[PATCH 0/4] Avoid filesystem references to writeback internals

[PATCH 0/4] Avoid filesystem references to writeback internals

[Kundan Kumar]

The series introduces writeback helper APIs and converts f2fs, gfs2
and nfs to stop accessing writeback internals directly.

As suggested by Christoph [1], filesystem code that directly accesses
writeback internals is split out:
[1] https://lore.kernel.org/all/20251015072912.GA11294@lst.de/

No functional changes intended

Kundan Kumar (4):
  writeback: prep helpers for dirty-limit and writeback accounting
  f2fs: stop using writeback internals for dirty_exceeded checks
  gfs2: stop using writeback internals for dirty_exceeded check
  nfs: stop using writeback internals for WB_WRITEBACK accounting

 fs/f2fs/node.c              |  4 ++--
 fs/f2fs/segment.h           |  2 +-
 fs/gfs2/super.c             |  2 +-
 fs/nfs/internal.h           |  2 +-
 fs/nfs/write.c              |  4 ++--
 include/linux/backing-dev.h | 11 +++++++++++
 6 files changed, 18 insertions(+), 7 deletions(-)


base-commit: 05f7e89ab9731565d8a62e3b5d1ec206485eeb0b
-- 
2.25.1

[PATCH 1/4] writeback: prep helpers for dirty-limit and writeback accounting

[Kundan Kumar]

Add helper APIs needed by filesystems to avoid poking into writeback
internals.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Kundan Kumar <kundan.kumar@samsung.com>
Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
---
 include/linux/backing-dev.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 0c8342747cab..4165ad3ddf00 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -78,6 +78,17 @@ static inline s64 wb_stat_sum(struct bdi_writeback *wb, enum wb_stat_item item)
 
 extern void wb_writeout_inc(struct bdi_writeback *wb);
 
+static inline int bdi_wb_dirty_exceeded(struct backing_dev_info *bdi)
+{
+	return bdi->wb.dirty_exceeded;
+}
+
+static inline void bdi_wb_stat_mod(struct backing_dev_info *bdi,
+				   enum wb_stat_item item, s64 amount)
+{
+	wb_stat_mod(&bdi->wb, item, amount);
+}
+
 /*
  * maximal error of a stat counter.
  */
-- 
2.25.1

Re: [PATCH 1/4] writeback: prep helpers for dirty-limit and writeback accounting

[Jan Kara]

On Wed 11-02-26 12:30:54, Kundan Kumar wrote:
> Add helper APIs needed by filesystems to avoid poking into writeback
> internals.
> 
> Suggested-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Kundan Kumar <kundan.kumar@samsung.com>
> Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>

Looks sensible. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  include/linux/backing-dev.h | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
> index 0c8342747cab..4165ad3ddf00 100644
> --- a/include/linux/backing-dev.h
> +++ b/include/linux/backing-dev.h
> @@ -78,6 +78,17 @@ static inline s64 wb_stat_sum(struct bdi_writeback *wb, enum wb_stat_item item)
>  
>  extern void wb_writeout_inc(struct bdi_writeback *wb);
>  
> +static inline int bdi_wb_dirty_exceeded(struct backing_dev_info *bdi)
> +{
> +	return bdi->wb.dirty_exceeded;
> +}
> +
> +static inline void bdi_wb_stat_mod(struct backing_dev_info *bdi,
> +				   enum wb_stat_item item, s64 amount)
> +{
> +	wb_stat_mod(&bdi->wb, item, amount);
> +}
> +
>  /*
>   * maximal error of a stat counter.
>   */
> -- 
> 2.25.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

[PATCH 2/4] f2fs: stop using writeback internals for dirty_exceeded checks

[Kundan Kumar]

Replace direct dereferences of dirty_exceeded with the core helper
bdi_wb_dirty_exceeded(), removing f2fs dependencies on writeback
internals.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Kundan Kumar <kundan.kumar@samsung.com>
Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
---
 fs/f2fs/node.c    | 4 ++--
 fs/f2fs/segment.h | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index 482a362f2625..d450b282cc55 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -78,7 +78,7 @@ bool f2fs_available_free_memory(struct f2fs_sb_info *sbi, int type)
 		if (excess_cached_nats(sbi))
 			res = false;
 	} else if (type == DIRTY_DENTS) {
-		if (sbi->sb->s_bdi->wb.dirty_exceeded)
+		if (bdi_wb_dirty_exceeded(sbi->sb->s_bdi))
 			return false;
 		mem_size = get_pages(sbi, F2FS_DIRTY_DENTS);
 		res = mem_size < ((avail_ram * nm_i->ram_thresh / 100) >> 1);
@@ -119,7 +119,7 @@ bool f2fs_available_free_memory(struct f2fs_sb_info *sbi, int type)
 		res = false;
 #endif
 	} else {
-		if (!sbi->sb->s_bdi->wb.dirty_exceeded)
+		if (!bdi_wb_dirty_exceeded(sbi->sb->s_bdi))
 			return true;
 	}
 	return res;
diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
index 07dcbcbeb7c6..d7166f1f000a 100644
--- a/fs/f2fs/segment.h
+++ b/fs/f2fs/segment.h
@@ -1000,7 +1000,7 @@ static inline bool sec_usage_check(struct f2fs_sb_info *sbi, unsigned int secno)
  */
 static inline int nr_pages_to_skip(struct f2fs_sb_info *sbi, int type)
 {
-	if (sbi->sb->s_bdi->wb.dirty_exceeded)
+	if (bdi_wb_dirty_exceeded(sbi->sb->s_bdi))
 		return 0;
 
 	if (type == DATA)
-- 
2.25.1

[PATCH 3/4] gfs2: stop using writeback internals for dirty_exceeded check

[Kundan Kumar]

