[PATCH 25/49] writeback: let balance_dirty_pages() work on the matching cgroup bdi_writeback

Tejun Heo
2015-04-06T20:00:12Z

Currently, balance_dirty_pages() always work on bdi->wb. This patch
updates it to work on the wb (bdi_writeback) matching memcg and blkcg
of the current task as that's what the inode is being dirtied against.

balance_dirty_pages_ratelimited() now pins the current wb and passes
it to balance_dirty_pages().

As no filesystem has FS_CGROUP_WRITEBACK yet, this doesn't lead to
visible behavior differences.

v2: Updated for per-inode wb association.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
---
mm/page-writeback.c | 18 +++++++++++++-----
1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 3b6d058..0aa2ffe 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1337,6 +1337,7 @@ static inline void wb_dirty_limits(struct bdi_writeback *wb,
* perform some writeout.
*/
static void balance_dirty_pages(struct address_space *mapping,
+ struct bdi_writeback *wb,
unsigned long pages_dirtied)
{
unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */
@@ -1352,8 +1353,7 @@ static void balance_dirty_pages(struct address_space *mapping,
unsigned long task_ratelimit;
unsigned long dirty_ratelimit;
unsigned long pos_ratio;
- struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
- struct bdi_writeback *wb = &bdi->wb;
+ struct backing_dev_info *bdi = wb->bdi;
bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
unsigned long start_time = jiffies;

@@ -1575,14 +1575,20 @@ DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
*/
void balance_dirty_pages_ratelimited(struct address_space *mapping)
{
- struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
- struct bdi_writeback *wb = &bdi->wb;
+ struct inode *inode = mapping->host;
+ struct backing_dev_info *bdi = inode_to_bdi(inode);
+ struct bdi_writeback *wb = NULL;
int ratelimit;
int *p;

if (!bdi_cap_account_dirty(bdi))
return;

+ if (inode_cgwb_enabled(inode))
+ wb = wb_get_create_current(bdi, GFP_KERNEL);
+ if (!wb)
+ wb = &bdi->wb;
+
ratelimit = current->nr_dirtied_pause;
if (wb->dirty_exceeded)
ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
@@ -1616,7 +1622,9 @@ void balance_dirty_pages_ratelimited(struct address_space *mapping)
preempt_enable();

if (unlikely(current->nr_dirtied >= ratelimit))
- balance_dirty_pages(mapping, current->nr_dirtied);
+ balance_dirty_pages(mapping, wb, current->nr_dirtied);
+
+ wb_put(wb);
}
EXPORT_SYMBOL(balance_dirty_pages_ratelimited);

--
2.1.0