vfs: re-implement writeback_inodes_sb(_nr)_if_idle() and rename them

writeback_inodes_sb(_nr)_if_idle() is re-implemented by replacing down_read()
with down_read_trylock() because

- If ->s_umount is write locked, then the sb is not idle. That is
  writeback_inodes_sb(_nr)_if_idle() needn't wait for the lock.

- writeback_inodes_sb(_nr)_if_idle() grabs s_umount lock when it want to start
  writeback, it may bring us deadlock problem when doing umount. In order to
  fix the problem, ext4 and btrfs implemented their own writeback functions
  instead of writeback_inodes_sb(_nr)_if_idle(), but it introduced the redundant
  code, it is better to implement a new writeback_inodes_sb(_nr)_if_idle().

The name of these two functions is cumbersome, so rename them to
try_to_writeback_inodes_sb(_nr).

This idea came from Christoph Hellwig.
Some code is from the patch of Kamal Mostafa.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 521e9d4424f64f81d69d98709031a342d5ee808f..f31abb14e06f171054f182864acb1dabf6fd1335 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3689,20 +3689,6 @@ static int can_overcommit(struct btrfs_root *root,
        return 0;
 }
 
-static int writeback_inodes_sb_nr_if_idle_safe(struct super_block *sb,
-                                              unsigned long nr_pages,
-                                              enum wb_reason reason)
-{
-       if (!writeback_in_progress(sb->s_bdi) &&
-           down_read_trylock(&sb->s_umount)) {
-               writeback_inodes_sb_nr(sb, nr_pages, reason);
-               up_read(&sb->s_umount);
-               return 1;
-       }
-
-       return 0;
-}
-
 /*
  * shrink metadata reservation for delalloc
  */
@@ -3735,9 +3721,9 @@ static void shrink_delalloc(struct btrfs_root *root, u64 to_reclaim, u64 orig,
        while (delalloc_bytes && loops < 3) {
                max_reclaim = min(delalloc_bytes, to_reclaim);
                nr_pages = max_reclaim >> PAGE_CACHE_SHIFT;
-               writeback_inodes_sb_nr_if_idle_safe(root->fs_info->sb,
-                                                   nr_pages,
-                                                   WB_REASON_FS_FREE_SPACE);
+               try_to_writeback_inodes_sb_nr(root->fs_info->sb,
+                                             nr_pages,
+                                             WB_REASON_FS_FREE_SPACE);
 
                /*
                 * We need to wait for the async pages to actually start before

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index cbfe13bf5b2aa3f39b4845fe4fce4f45a02b5f43..5f6eef71ff214af0d29a40c2a276eaab41c08533 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2512,12 +2512,8 @@ static int ext4_nonda_switch(struct super_block *sb)
        /*
         * Start pushing delalloc when 1/2 of free blocks are dirty.
         */
-       if (dirty_blocks && (free_blocks < 2 * dirty_blocks) &&
-           !writeback_in_progress(sb->s_bdi) &&
-           down_read_trylock(&sb->s_umount)) {
-               writeback_inodes_sb(sb, WB_REASON_FS_FREE_SPACE);
-               up_read(&sb->s_umount);
-       }
+       if (dirty_blocks && (free_blocks < 2 * dirty_blocks))
+               try_to_writeback_inodes_sb(sb, WB_REASON_FS_FREE_SPACE);
 
        if (2 * free_blocks < 3 * dirty_blocks ||
                free_blocks < (dirty_blocks + EXT4_FREECLUSTERS_WATERMARK)) {

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 310972b72a6654c1597fc11f717954606561c47e..ad3cc46a743aa8c1b347af78a2615f7868659feb 100644 (file)
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1332,47 +1332,43 @@ void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
 EXPORT_SYMBOL(writeback_inodes_sb);
 
 /**
- * writeback_inodes_sb_if_idle -       start writeback if none underway
+ * try_to_writeback_inodes_sb_nr - try to start writeback if none underway
  * @sb: the superblock
- * @reason: reason why some writeback work was initiated
+ * @nr: the number of pages to write
+ * @reason: the reason of writeback
  *
- * Invoke writeback_inodes_sb if no writeback is currently underway.
+ * Invoke writeback_inodes_sb_nr if no writeback is currently underway.
  * Returns 1 if writeback was started, 0 if not.
  */
-int writeback_inodes_sb_if_idle(struct super_block *sb, enum wb_reason reason)
+int try_to_writeback_inodes_sb_nr(struct super_block *sb,
+                                 unsigned long nr,
+                                 enum wb_reason reason)
 {
-       if (!writeback_in_progress(sb->s_bdi)) {
-               down_read(&sb->s_umount);
-               writeback_inodes_sb(sb, reason);
-               up_read(&sb->s_umount);
+       if (writeback_in_progress(sb->s_bdi))
                return 1;
-       } else
+
+       if (!down_read_trylock(&sb->s_umount))
                return 0;
+
+       writeback_inodes_sb_nr(sb, nr, reason);
+       up_read(&sb->s_umount);
+       return 1;
 }
-EXPORT_SYMBOL(writeback_inodes_sb_if_idle);
+EXPORT_SYMBOL(try_to_writeback_inodes_sb_nr);
 
 /**
- * writeback_inodes_sb_nr_if_idle      -       start writeback if none underway
+ * try_to_writeback_inodes_sb - try to start writeback if none underway
  * @sb: the superblock
- * @nr: the number of pages to write
  * @reason: reason why some writeback work was initiated
  *
- * Invoke writeback_inodes_sb if no writeback is currently underway.
+ * Implement by try_to_writeback_inodes_sb_nr()
  * Returns 1 if writeback was started, 0 if not.
  */
-int writeback_inodes_sb_nr_if_idle(struct super_block *sb,
-                                  unsigned long nr,
-                                  enum wb_reason reason)
+int try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
 {
-       if (!writeback_in_progress(sb->s_bdi)) {
-               down_read(&sb->s_umount);
-               writeback_inodes_sb_nr(sb, nr, reason);
-               up_read(&sb->s_umount);
-               return 1;
-       } else
-               return 0;
+       return try_to_writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
 }
-EXPORT_SYMBOL(writeback_inodes_sb_nr_if_idle);
+EXPORT_SYMBOL(try_to_writeback_inodes_sb);
 
 /**
  * sync_inodes_sb      -       sync sb inode pages

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index b82a83aba31185870b132d4e8d7c99bb975fc0b6..9a9367c0c0768bff86bfa9ddde5ff85574497292 100644 (file)
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -87,9 +87,9 @@ int inode_wait(void *);
 void writeback_inodes_sb(struct super_block *, enum wb_reason reason);
 void writeback_inodes_sb_nr(struct super_block *, unsigned long nr,
                                                        enum wb_reason reason);
-int writeback_inodes_sb_if_idle(struct super_block *, enum wb_reason reason);
-int writeback_inodes_sb_nr_if_idle(struct super_block *, unsigned long nr,
-                                                       enum wb_reason reason);
+int try_to_writeback_inodes_sb(struct super_block *, enum wb_reason reason);
+int try_to_writeback_inodes_sb_nr(struct super_block *, unsigned long nr,
+                                 enum wb_reason reason);
 void sync_inodes_sb(struct super_block *);
 long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
                                enum wb_reason reason);