docs/vm: highmem.txt: convert to ReST format

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

Documentation/vm/highmem.txt

+.. _highmem:
 
-			     ====================
-			     HIGH MEMORY HANDLING
-			     ====================
+====================
+High Memory Handling
+====================
 
 By: Peter Zijlstra <a.p.zijlstra@chello.nl>
 
-Contents:
-
- (*) What is high memory?
-
- (*) Temporary virtual mappings.
-
- (*) Using kmap_atomic.
-
- (*) Cost of temporary mappings.
-
- (*) i386 PAE.
+.. contents:: :local:
 
-
-====================
-WHAT IS HIGH MEMORY?
+What Is High Memory?
 ====================
 
 High memory (highmem) is used when the size of physical memory approaches or
@@ -38,7 +27,7 @@ kernel entry/exit.  This means the available virtual memory space (4GiB on
 i386) has to be divided between user and kernel space.
 
 The traditional split for architectures using this approach is 3:1, 3GiB for
-userspace and the top 1GiB for kernel space:
+userspace and the top 1GiB for kernel space::
 
 		+--------+ 0xffffffff
 		| Kernel |
@@ -58,22 +47,21 @@ and user maps.  Some hardware (like some ARMs), however, have limited virtual
 space when they use mm context tags.
 
 
-==========================
-TEMPORARY VIRTUAL MAPPINGS
+Temporary Virtual Mappings
 ==========================
 
 The kernel contains several ways of creating temporary mappings:
 
- (*) vmap().  This can be used to make a long duration mapping of multiple
+* vmap().  This can be used to make a long duration mapping of multiple
   physical pages into a contiguous virtual space.  It needs global
   synchronization to unmap.
 
- (*) kmap().  This permits a short duration mapping of a single page.  It needs
+* kmap().  This permits a short duration mapping of a single page.  It needs
   global synchronization, but is amortized somewhat.  It is also prone to
   deadlocks when using in a nested fashion, and so it is not recommended for
   new code.
 
- (*) kmap_atomic().  This permits a very short duration mapping of a single
+* kmap_atomic().  This permits a very short duration mapping of a single
   page.  Since the mapping is restricted to the CPU that issued it, it
   performs well, but the issuing task is therefore required to stay on that
   CPU until it has finished, lest some other task displace its mappings.
@@ -84,14 +72,13 @@ The kernel contains several ways of creating temporary mappings:
   It may be assumed that k[un]map_atomic() won't fail.
 
 
-=================
-USING KMAP_ATOMIC
+Using kmap_atomic
 =================
 
 When and where to use kmap_atomic() is straightforward.  It is used when code
 wants to access the contents of a page that might be allocated from high memory
 (see __GFP_HIGHMEM), for example a page in the pagecache.  The API has two
-functions, and they can be used in a manner similar to the following:
+functions, and they can be used in a manner similar to the following::
 
 	/* Find the page of interest. */
 	struct page *page = find_get_page(mapping, offset);
@@ -109,7 +96,7 @@ Note that the kunmap_atomic() call takes the result of the kmap_atomic() call
 not the argument.
 
 If you need to map two pages because you want to copy from one page to
-another you need to keep the kmap_atomic calls strictly nested, like:
+another you need to keep the kmap_atomic calls strictly nested, like::
 
 	vaddr1 = kmap_atomic(page1);
 	vaddr2 = kmap_atomic(page2);
@@ -120,8 +107,7 @@ another you need to keep the kmap_atomic calls strictly nested, like:
 	kunmap_atomic(vaddr1);
 
 
-==========================
-COST OF TEMPORARY MAPPINGS
+Cost of Temporary Mappings
 ==========================
 
 The cost of creating temporary mappings can be quite high.  The arch has to
@@ -136,22 +122,21 @@ If CONFIG_MMU is not set, then there can be no temporary mappings and no
 highmem.  In such a case, the arithmetic approach will also be used.
 
 
-========
 i386 PAE
 ========
 
 The i386 arch, under some circumstances, will permit you to stick up to 64GiB
 of RAM into your 32-bit machine.  This has a number of consequences:
 
- (*) Linux needs a page-frame structure for each page in the system and the
+* Linux needs a page-frame structure for each page in the system and the
   pageframes need to live in the permanent mapping, which means:
 
- (*) you can have 896M/sizeof(struct page) page-frames at most; with struct
+* you can have 896M/sizeof(struct page) page-frames at most; with struct
   page being 32-bytes that would end up being something in the order of 112G
   worth of pages; the kernel, however, needs to store more than just
   page-frames in that memory...
 
- (*) PAE makes your page tables larger - which slows the system down as more
+* PAE makes your page tables larger - which slows the system down as more
   data has to be accessed to traverse in TLB fills and the like.  One
   advantage is that PAE has more PTE bits and can provide advanced features
   like NX and PAT.