[RFC 1/2] writeback: add support for filesystems to affine inodes to specific writeback ctx

[wangyufei <wangyufei@vivo.com>]

Introduce a new superblock operation get_inode_wb_ctx_idx() to allow
filesystems to decide how inodes are assigned to writeback contexts.
This helps optimize parallel writeback performance based on the
underlying filesystem architecture.

In fetch_bdi_writeback_ctx(), if this operation is implemented by the
filesystem, it will return a specific writeback context index for a
given inode. Otherwise fall back to the default way.

Signed-off-by: wangyufei <wangyufei@vivo.com>
---
 include/linux/backing-dev.h | 3 +++
 include/linux/fs.h          | 1 +
 2 files changed, 4 insertions(+)

diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index c93509f5e..d02536f6e 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -144,7 +144,10 @@ static inline struct bdi_writeback_ctx *
 fetch_bdi_writeback_ctx(struct inode *inode)
 {
 	struct backing_dev_info *bdi = inode_to_bdi(inode);
+	struct super_block *sb = inode->i_sb;
 
+	if (sb->s_op->get_inode_wb_ctx_idx)
+		return bdi->wb_ctx_arr[sb->s_op->get_inode_wb_ctx_idx(inode, bdi->nr_wb_ctx)];
 	return bdi->wb_ctx_arr[inode->i_ino % bdi->nr_wb_ctx];
 }
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 6c07228bd..fad7a75fd 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2491,6 +2491,7 @@ struct super_operations {
 	 */
 	int (*remove_bdev)(struct super_block *sb, struct block_device *bdev);
 	void (*shutdown)(struct super_block *sb);
+	unsigned int (*get_inode_wb_ctx_idx)(struct inode *inode, int nr_wb_ctx);
 };
 
 /*
-- 
2.34.1