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

[Andrew Morton]

On Tue, 17 Mar 2026 08:33:55 -0700 Breno Leitao <leitao@xxxxxxxxxx> 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@xxxxxxxxxx

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;
_