* [PATCH RFC] mm: Use pr_warn_once() for min_free_kbytes warning
@ 2025-08-28 3:06 Weilin Tong
2025-08-28 6:45 ` Michal Hocko
0 siblings, 1 reply; 6+ messages in thread
From: Weilin Tong @ 2025-08-28 3:06 UTC (permalink / raw)
To: akpm, linux-mm
Cc: vbabka, surenb, mhocko, jackmanb, hannes, ziy, linux-kernel,
baolin.wang, tongweilin
When min_free_kbytes is user-configured, increasing system memory via memory
hotplug may trigger multiple recalculations of min_free_kbytes. This results
in excessive warning messages flooding the kernel log if several memory blocks
are added in a short period.
Sample dmesg output before optimization:
...
[ 1303.897214] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
[ 1303.960498] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
[ 1303.970116] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
[ 1303.979709] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
[ 1303.989254] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
[ 1303.999122] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
[ 1304.008644] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
[ 1304.018537] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
[ 1304.028054] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
[ 1304.037615] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
...
Replace pr_warn() with pr_warn_once() to ensure only one warning is printed,
preventing large volumes of repeated log entries and improving log readability.
Signed-off-by: Weilin Tong <tongweilin@linux.alibaba.com>
---
mm/page_alloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index baead29b3e67..774723150e5b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6412,7 +6412,7 @@ void calculate_min_free_kbytes(void)
if (new_min_free_kbytes > user_min_free_kbytes)
min_free_kbytes = clamp(new_min_free_kbytes, 128, 262144);
else
- pr_warn("min_free_kbytes is not updated to %d because user defined value %d is preferred\n",
+ pr_warn_once("min_free_kbytes is not updated to %d because user defined value %d is preferred\n",
new_min_free_kbytes, user_min_free_kbytes);
}
--
2.43.7
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [PATCH RFC] mm: Use pr_warn_once() for min_free_kbytes warning
2025-08-28 3:06 [PATCH RFC] mm: Use pr_warn_once() for min_free_kbytes warning Weilin Tong
@ 2025-08-28 6:45 ` Michal Hocko
2025-08-28 9:23 ` Weilin Tong
0 siblings, 1 reply; 6+ messages in thread
From: Michal Hocko @ 2025-08-28 6:45 UTC (permalink / raw)
To: Weilin Tong
Cc: akpm, linux-mm, vbabka, surenb, jackmanb, hannes, ziy,
linux-kernel, baolin.wang
On Thu 28-08-25 11:06:02, Weilin Tong wrote:
> When min_free_kbytes is user-configured, increasing system memory via memory
> hotplug may trigger multiple recalculations of min_free_kbytes. This results
> in excessive warning messages flooding the kernel log if several memory blocks
> are added in a short period.
>
> Sample dmesg output before optimization:
> ...
> [ 1303.897214] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> [ 1303.960498] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> [ 1303.970116] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> [ 1303.979709] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> [ 1303.989254] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> [ 1303.999122] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> [ 1304.008644] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> [ 1304.018537] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> [ 1304.028054] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> [ 1304.037615] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> ...
>
> Replace pr_warn() with pr_warn_once() to ensure only one warning is printed,
> preventing large volumes of repeated log entries and improving log readability.
pr_warn_once seems too aggressive as we could miss useful events. On the
other hand I agree that repeating the same message for each memory block
onlining is not really helpful. Would it make sense to only pr_warn when
new_min_free_kbytes differs from the previous one we have warned for?
>
> Signed-off-by: Weilin Tong <tongweilin@linux.alibaba.com>
> ---
> mm/page_alloc.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index baead29b3e67..774723150e5b 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6412,7 +6412,7 @@ void calculate_min_free_kbytes(void)
> if (new_min_free_kbytes > user_min_free_kbytes)
> min_free_kbytes = clamp(new_min_free_kbytes, 128, 262144);
> else
> - pr_warn("min_free_kbytes is not updated to %d because user defined value %d is preferred\n",
> + pr_warn_once("min_free_kbytes is not updated to %d because user defined value %d is preferred\n",
> new_min_free_kbytes, user_min_free_kbytes);
>
> }
> --
> 2.43.7
--
Michal Hocko
SUSE Labs
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH RFC] mm: Use pr_warn_once() for min_free_kbytes warning
2025-08-28 6:45 ` Michal Hocko
@ 2025-08-28 9:23 ` Weilin Tong
2025-08-28 9:40 ` Michal Hocko
0 siblings, 1 reply; 6+ messages in thread
From: Weilin Tong @ 2025-08-28 9:23 UTC (permalink / raw)
To: Michal Hocko
Cc: akpm, linux-mm, vbabka, surenb, jackmanb, hannes, ziy,
linux-kernel, baolin.wang
在 2025/8/28 14:45, Michal Hocko 写道:
> On Thu 28-08-25 11:06:02, Weilin Tong wrote:
>> When min_free_kbytes is user-configured, increasing system memory via memory
>> hotplug may trigger multiple recalculations of min_free_kbytes. This results
>> in excessive warning messages flooding the kernel log if several memory blocks
>> are added in a short period.
>>
>> Sample dmesg output before optimization:
>> ...
>> [ 1303.897214] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
>> [ 1303.960498] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
>> [ 1303.970116] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
>> [ 1303.979709] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
>> [ 1303.989254] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
>> [ 1303.999122] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
>> [ 1304.008644] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
>> [ 1304.018537] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
>> [ 1304.028054] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
>> [ 1304.037615] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
>> ...
