From 6cc4c3aa714bc58ec5d20f3054ca5f23534984d1 Mon Sep 17 00:00:00 2001 From: Tang Yizhou Date: Tue, 4 Mar 2025 19:03:18 +0800 Subject: [PATCH] writeback: fix calculations in trace_balance_dirty_pages() for cgwb In the commit dcc25ae76eb7 ("writeback: move global_dirty_limit into wb_domain") of the cgroup writeback backpressure propagation patchset, Tejun made some adaptations to trace_balance_dirty_pages() for cgroup writeback. However, this adaptation was incomplete and Tejun missed further adaptation in the subsequent patches. In the cgroup writeback scenario, if sdtc in balance_dirty_pages() is assigned to mdtc, then upon entering trace_balance_dirty_pages(), __entry->limit should be assigned based on the dirty_limit of the corresponding memcg's wb_domain, rather than global_wb_domain. To address this issue and simplify the implementation, introduce a 'limit' field in struct dirty_throttle_control to store the hard_limit value computed in wb_position_ratio() by calling hard_dirty_limit(). This field will then be used in trace_balance_dirty_pages() to assign the value to __entry->limit. Link: https://lkml.kernel.org/r/20250304110318.159567-4-yizhou.tang@shopee.com Fixes: dcc25ae76eb7 ("writeback: move global_dirty_limit into wb_domain") Signed-off-by: Tang Yizhou Acked-by: Tejun Heo Cc: Alexei Starovoitov Cc: Christian Brauner Cc: Jan Kara Cc: "Masami Hiramatsu (Google)" Cc: Matthew Wilcow (Oracle) Cc: Steven Rostedt Signed-off-by: Andrew Morton --- include/linux/writeback.h | 1 + include/trace/events/writeback.h | 5 ++--- mm/page-writeback.c | 2 +- 3 files changed, 4 insertions(+), 4 deletions(-) diff --git a/include/linux/writeback.h b/include/linux/writeback.h index 32095928365c..58bda3347914 100644 --- a/include/linux/writeback.h +++ b/include/linux/writeback.h @@ -326,6 +326,7 @@ struct dirty_throttle_control { unsigned long dirty; /* file_dirty + write + nfs */ unsigned long thresh; /* dirty threshold */ unsigned long bg_thresh; /* dirty background threshold */ + unsigned long limit; /* hard dirty limit */ unsigned long wb_dirty; /* per-wb counterparts */ unsigned long wb_thresh; diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h index 3046ca6b08ea..0ff388131fc9 100644 --- a/include/trace/events/writeback.h +++ b/include/trace/events/writeback.h @@ -663,9 +663,8 @@ TRACE_EVENT(balance_dirty_pages, unsigned long freerun = (dtc->thresh + dtc->bg_thresh) / 2; strscpy_pad(__entry->bdi, bdi_dev_name(wb->bdi), 32); - __entry->limit = global_wb_domain.dirty_limit; - __entry->setpoint = (global_wb_domain.dirty_limit + - freerun) / 2; + __entry->limit = dtc->limit; + __entry->setpoint = (dtc->limit + freerun) / 2; __entry->dirty = dtc->dirty; __entry->wb_setpoint = __entry->setpoint * dtc->wb_thresh / (dtc->thresh + 1); diff --git a/mm/page-writeback.c b/mm/page-writeback.c index 149f8b815904..18456ddd463b 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -1072,7 +1072,7 @@ static void wb_position_ratio(struct dirty_throttle_control *dtc) struct bdi_writeback *wb = dtc->wb; unsigned long write_bw = READ_ONCE(wb->avg_write_bandwidth); unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh); - unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh); + unsigned long limit = dtc->limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh); unsigned long wb_thresh = dtc->wb_thresh; unsigned long x_intercept; unsigned long setpoint; /* dirty pages' target balance point */