docs/vm: split_page_table_lock: convert to ReST format

Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/vm/split_page_table_lock

+.. _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