __attribute__((aligned(sizeof(long))));
 	/*
 	 * On most architectures that alignment is already the case; but
@@ -1977,7 +1978,17 @@ extern int buffer_migrate_page(struct address_space *,
 extern int inode_change_ok(struct inode *, struct iattr *);
 extern int __must_check inode_setattr(struct inode *, struct iattr *);
 
-extern void file_update_time(struct file *file);
+extern void inode_update_time(struct inode *, struct timespec *);
+
+static inline void file_update_time(struct file *file)
+{
+	struct inode *inode = file->f_dentry->d_inode;
+	struct timespec ts = current_fs_time(inode->i_sb);
+
+	inode_update_time(inode, &ts);
+}
+
+extern void mapping_update_time(struct address_space *);
 
 static inline ino_t parent_ino(struct dentry *dentry)
 {
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index db8a410..bf0f9e7 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -17,8 +17,9 @@
  * Bits in mapping->flags.  The lower __GFP_BITS_SHIFT bits are the page
  * allocation mode flags.
  */
-#define	AS_EIO		(__GFP_BITS_SHIFT + 0)	/* IO error on async write */
+#define AS_EIO		(__GFP_BITS_SHIFT + 0)	/* IO error on async write */
 #define AS_ENOSPC	(__GFP_BITS_SHIFT + 1)	/* ENOSPC on async write */
+#define AS_MCTIME	(__GFP_BITS_SHIFT + 2)	/* mtime and ctime to update */
 
 static inline void mapping_set_error(struct address_space *mapping, int error)
 {
diff --git a/mm/msync.c b/mm/msync.c
index 44997bf..7657776 100644
--- a/mm/msync.c
+++ b/mm/msync.c
@@ -13,16 +13,37 @@
 #include <linux/syscalls.h>
 
 /*
+ * Scan the PTEs for pages belonging to the VMA and mark them read-only.
+ * It will force a pagefault on the next write access.
+ */
+static void vma_wrprotect(struct vm_area_struct *vma)
+{
+	unsigned long addr;
+
+	for (addr = vma->vm_start; addr < vma->vm_end; addr += PAGE_SIZE) {
+		spinlock_t *ptl;
+		pgd_t *pgd = pgd_offset(vma->vm_mm, addr);
+		pud_t *pud = pud_offset(pgd, addr);
+		pmd_t *pmd = pmd_offset(pud, addr);
+		pte_t *pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
+
+		if (pte_dirty(*pte) && pte_write(*pte))
+			*pte = pte_wrprotect(*pte);
+		pte_unmap_unlock(pte, ptl);
+	}
+}
+
+/*
  * 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 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.
+ * MS_ASYNC does not start I/O. Instead, it marks the relevant pages
+ * read-only by calling vma_wrprotect(). This is needed to catch the next
+ * write reference to the mapped region and update the file times
+ * accordingly.
  *
- * 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.
  */
@@ -80,16 +101,22 @@ asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
 		start = vma->vm_end;
 
 		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);
-			fput(file);
-			if (error)
-				goto out;
-			down_read(&mm->mmap_sem);
-			vma = find_vma(mm, start);
-			continue;
+		if (file && (vma->vm_flags & VM_SHARED)) {
+			if (flags & MS_ASYNC) {
+				vma_wrprotect(vma);
+				mapping_update_time(file->f_mapping);
+			}
+			if (flags & MS_SYNC) {
+				get_file(file);
+				up_read(&mm->mmap_sem);
+				error = do_fsync(file, 0);
+				fput(file);
+				if (error)
+					goto out;
+				down_read(&mm->mmap_sem);
+				vma = find_vma(mm, start);
+				continue;
+			}
 		}
 
 		vma = vma->vm_next;
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 3d3848f..53d0e34 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -997,35 +997,39 @@ int __set_page_dirty_no_writeback(struct page *page)
  */
 int __set_page_dirty_nobuffers(struct page *page)
 {
-	if (!TestSetPageDirty(page)) {
-		struct address_space *mapping = page_mapping(page);
-		struct address_space *mapping2;
+	struct address_space *mapping = page_mapping(page);
+	struct address_space *mapping2;
 
-		if (!mapping)
-			return 1;
+	if (!mapping)
+		return 1;
 
-		write_lock_irq(&mapping->tree_lock);
-		mapping2 = page_mapping(page);
-		if (mapping2) { /* Race with truncate? */
-			BUG_ON(mapping2 != mapping);
-			WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
-			if (mapping_cap_account_dirty(mapping)) {
-				__inc_zone_page_state(page, NR_FILE_DIRTY);
-				__inc_bdi_stat(mapping->backing_dev_info,
-						BDI_RECLAIMABLE);
-				task_io_account_write(PAGE_CACHE_SIZE);
-			}
-			radix_tree_tag_set(&mapping->page_tree,
-				page_index(page), PAGECACHE_TAG_DIRTY);
-		}
-		write_unlock_irq(&mapping->tree_lock);
-		if (mapping->host) {
-			/* !PageAnon && !swapper_space */
-			__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
+	mapping->mtime = CURRENT_TIME;
+	set_bit(AS_MCTIME, &mapping->flags);
+
+	if (TestSetPageDirty(page))
+		return 0;
+
+	write_lock_irq(&mapping->tree_lock);
+	mapping2 = page_mapping(page);
+	if (mapping2) {
+		/* Race with truncate? */
+		BUG_ON(mapping2 != mapping);
+		WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
+		if (mapping_cap_account_dirty(mapping)) {
+			__inc_zone_page_state(page, NR_FILE_DIRTY);
+			__inc_bdi_stat(mapping->backing_dev_info,
+					BDI_RECLAIMABLE);
+			task_io_account_write(PAGE_CACHE_SIZE);
 		}
-		return 1;
+		radix_tree_tag_set(&mapping->page_tree,
+				page_index(page), PAGECACHE_TAG_DIRTY);
 	}
-	return 0;
+	write_unlock_irq(&mapping->tree_lock);
+
+	if (mapping->host)
+		__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
+
+	return 1;
 }
 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
 
-- 
1.4.4.4