[PATCH 15/19] writeback: update wb_over_bg_thresh() to use wb_domain aware operations

Tejun Heo
2015-04-06T20:07:10Z

wb_over_bg_thresh() currently uses global_dirty_limits() and
wb_dirty_limit() both of which are wrappers around operations which
take dirty_throttle_control. For cgroup writeback support, the
function will be updated to also consider memcg wb_domains which
requires the context information carried in dirty_throttle_control.

This patch updates wb_over_bg_thresh() so that it uses the underlying
wb_domain aware operations directly and builds the global
dirty_throttle_control in the process.

This patch doesn't introduce any behavioral changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Greg Thelen <gthelen@google.com>
---
mm/page-writeback.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 1bc3a65..c08b053 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1749,15 +1749,22 @@ EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
*/
bool wb_over_bg_thresh(struct bdi_writeback *wb)
{
- unsigned long background_thresh, dirty_thresh;
+ struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
+ struct dirty_throttle_control * const gdtc = &gdtc_stor;

- global_dirty_limits(&background_thresh, &dirty_thresh);
+ /*
+ * Similar to balance_dirty_pages() but ignores pages being written
+ * as we're trying to decide whether to put more under writeback.
+ */
+ gdtc->avail = global_dirtyable_memory();
+ gdtc->dirty = global_page_state(NR_FILE_DIRTY) +
+ global_page_state(NR_UNSTABLE_NFS);
+ domain_dirty_limits(gdtc);

- if (global_page_state(NR_FILE_DIRTY) +
- global_page_state(NR_UNSTABLE_NFS) > background_thresh)
+ if (gdtc->dirty > gdtc->bg_thresh)
return true;

- if (wb_stat(wb, WB_RECLAIMABLE) > wb_calc_thresh(wb, background_thresh))
+ if (wb_stat(wb, WB_RECLAIMABLE) > __wb_calc_thresh(gdtc))
return true;

return false;
--
2.1.0