Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
---
Documentation/vm/split_page_table_lock | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/Documentation/vm/split_page_table_lock b/Documentation/vm/split_page_table_lock
index 62842a8..889b00b 100644
--- a/Documentation/vm/split_page_table_lock
+++ b/Documentation/vm/split_page_table_lock
@@ -1,3 +1,6 @@
+.. _split_page_table_lock:
+
+=====================
Split page table lock
=====================
@@ -11,6 +14,7 @@ access to the table. At the moment we use split lock for PTE and PMD
tables. Access to higher level tables protected by mm->page_table_lock.
There are helpers to lock/unlock a table and other accessor functions:
+
- pte_offset_map_lock()
maps pte and takes PTE table lock, returns pointer to the taken
lock;
@@ -34,12 +38,13 @@ Split page table lock for PMD tables is enabled, if it's enabled for PTE
tables and the architecture supports it (see below).
Hugetlb and split page table lock
----------------------------------
+=================================
Hugetlb can support several page sizes. We use split lock only for PMD
level, but not for PUD.
Hugetlb-specific helpers:
+
- huge_pte_lock()
takes pmd split lock for PMD_SIZE page, mm->page_table_lock
otherwise;
@@ -47,7 +52,7 @@ Hugetlb-specific helpers:
returns pointer to table lock;
Support of split page table lock by an architecture
----------------------------------------------------
+===================================================
There's no need in special enabling of PTE split page table lock:
everything required is done by pgtable_page_ctor() and pgtable_page_dtor(),
@@ -73,7 +78,7 @@ NOTE: pgtable_page_ctor() and pgtable_pmd_page_ctor() can fail -- it must
be handled properly.
page->ptl
----------
+=========
page->ptl is used to access split page table lock, where 'page' is struct
page of page containing the table. It shares storage with page->private
@@ -81,6 +86,7 @@ page of page containing the table. It shares storage with page->private
To avoid increasing size of struct page and have best performance, we use a
trick:
+
- if spinlock_t fits into long, we use page->ptr as spinlock, so we
can avoid indirect access and save a cache line.
- if size of spinlock_t is bigger then size of long, we use page->ptl as
--
2.7.4
