Re: [PATCH V2] vfs: re-implement writeback_inodes_sb(_nr)_if_idle() and rename them

2013-01-11 Thread Fengguang Wu 
On Fri, Jan 11, 2013 at 09:12:11PM +0100, Jan Kara wrote:
> On Thu 10-01-13 13:47:57, Miao Xie wrote:
> > 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.
>   The patch looks good. Thanks! You can add:
> Reviewed-by: Jan Kara 
> 
>   BTW, since changes to filesystems are minimal, maybe Fengguang can take
> the patch through his writeback tree? Fengguang?

OK, done. The patch looks good, thanks!

Fengguang
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Re: [PATCH V2] vfs: re-implement writeback_inodes_sb(_nr)_if_idle() and rename them

2013-01-11 Thread Jan Kara 
On Thu 10-01-13 13:47:57, Miao Xie wrote:
> 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.
  The patch looks good. Thanks! You can add:
Reviewed-by: Jan Kara 

  BTW, since changes to filesystems are minimal, maybe Fengguang can take
the patch through his writeback tree? Fengguang?

Honza
> 
> Signed-off-by: Miao Xie 
> ---
> Changelog v1 -> v2:
> - do not remove EXPORT_SYMBOL of writeback_inodes_sb_br()
> ---
>  fs/btrfs/extent-tree.c| 20 +++-
>  fs/ext4/inode.c   |  8 ++--
>  fs/fs-writeback.c | 44 
>  include/linux/writeback.h |  6 +++---
>  4 files changed, 28 insertions(+), 50 deletions(-)
> 
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 521e9d4..f31abb1 100644
> --- 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(>s_umount)) {
> - writeback_inodes_sb_nr(sb, nr_pages, reason);
> - up_read(>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 cbfe13b..5f6eef7 100644
> --- 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(>s_umount)) {
> - writeback_inodes_sb(sb, WB_REASON_FS_FREE_SPACE);
> - up_read(>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 310972b..ad3cc46 100644
> --- 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,
>

Re: [PATCH V2] vfs: re-implement writeback_inodes_sb(_nr)_if_idle() and rename them

2013-01-11 Thread Jan Kara 
On Thu 10-01-13 13:47:57, Miao Xie wrote:
 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.
  The patch looks good. Thanks! You can add:
Reviewed-by: Jan Kara j...@suse.cz

  BTW, since changes to filesystems are minimal, maybe Fengguang can take
the patch through his writeback tree? Fengguang?

Honza
 
 Signed-off-by: Miao Xie mi...@cn.fujitsu.com
 ---
 Changelog v1 - v2:
 - do not remove EXPORT_SYMBOL of writeback_inodes_sb_br()
 ---
  fs/btrfs/extent-tree.c| 20 +++-
  fs/ext4/inode.c   |  8 ++--
  fs/fs-writeback.c | 44 
  include/linux/writeback.h |  6 +++---
  4 files changed, 28 insertions(+), 50 deletions(-)
 
 diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
 index 521e9d4..f31abb1 100644
 --- 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 cbfe13b..5f6eef7 100644
 --- 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 310972b..ad3cc46 100644
 --- 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

Re: [PATCH V2] vfs: re-implement writeback_inodes_sb(_nr)_if_idle() and rename them

2013-01-11 Thread Fengguang Wu 
On Fri, Jan 11, 2013 at 09:12:11PM +0100, Jan Kara wrote:
 On Thu 10-01-13 13:47:57, Miao Xie wrote:
  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.
   The patch looks good. Thanks! You can add:
 Reviewed-by: Jan Kara j...@suse.cz
 
   BTW, since changes to filesystems are minimal, maybe Fengguang can take
 the patch through his writeback tree? Fengguang?

OK, done. The patch looks good, thanks!

Fengguang
--
To unsubscribe from this list: send the line unsubscribe linux-kernel in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[PATCH V2] vfs: re-implement writeback_inodes_sb(_nr)_if_idle() and rename them

2013-01-09 Thread Miao Xie 
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.

Signed-off-by: Miao Xie 
---
Changelog v1 -> v2:
- do not remove EXPORT_SYMBOL of writeback_inodes_sb_br()
---
 fs/btrfs/extent-tree.c| 20 +++-
 fs/ext4/inode.c   |  8 ++--
 fs/fs-writeback.c | 44 
 include/linux/writeback.h |  6 +++---
 4 files changed, 28 insertions(+), 50 deletions(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 521e9d4..f31abb1 100644
--- 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(>s_umount)) {
-   writeback_inodes_sb_nr(sb, nr_pages, reason);
-   up_read(>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 cbfe13b..5f6eef7 100644
--- 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(>s_umount)) {
-   writeback_inodes_sb(sb, WB_REASON_FS_FREE_SPACE);
-   up_read(>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 310972b..ad3cc46 100644
--- 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(>s_umount);
-   writeback_inodes_sb(sb, reason);
-   up_read(>s_umount);
+   if (writeback_in_progress(sb->s_bdi))
return 1;
-   } else
+
+   if (!down_read_trylock(>s_umount))
return 0;
+
+   writeback_inodes_sb_nr(sb, nr, reason);
+   up_read(>s_umount);
+

[PATCH V2] vfs: re-implement writeback_inodes_sb(_nr)_if_idle() and rename them

2013-01-09 Thread Miao Xie 
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.

Signed-off-by: Miao Xie mi...@cn.fujitsu.com
---
Changelog v1 - v2:
- do not remove EXPORT_SYMBOL of writeback_inodes_sb_br()
---
 fs/btrfs/extent-tree.c| 20 +++-
 fs/ext4/inode.c   |  8 ++--
 fs/fs-writeback.c | 44 
 include/linux/writeback.h |  6 +++---
 4 files changed, 28 insertions(+), 50 deletions(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 521e9d4..f31abb1 100644
--- 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 cbfe13b..5f6eef7 100644
--- 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 310972b..ad3cc46 100644
--- 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);
+