The vm direct limit setting must be set greater than vm background
limit setting.
Otherwise we will print a warning to help the operator to figure
out that the vm dirtiness settings is in illogical state.
Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
---
Documentation/sysctl/vm.txt | 7 +++++++
mm/page-writeback.c | 5 ++++-
2 files changed, 11 insertions(+), 1 deletion(-)
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index 9baf66a..30fd16b 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -157,6 +157,10 @@ Note: the minimum value allowed for dirty_bytes is two pages (in bytes); any
value lower than this limit will be ignored and the old configuration will be
retained.
+Note: the value of dirty_bytes also must be set greater than
+dirty_background_bytes or the amount of memory corresponding to
+dirty_background_ratio.
+
==============================================================
dirty_expire_centisecs
@@ -176,6 +180,9 @@ generating disk writes will itself start writing out dirty data.
The total available memory is not equal to total system memory.
+Note: dirty_ratio must be set greater than dirty_background_ratio or
+ratio corresponding to dirty_background_bytes.
+
==============================================================
dirty_writeback_centisecs
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 0b9c5cb..8b747dd 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -433,8 +433,11 @@ static void domain_dirty_limits(struct dirty_throttle_control *dtc)
else
bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE;
- if (bg_thresh >= thresh)
+ if (unlikely(bg_thresh >= thresh)) {
+ pr_warn("vm direct limit must be set greater than background limit.\n");
bg_thresh = thresh / 2;
+ }
+
tsk = current;
if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
bg_thresh += bg_thresh / 4 + global_wb_domain.dirty_limit / 32;
--
1.8.3.1
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