[RFC][PATCH v7 13/14] writeback: make background writeback cgroup aware

[Greg Thelen <gthelen@google.com>]

When the system is under background dirty memory threshold but a cgroup
is over its background dirty memory threshold, then only writeback
inodes associated with the over-limit cgroup(s).

In addition to checking if the system dirty memory usage is over the
system background threshold, over_bground_thresh() also checks if any
cgroups are over their respective background dirty memory thresholds.
The writeback_control.for_cgroup field is set to distinguish between a
system and memcg overage.

If performing cgroup writeback, move_expired_inodes() skips inodes that
do not contribute dirty pages to the cgroup being written back.

After writing some pages, wb_writeback() will call
mem_cgroup_writeback_done() to update the set of over-bg-limits memcg.

Signed-off-by: Greg Thelen <gthelen@google.com>
---
 fs/fs-writeback.c |   31 +++++++++++++++++++++++--------
 1 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 0174fcf..b01bb2a 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -256,14 +256,17 @@ static void move_expired_inodes(struct list_head *delaying_queue,
 	LIST_HEAD(tmp);
 	struct list_head *pos, *node;
 	struct super_block *sb = NULL;
-	struct inode *inode;
+	struct inode *inode, *tmp_inode;
 	int do_sb_sort = 0;
 
-	while (!list_empty(delaying_queue)) {
-		inode = wb_inode(delaying_queue->prev);
+	list_for_each_entry_safe_reverse(inode, tmp_inode, delaying_queue,
+					 i_wb_list) {
 		if (wbc->older_than_this &&
 		    inode_dirtied_after(inode, *wbc->older_than_this))
 			break;
+		if (wbc->for_cgroup &&
+		    !should_writeback_mem_cgroup_inode(inode, wbc))
+			continue;
 		if (sb && sb != inode->i_sb)
 			do_sb_sort = 1;
 		sb = inode->i_sb;
@@ -614,14 +617,21 @@ void writeback_inodes_wb(struct bdi_writeback *wb,
  */
 #define MAX_WRITEBACK_PAGES     1024
 
-static inline bool over_bground_thresh(void)
+static inline bool over_bground_thresh(struct bdi_writeback *wb,
+				       struct writeback_control *wbc)
 {
 	unsigned long background_thresh, dirty_thresh;
 
 	global_dirty_limits(&background_thresh, &dirty_thresh);
 
-	return (global_page_state(NR_FILE_DIRTY) +
-		global_page_state(NR_UNSTABLE_NFS) > background_thresh);
+	if (global_page_state(NR_FILE_DIRTY) +
+	    global_page_state(NR_UNSTABLE_NFS) > background_thresh) {
+		wbc->for_cgroup = 0;
+		return true;
+	}
+
+	wbc->for_cgroup = 1;
+	return mem_cgroups_over_bground_dirty_thresh();
 }
 
 /*
@@ -700,7 +710,7 @@ static long wb_writeback(struct bdi_writeback *wb,
 		 * For background writeout, stop when we are below the
 		 * background dirty threshold
 		 */
-		if (work->for_background && !over_bground_thresh())
+		if (work->for_background && !over_bground_thresh(wb, &wbc))
 			break;
 
 		if (work->for_kupdate || work->for_background) {
@@ -729,6 +739,9 @@ retry:
 		work->nr_pages -= write_chunk - wbc.nr_to_write;
 		wrote += write_chunk - wbc.nr_to_write;
 
+		if (write_chunk - wbc.nr_to_write > 0)
+			mem_cgroup_writeback_done();
+
 		/*
 		 * Did we write something? Try for more
 		 *
@@ -809,7 +822,9 @@ static unsigned long get_nr_dirty_pages(void)
 
 static long wb_check_background_flush(struct bdi_writeback *wb)
 {
-	if (over_bground_thresh()) {
+	struct writeback_control wbc;
+
+	if (over_bground_thresh(wb, &wbc)) {
 
 		struct wb_writeback_work work = {
 			.nr_pages	= LONG_MAX,
-- 
1.7.3.1

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