2017-11-26 16:03 GMT+08:00 Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>:
> Yafang Shao wrote:
>> >> I have also verified your test code on my machine, but can not find
>> >> this message.
>> >>
>> >
>> > Not always printed. It is timing dependent.
>> >
>>
>> I will try and analysis why this happen.
>>
> I see.
>
> Here is dump of variables. Always mostly 0 when this happens.
>
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -434,7 +434,8 @@ static void domain_dirty_limits(struct dirty_throttle_control *dtc)
> bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE;
>
> if (unlikely(bg_thresh >= thresh)) {
> - pr_warn("vm direct limit must be set greater than background limit.\n");
> + pr_warn("vm direct limit must be set greater than background limit. bg_thresh=%lu thresh=%lu bg_bytes=%lu bytes=%lu bg_ratio=%lu ratio=%lu gdtc=%p gdtc->vail=%lu vm_dirty_bytes=%lu dirty_background_bytes=%lu\n",
> + bg_thresh, thresh, bg_bytes, bytes, bg_ratio, ratio, gdtc, gdtc ? gdtc->avail : 0UL, vm_dirty_bytes, dirty_background_bytes);
> bg_thresh = thresh / 2;
> }
>
> [ 259.641324] vm direct limit must be set greater than background limit. bg_thresh=0 thresh=0 bg_bytes=0 bytes=0 bg_ratio=409 ratio=1228 gdtc= (null) gdtc->vail=0 vm_dirty_bytes=0 dirty_background_bytes=0
> [ 317.798913] vm direct limit must be set greater than background limit. bg_thresh=0 thresh=0 bg_bytes=0 bytes=0 bg_ratio=409 ratio=1228 gdtc= (null) gdtc->vail=0 vm_dirty_bytes=0 dirty_background_bytes=0
> [ 317.798935] vm direct limit must be set greater than background limit. bg_thresh=0 thresh=0 bg_bytes=0 bytes=0 bg_ratio=409 ratio=1228 gdtc= (null) gdtc->vail=0 vm_dirty_bytes=0 dirty_background_bytes=0
> [ 317.976210] vm direct limit must be set greater than background limit. bg_thresh=0 thresh=0 bg_bytes=0 bytes=0 bg_ratio=409 ratio=1228 gdtc= (null) gdtc->vail=0 vm_dirty_bytes=0 dirty_background_bytes=0
> [ 417.781194] vm direct limit must be set greater than background limit. bg_thresh=0 thresh=0 bg_bytes=0 bytes=0 bg_ratio=409 ratio=1228 gdtc= (null) gdtc->vail=0 vm_dirty_bytes=0 dirty_background_bytes=0
> [ 466.322615] vm direct limit must be set greater than background limit. bg_thresh=0 thresh=0 bg_bytes=0 bytes=0 bg_ratio=409 ratio=1228 gdtc= (null) gdtc->vail=0 vm_dirty_bytes=0 dirty_background_bytes=0
> [ 466.322618] vm direct limit must be set greater than background limit. bg_thresh=0 thresh=0 bg_bytes=0 bytes=0 bg_ratio=409 ratio=1228 gdtc= (null) gdtc->vail=0 vm_dirty_bytes=0 dirty_background_bytes=0
> [ 466.497893] vm direct limit must be set greater than background limit. bg_thresh=0 thresh=0 bg_bytes=0 bytes=0 bg_ratio=409 ratio=1228 gdtc= (null) gdtc->vail=0 vm_dirty_bytes=0 dirty_background_bytes=0
> [ 466.504687] vm direct limit must be set greater than background limit. bg_thresh=0 thresh=0 bg_bytes=0 bytes=0 bg_ratio=409 ratio=1228 gdtc= (null) gdtc->vail=0 vm_dirty_bytes=0 dirty_background_bytes=0
Hi Tetsuo,
Bellow is the code analysis,
// global_dirtyable_memory() will return number of globally dirtyable page
gdtc.avail = global_dirtyable_memory();
domain_dirty_limits(&gdtc);
unsigned long ratio = (vm_dirty_ratio * PAGE_SIZE) / 100; // 1228
unsigned long bg_ratio = (dirty_background_ratio * PAGE_SIZE)
/ 100; // 409
available_memory = dtc->avail;
thresh = (ratio * available_memory) / PAGE_SIZE;
bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE;
So if available_memory is less than 4 pages, thresh and bg_thresh will
be both 0,
then the message will be printed.
Thanks
Yafang
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