Merge patch series "Avoid filesystem references to writeback internals"

Kundan Kumar <kundan.kumar@samsung.com> says:

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/

* patches from https://patch.msgid.link/20260213054634.79785-1-kundan.kumar@samsung.com:
  nfs: stop using writeback internals for WB_WRITEBACK accounting
  gfs2: stop using writeback internals for dirty_exceeded check
  f2fs: stop using writeback internals for dirty_exceeded checks
  writeback: prep helpers for dirty-limit and writeback accounting

Link: https://patch.msgid.link/20260213054634.79785-1-kundan.kumar@samsung.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

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;

fs/f2fs/segment.h

@@ -992,7 +992,7 @@ 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)

fs/gfs2/super.c

@@ -449,7 +449,7 @@ 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);

fs/nfs/internal.h

@@ -859,7 +859,7 @@ 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, WB_WRITEBACK, nr);
 		__mark_inode_dirty(inode, I_DIRTY_DATASYNC);
 	}
 }

fs/nfs/write.c

@@ -872,8 +872,7 @@ 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(folio->mapping->host, WB_WRITEBACK, -nr);
 	}
 }
 

include/linux/backing-dev.h

@@ -136,6 +136,19 @@ static inline bool mapping_can_writeback(struct address_space *mapping)
 	return inode_to_bdi(mapping->host)->capabilities & BDI_CAP_WRITEBACK;
 }
 
+/* Must not be used by file systems that support cgroup writeback */
+static inline int bdi_wb_dirty_exceeded(struct backing_dev_info *bdi)
+{
+	return bdi->wb.dirty_exceeded;
+}
+
+/* Must not be used by file systems that support cgroup writeback */
+static inline void bdi_wb_stat_mod(struct inode *inode, enum wb_stat_item item,
+				   s64 amount)
+{
+	wb_stat_mod(&inode_to_bdi(inode)->wb, item, amount);
+}
+
 #ifdef CONFIG_CGROUP_WRITEBACK
 
 struct bdi_writeback *wb_get_lookup(struct backing_dev_info *bdi,