writeback: rename nr_reclaimable to nr_dirty in balance_dirty_pages

Commit 8d92890b ("mm/writeback: discard NR_UNSTABLE_NFS, use
NR_WRITEBACK instead") removed NR_UNSTABLE_NFS and nr_reclaimable only
contains dirty page now.  Rename nr_reclaimable to nr_dirty properly.

Link: https://lkml.kernel.org/r/20240423034643.141219-6-shikemeng@huaweicloud.comSigned-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Brian Foster <bfoster@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: David Sterba <dsterba@suse.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: SeongJae Park <sj@kernel.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page-writeback.c

@@ -1694,7 +1694,7 @@ static int balance_dirty_pages(struct bdi_writeback *wb,
 	struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
 						     &mdtc_stor : NULL;
 	struct dirty_throttle_control *sdtc;
-	unsigned long nr_reclaimable;	/* = file_dirty */
+	unsigned long nr_dirty;
 	long period;
 	long pause;
 	long max_pause;
@@ -1715,9 +1715,9 @@ static int balance_dirty_pages(struct bdi_writeback *wb,
 		unsigned long m_thresh = 0;
 		unsigned long m_bg_thresh = 0;
 
-		nr_reclaimable = global_node_page_state(NR_FILE_DIRTY);
+		nr_dirty = global_node_page_state(NR_FILE_DIRTY);
 		gdtc->avail = global_dirtyable_memory();
-		gdtc->dirty = nr_reclaimable + global_node_page_state(NR_WRITEBACK);
+		gdtc->dirty = nr_dirty + global_node_page_state(NR_WRITEBACK);
 
 		domain_dirty_limits(gdtc);
 
@@ -1768,7 +1768,7 @@ static int balance_dirty_pages(struct bdi_writeback *wb,
 		 * In normal mode, we start background writeout at the lower
 		 * background_thresh, to keep the amount of dirty memory low.
 		 */
-		if (!laptop_mode && nr_reclaimable > gdtc->bg_thresh &&
+		if (!laptop_mode && nr_dirty > gdtc->bg_thresh &&
 		    !writeback_in_progress(wb))
 			wb_start_background_writeback(wb);