[PATCH] mm: Fix memcg writeback for rt tasks

[PATCH] mm: Fix memcg writeback for rt tasks

[yizhou.tang]

From: Tang Yizhou <yizhou.tang@shopee.com>

Neil said he didn't know what was wanted for realtime in the commit
message of commit a37b0715ddf3 ("mm/writeback: replace PF_LESS_THROTTLE
with PF_LOCAL_THROTTLE"). I think we need to distinguish between the
global writeback and memcg writeback in domain_dirty_limits() for the
rt tasks.

Fixes: a53eaff8c119 ("MM: increase safety margin provided by PF_LESS_THROTTLE")
CC: NeilBrown <neilb@suse.com>
CC: Tejun Heo <tj@kernel.org>
CC: Fengguang Wu <wufengguang@huawei.com>
Signed-off-by: Tang Yizhou <yizhou.tang@shopee.com>
---
 mm/page-writeback.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 516b1aa247e8..7d92de73360e 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -419,8 +419,8 @@ static void domain_dirty_limits(struct dirty_throttle_control *dtc)
 		bg_thresh = thresh / 2;
 	tsk = current;
 	if (rt_task(tsk)) {
-		bg_thresh += bg_thresh / 4 + global_wb_domain.dirty_limit / 32;
-		thresh += thresh / 4 + global_wb_domain.dirty_limit / 32;
+		bg_thresh += bg_thresh / 4 + dtc_dom(dtc)->dirty_limit / 32;
+		thresh += thresh / 4 + dtc_dom(dtc)->dirty_limit / 32;
 	}
 	dtc->thresh = thresh;
 	dtc->bg_thresh = bg_thresh;
-- 
2.25.1

Re: [PATCH] mm: Fix memcg writeback for rt tasks

[Andrew Morton]

On Tue,  4 Apr 2023 00:57:08 +0800 yizhou.tang@shopee.com wrote:

> From: Tang Yizhou <yizhou.tang@shopee.com>
> 
> Neil said he didn't know what was wanted for realtime in the commit
> message of commit a37b0715ddf3 ("mm/writeback: replace PF_LESS_THROTTLE
> with PF_LOCAL_THROTTLE"). I think we need to distinguish between the
> global writeback and memcg writeback in domain_dirty_limits() for the
> rt tasks.

Why do you think this?

> Fixes: a53eaff8c119 ("MM: increase safety margin provided by PF_LESS_THROTTLE")

In what way does it fix it?  Please describe the user-visible effects
of this change.