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Commit 0f6d24f8 authored by Yafang Shao's avatar Yafang Shao Committed by Linus Torvalds
Browse files

mm/page-writeback.c: print a warning if the vm dirtiness settings are illogical 

The vm direct limit setting must be set greater than vm background limit
setting.  Otherwise print a warning to help the operator to figure out
that the vm dirtiness settings is in illogical state.

Link: http://lkml.kernel.org/r/1506592464-30962-1-git-send-email-laoar.shao@gmail.com


Signed-off-by: default avatarYafang Shao <laoar.shao@gmail.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 66e8b438

Documentation/sysctl/vm.txt

+7 −0
Original line number Diff line number Diff line
@@ -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

mm/page-writeback.c

+4 −1
Original line number Diff line number Diff line
@@ -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;