Re: [PATCH 10/13] fuse: add support for multiple writeback contexts in fuse

[Christoph Hellwig <hch@lst.de>]

>  static void fuse_writepage_finish_stat(struct inode *inode, struct folio *folio)
>  {
> -	struct backing_dev_info *bdi = inode_to_bdi(inode);
> +	struct bdi_writeback_ctx *bdi_wb_ctx = fetch_bdi_writeback_ctx(inode);
>  
> -	dec_wb_stat(&bdi->wb_ctx_arr[0]->wb, WB_WRITEBACK);
> +	dec_wb_stat(&bdi_wb_ctx->wb, WB_WRITEBACK);
>  	node_stat_sub_folio(folio, NR_WRITEBACK_TEMP);
> -	wb_writeout_inc(&bdi->wb_ctx_arr[0]->wb);
> +	wb_writeout_inc(&bdi_wb_ctx->wb);
>  }

There's nothing fuse-specific here except that nothing but fuse uses
NR_WRITEBACK_TEMP.  Can we try to move this into the core first so that
the patches don't have to touch file system code?

> -	inc_wb_stat(&inode_to_bdi(inode)->wb_ctx_arr[0]->wb, WB_WRITEBACK);
> +	inc_wb_stat(&bdi_wb_ctx->wb, WB_WRITEBACK);
>  	node_stat_add_folio(tmp_folio, NR_WRITEBACK_TEMP);

Same here.  On pattern is that fuse and nfs both touch the node stat
and the web stat, and having a common helper doing both would probably
also be very helpful.