Re: [PATCH v2 0/3] mm: thp: reduce unnecessary start_stop_khugepaged() calls

[Baolin Wang <baolin.wang@linux.alibaba.com>]

On 3/5/26 10:04 PM, 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 100 messages like:
> 
>        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.
> 
> For instance, at Meta's fleet, ~10K servers were producing 3.5M of
> these messages per day.
> 
> Fix this by making the sysfs _store helpers a no-op if there is no state
> change.
> 
> This version is heavily based on Lorezo's suggestion on V1.

Thanks for doing this. And you should also consider the shmem parts: 
shmem_enabled_store() and thpsize_shmem_enabled_store(), both of which 
will also call start_stop_khugepaged().

That means you can also generate lots of messages with the following script.

# for i in $(seq 100); do
#       echo 1024 > /proc/sys/vm/min_free_kbytes
#       echo always > /sys/kernel/mm/transparent_hugepage/shmem_enabled
# done


> ---
> Changes in v2:
> - V2 is heavily based on Lorenzo and Kiryl feedback on v1.
> - Link to v1: https://patch.msgid.link/20260304-thp_logs-v1-0-59038218a253@debian.org
> 
> ---
> Breno Leitao (3):
>        mm: khugepaged: export set_recommended_min_free_kbytes()
>        mm: huge_memory: refactor anon_enabled_store() with change_anon_orders()
>        mm: huge_memory: refactor enabled_store() with change_enabled()
> 
>   include/linux/khugepaged.h |   1 +
>   mm/huge_memory.c           | 135 +++++++++++++++++++++++++++++----------------
>   mm/khugepaged.c            |   2 +-
>   3 files changed, 90 insertions(+), 48 deletions(-)
> ---
> base-commit: 9dd5012f78d699f7a6051583dc53adeb401e28f0
> change-id: 20260303-thp_logs-059d6b80f6d6
> 
> Best regards,
> --
> Breno Leitao <leitao@debian.org>