Re: [PATCH v7 0/4] mm: thp: reduce unnecessary start_stop_khugepaged() calls

Andrew Morton
2026-03-17T16:52:19Z

On Tue, 17 Mar 2026 08:33:55 -0700 Breno Leitao <leitao@debian.org> 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 easier to digest and
> ratelimiting the message.
>
> This version is heavily based on Lorenzo's suggestion on V1.
>
> ---
> Changes in v7:
> - Keep the atomic test_and_set_bit() in set_global_enabled_mode (Sohil)
> - Link to v6: https://patch.msgid.link/20260311-thp_logs-v6-0-421e30d881e0@debian.org

Thanks, I updated mm.git's mm-unstable branch.

Below is how v7 altered mm.git:

--- a/mm/huge_memory.c~b
+++ a/mm/huge_memory.c
@@ -353,11 +353,11 @@ static bool set_global_enabled_mode(enum

for (m = 0; m < ARRAY_SIZE(thp_flags); m++) {
if (m == mode)
- changed |= !__test_and_set_bit(thp_flags[m],
- &transparent_hugepage_flags);
+ changed |= !test_and_set_bit(thp_flags[m],
+ &transparent_hugepage_flags);
else
- changed |= __test_and_clear_bit(thp_flags[m],
- &transparent_hugepage_flags);
+ changed |= test_and_clear_bit(thp_flags[m],
+ &transparent_hugepage_flags);
}

return changed;
_