>>
>> Replace pr_warn() with pr_warn_once() to ensure only one warning is printed,
>> preventing large volumes of repeated log entries and improving log readability.
> pr_warn_once seems too aggressive as we could miss useful events. On the
> other hand I agree that repeating the same message for each memory block
> onlining is not really helpful. Would it make sense to only pr_warn when
> new_min_free_kbytes differs from the previous one we have warned for?
Thanks for your feedback!
The dmesg output above comes from hotplugging a large amount of memory
into ZONE_MOVABLE, where new_min_free_kbytes does not actually change,
resulting in repeated warnings with identical messages.
However, if memory is hotplugged into ZONE_NORMAL (such as pmem-type
memory), new_min_free_kbytes changes on each operation, so we still get
a large number of warnings—even though the value is different each time.
If the concern is missing useful warnings, pr_warn_ratelimited() would
be an acceptable alternative, as it can reduce log spam without
completely suppressing potentially important messages. However I still
think that printing the warning once is sufficient to alert the user
about the overridden configuration, especially since this is not a
particularly critical warning.
>> Signed-off-by: Weilin Tong <tongweilin@linux.alibaba.com>
>> ---
>> mm/page_alloc.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index baead29b3e67..774723150e5b 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -6412,7 +6412,7 @@ void calculate_min_free_kbytes(void)
>> if (new_min_free_kbytes > user_min_free_kbytes)
>> min_free_kbytes = clamp(new_min_free_kbytes, 128, 262144);
>> else
>> - pr_warn("min_free_kbytes is not updated to %d because user defined value %d is preferred\n",
>> + pr_warn_once("min_free_kbytes is not updated to %d because user defined value %d is preferred\n",
>> new_min_free_kbytes, user_min_free_kbytes);
>>
>> }
>> --
>> 2.43.7
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH RFC] mm: Use pr_warn_once() for min_free_kbytes warning
2025-08-28 9:23 ` Weilin Tong
@ 2025-08-28 9:40 ` Michal Hocko
[not found] ` <9639adfe-13ba-4c27-8ba6-8bf3e2190450@linux.alibaba.com>
0 siblings, 1 reply; 6+ messages in thread
From: Michal Hocko @ 2025-08-28 9:40 UTC (permalink / raw)
To: Weilin Tong
Cc: akpm, linux-mm, vbabka, surenb, jackmanb, hannes, ziy,
linux-kernel, baolin.wang
On Thu 28-08-25 17:23:40, Weilin Tong wrote:
> 在 2025/8/28 14:45, Michal Hocko 写道:
>
> > On Thu 28-08-25 11:06:02, Weilin Tong wrote:
> > > When min_free_kbytes is user-configured, increasing system memory via memory
> > > hotplug may trigger multiple recalculations of min_free_kbytes. This results
> > > in excessive warning messages flooding the kernel log if several memory blocks
> > > are added in a short period.
> > >
> > > Sample dmesg output before optimization:
> > > ...
> > > [ 1303.897214] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> > > [ 1303.960498] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> > > [ 1303.970116] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> > > [ 1303.979709] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> > > [ 1303.989254] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> > > [ 1303.999122] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> > > [ 1304.008644] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> > > [ 1304.018537] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> > > [ 1304.028054] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> > > [ 1304.037615] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> > > ...
> > >
> > > Replace pr_warn() with pr_warn_once() to ensure only one warning is printed,
> > > preventing large volumes of repeated log entries and improving log readability.
> > pr_warn_once seems too aggressive as we could miss useful events. On the
> > other hand I agree that repeating the same message for each memory block
> > onlining is not really helpful. Would it make sense to only pr_warn when
> > new_min_free_kbytes differs from the previous one we have warned for?
> Thanks for your feedback!
>
> The dmesg output above comes from hotplugging a large amount of memory into
> ZONE_MOVABLE, where new_min_free_kbytes does not actually change, resulting
> in repeated warnings with identical messages.
Yes, this is clear from the changelog
> However, if memory is hotplugged into ZONE_NORMAL (such as pmem-type
> memory), new_min_free_kbytes changes on each operation, so we still get a
> large number of warnings—even though the value is different each time.
We can check whether the value has changed considerably.
> If the concern is missing useful warnings, pr_warn_ratelimited() would be an
> acceptable alternative, as it can reduce log spam without completely
> suppressing potentially important messages. However I still think that
> printing the warning once is sufficient to alert the user about the
> overridden configuration, especially since this is not a particularly
> critical warning.
The thing is that kernel log buffer can easily overflow and you can lose
those messages over time, especially for system with a large uptime -
which is far from uncommon.
I am not entirely enthusiastic about rate limiting because that is time
rather than even driven. Anyway, if you can make ratelimiting work for
your usecase, then no objection from me but I would rather make the
reporting more useful than hack around it.
--
Michal Hocko
SUSE Labs
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2025-08-28 10:30 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
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2025-08-28 3:06 [PATCH RFC] mm: Use pr_warn_once() for min_free_kbytes warning Weilin Tong
2025-08-28 6:45 ` Michal Hocko
2025-08-28 9:23 ` Weilin Tong
2025-08-28 9:40 ` Michal Hocko
[not found] ` <9639adfe-13ba-4c27-8ba6-8bf3e2190450@linux.alibaba.com>
2025-08-28 10:09 ` Michal Hocko
2025-08-28 10:30 ` Weilin Tong
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