[PATCH v2] docs/mm: describe current criteria for enabling split page table lock for PTE tables

[PATCH v2] docs/mm: describe current criteria for enabling split page table lock for PTE tables

[Ethan Nelson-Moore]

The mm documentation regarding split page table lock for PTE tables
refers to the CONFIG_SPLIT_PTLOCK_CPUS config option, which was
superseded by CONFIG_SPLIT_PTE_PTLOCKS in commit 394290cba966 ("mm:
turn USE_SPLIT_PTE_PTLOCKS / USE_SPLIT_PTE_PTLOCKS into Kconfig
options"). Update the documentation to refer to the current option and
document that it is not supported on some architectures.

Discovered while searching for CONFIG_* symbols referenced in the
kernel but not defined in any Kconfig file.

Signed-off-by: Ethan Nelson-Moore <enelsonmoore@gmail.com>
---
Changes in v2: Remove list of unsupported architectures for conciseness

 Documentation/mm/split_page_table_lock.rst | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/Documentation/mm/split_page_table_lock.rst b/Documentation/mm/split_page_table_lock.rst
index cc3cd46abd1b..3a35988f3c16 100644
--- a/Documentation/mm/split_page_table_lock.rst
+++ b/Documentation/mm/split_page_table_lock.rst
@@ -37,8 +37,9 @@ There are helpers to lock/unlock a table and other accessor functions:
  - pmd_lockptr()
 	returns pointer to PMD table lock;
 
-Split page table lock for PTE tables is enabled compile-time if
-CONFIG_SPLIT_PTLOCK_CPUS (usually 4) is less or equal to NR_CPUS.
+Split page table lock for PTE tables is enabled compile-time (via
+CONFIG_SPLIT_PTE_PTLOCKS) if NR_CPUS is greater than or equal to 4 and an
+MMU is being used. However, it is not supported on some architectures.
 If split lock is disabled, all tables are guarded by mm->page_table_lock.
 
 Split page table lock for PMD tables is enabled, if it's enabled for PTE
-- 
2.43.0

Re: [PATCH v2] docs/mm: describe current criteria for enabling split page table lock for PTE tables

[Matthew Wilcox]

On Mon, Jun 15, 2026 at 03:28:29PM -0700, Ethan Nelson-Moore wrote:
> -Split page table lock for PTE tables is enabled compile-time if
> -CONFIG_SPLIT_PTLOCK_CPUS (usually 4) is less or equal to NR_CPUS.
> +Split page table lock for PTE tables is enabled compile-time (via

is enabled _at_ compile time?

> +CONFIG_SPLIT_PTE_PTLOCKS) if NR_CPUS is greater than or equal to 4 and an
> +MMU is being used. However, it is not supported on some architectures.
>  If split lock is disabled, all tables are guarded by mm->page_table_lock.
>  
>  Split page table lock for PMD tables is enabled, if it's enabled for PTE
> -- 
> 2.43.0
> 
> 

Re: [PATCH v2] docs/mm: describe current criteria for enabling split page table lock for PTE tables

[Ethan Nelson-Moore]

Hi, Matthew,

On Mon, Jun 15, 2026 at 3:36 PM Matthew Wilcox <willy@infradead.org> wrote:
> is enabled _at_ compile time?

Yes, I think that would be better. This section of the documentation
has a lot of grammar errors, though, and I didn't want to spend my
time fixing them at the moment.

Ethan