Re: [PATCH 0/2] mm: thp: reduce unnecessary start_stop_khugepaged() calls

[Lorenzo Stoakes (Oracle)]

On Wed, Mar 04, 2026 at 02:22:32AM -0800, Breno Leitao wrote:
> Writing to /sys/kernel/mm/transparent_hugepage/enabled causes
> start_stop_khugepaged() called independent of any change.
> start_stop_khugepaged() SPAMs  the printk ring buffer overflow with the
> exact same message, even when nothing changes.
>
> For instance, if you have a custom vm.min_free_kbytes, just touching
> /sys/kernel/mm/transparent_hugepage/enabled causes a printk message.
> Example:
>
>       # sysctl -w vm.min_free_kbytes=112382
>       # for i in $(seq 100); do echo never > /sys/kernel/mm/transparent_hugepage/enabled ; done
>
> and you have 100 WARN messages like the following, which is pretty dull:
>
>       khugepaged: min_free_kbytes is not updated to 112381 because user defined value 112382 is preferred
>
> A similar message shows up when setting thp to "always":
>
>       # for i in $(seq 100); do
>       #       echo 1024 > /proc/sys/vm/min_free_kbytes
>       #       echo always > /sys/kernel/mm/transparent_hugepage/enabled
>       # done
>
> And then, we have 100K messages like:

You mean 100? :)

It's 100 locally here.

>
>       khugepaged: raising min_free_kbytes from 1024 to 67584 to help transparent hugepage allocations
>
> This is more common when you have a configuration management system that
> writes the THP configuration without an extra read, assuming that
> nothing will happen if there is no change in the configuration, but it
> prints these annoying messages.

Right.

>
> For instance, at Meta's fleet, ~10K servers were producing 3.5M of
> these messages per day.

Yeah... that's not so fun :)

>
> Fix this by doing two things:
>  * Make the sysfs _store helpers a no-op if there is no state change
>  * Ratelimit these messages to avoid SPAM on config change

Thanks for taking a look at this!

>
> ---
> Breno Leitao (2):
>       mm: thp: avoid calling start_stop_khugepaged() in anon_enabled_store()
>       mm: thp: avoid calling start_stop_khugepaged() in enabled_store()
>
>  mm/huge_memory.c | 48 ++++++++++++++++++++++++++++--------------------
>  1 file changed, 28 insertions(+), 20 deletions(-)
> ---
> base-commit: 9dd5012f78d699f7a6051583dc53adeb401e28f0
> change-id: 20260303-thp_logs-059d6b80f6d6
>
> Best regards,
> --
> Breno Leitao <leitao@xxxxxxxxxx>
>

Cheers, Lorenzo