Convert gfs2 dirty_exceeded handling to use the writeback core helper
instead of accessing writeback directly.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Kundan Kumar <kundan.kumar@samsung.com>
Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
---
 fs/gfs2/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index f6cd907b3ec6..7ddeee19dec4 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -447,7 +447,7 @@ static int gfs2_write_inode(struct inode *inode, struct writeback_control *wbc)
 		gfs2_log_flush(GFS2_SB(inode), ip->i_gl,
 			       GFS2_LOG_HEAD_FLUSH_NORMAL |
 			       GFS2_LFC_WRITE_INODE);
-	if (bdi->wb.dirty_exceeded)
+	if (bdi_wb_dirty_exceeded(bdi))
 		gfs2_ail1_flush(sdp, wbc);
 	else
 		filemap_fdatawrite(metamapping);
-- 
2.25.1

[PATCH 4/4] nfs: stop using writeback internals for WB_WRITEBACK accounting

[Kundan Kumar]

Convert NFS WB_WRITEBACK accounting to bdi-scoped writeback helper,
eliminating direct access to writeback.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Kundan Kumar <kundan.kumar@samsung.com>
Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
---
 fs/nfs/internal.h | 2 +-
 fs/nfs/write.c    | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
index 2e596244799f..a738c357b153 100644
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -866,7 +866,7 @@ static inline void nfs_folio_mark_unstable(struct folio *folio,
 		 * writeback is happening on the server now.
 		 */
 		node_stat_mod_folio(folio, NR_WRITEBACK, nr);
-		wb_stat_mod(&inode_to_bdi(inode)->wb, WB_WRITEBACK, nr);
+		bdi_wb_stat_mod(inode_to_bdi(inode), WB_WRITEBACK, nr);
 		__mark_inode_dirty(inode, I_DIRTY_DATASYNC);
 	}
 }
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index bf412455e8ed..c56b15b5380f 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -872,8 +872,8 @@ static void nfs_folio_clear_commit(struct folio *folio)
 		long nr = folio_nr_pages(folio);
 
 		node_stat_mod_folio(folio, NR_WRITEBACK, -nr);
-		wb_stat_mod(&inode_to_bdi(folio->mapping->host)->wb,
-			    WB_WRITEBACK, -nr);
+		bdi_wb_stat_mod(inode_to_bdi(folio->mapping->host),
+				WB_WRITEBACK, -nr);
 	}
 }
 
-- 
2.25.1

Re: [PATCH 0/4] Avoid filesystem references to writeback internals

[Jeff Layton]

On Wed, 2026-02-11 at 12:30 +0530, Kundan Kumar wrote:
> The series introduces writeback helper APIs and converts f2fs, gfs2
> and nfs to stop accessing writeback internals directly.
> 
> As suggested by Christoph [1], filesystem code that directly accesses
> writeback internals is split out:
> [1] https://lore.kernel.org/all/20251015072912.GA11294@lst.de/
> 
> No functional changes intended
> 
> Kundan Kumar (4):
>   writeback: prep helpers for dirty-limit and writeback accounting
>   f2fs: stop using writeback internals for dirty_exceeded checks
>   gfs2: stop using writeback internals for dirty_exceeded check
>   nfs: stop using writeback internals for WB_WRITEBACK accounting
> 
>  fs/f2fs/node.c              |  4 ++--
>  fs/f2fs/segment.h           |  2 +-
>  fs/gfs2/super.c             |  2 +-
>  fs/nfs/internal.h           |  2 +-
>  fs/nfs/write.c              |  4 ++--
>  include/linux/backing-dev.h | 11 +++++++++++
>  6 files changed, 18 insertions(+), 7 deletions(-)
> 
> 
> base-commit: 05f7e89ab9731565d8a62e3b5d1ec206485eeb0b

Seems sensible.

Reviewed-by: Jeff Layton <jlayton@kernel.org>

Re: [PATCH 0/4] Avoid filesystem references to writeback internals

[Andreas Gruenbacher]

On Wed, Feb 11, 2026 at 8:13 AM Kundan Kumar <kundan.kumar@samsung.com> wrote:
> The series introduces writeback helper APIs and converts f2fs, gfs2
> and nfs to stop accessing writeback internals directly.
>
> As suggested by Christoph [1], filesystem code that directly accesses
> writeback internals is split out:
> [1] https://lore.kernel.org/all/20251015072912.GA11294@lst.de/
>
> No functional changes intended
>
> Kundan Kumar (4):
>   writeback: prep helpers for dirty-limit and writeback accounting
>   f2fs: stop using writeback internals for dirty_exceeded checks
>   gfs2: stop using writeback internals for dirty_exceeded check
>   nfs: stop using writeback internals for WB_WRITEBACK accounting
>
>  fs/f2fs/node.c              |  4 ++--
>  fs/f2fs/segment.h           |  2 +-
>  fs/gfs2/super.c             |  2 +-
>  fs/nfs/internal.h           |  2 +-
>  fs/nfs/write.c              |  4 ++--
>  include/linux/backing-dev.h | 11 +++++++++++
>  6 files changed, 18 insertions(+), 7 deletions(-)
>
>
> base-commit: 05f7e89ab9731565d8a62e3b5d1ec206485eeb0b

Sure, that won't hurt.

Reviewed-by: Andreas Gruenbacher <agruenba@redhat.com>

Re: [PATCH 0/4] Avoid filesystem references to writeback internals

[Christoph Hellwig]

Looks fine as a cleanup, but maybe add comments that these functions
must not be used by file systems that support cgroup writeback and
thus can have multiple bdi_writeback structures per bdi?