mm/Kconfig: update "Memory Model" help text

The help describing the memory model selection is outdated.  It still says
that SPARSEMEM is experimental and DISCONTIGMEM is a preferred over
SPARSEMEM.

Update the help text for the relevant options:
* add a generic help for the "Memory Model" prompt
* add description for FLATMEM
* reduce the description of DISCONTIGMEM and add a deprecation note
* prefer SPARSEMEM over DISCONTIGMEM

Link: http://lkml.kernel.org/r/1556188531-20728-1-git-send-email-rppt@linux.ibm.com
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/Kconfig

@@ -11,23 +11,24 @@ choice
 	default DISCONTIGMEM_MANUAL if ARCH_DISCONTIGMEM_DEFAULT
 	default SPARSEMEM_MANUAL if ARCH_SPARSEMEM_DEFAULT
 	default FLATMEM_MANUAL
+	help
+	  This option allows you to change some of the ways that
+	  Linux manages its memory internally. Most users will
+	  only have one option here selected by the architecture
+	  configuration. This is normal.
 
 config FLATMEM_MANUAL
 	bool "Flat Memory"
 	depends on !(ARCH_DISCONTIGMEM_ENABLE || ARCH_SPARSEMEM_ENABLE) || ARCH_FLATMEM_ENABLE
 	help
-	  This option allows you to change some of the ways that
+	  This option is best suited for non-NUMA systems with
-	  Linux manages its memory internally.  Most users will
+	  flat address space. The FLATMEM is the most efficient
-	  only have one option here: FLATMEM.  This is normal
+	  system in terms of performance and resource consumption
-	  and a correct option.
+	  and it is the best option for smaller systems.
 
-	  Some users of more advanced features like NUMA and
+	  For systems that have holes in their physical address
-	  memory hotplug may have different options here.
+	  spaces and for features like NUMA and memory hotplug,
-	  DISCONTIGMEM is a more mature, better tested system,
+	  choose "Sparse Memory"
-	  but is incompatible with memory hotplug and may suffer
-	  decreased performance over SPARSEMEM.  If unsure between
-	  "Sparse Memory" and "Discontiguous Memory", choose
-	  "Discontiguous Memory".
 
 	  If unsure, choose this option (Flat Memory) over any other.
 
@@ -38,29 +39,26 @@ config DISCONTIGMEM_MANUAL
 	  This option provides enhanced support for discontiguous
 	  memory systems, over FLATMEM.  These systems have holes
 	  in their physical address spaces, and this option provides
-	  more efficient handling of these holes.  However, the vast
+	  more efficient handling of these holes.
-	  majority of hardware has quite flat address spaces, and
-	  can have degraded performance from the extra overhead that
-	  this option imposes.
 
-	  Many NUMA configurations will have this as the only option.
+	  Although "Discontiguous Memory" is still used by several
+	  architectures, it is considered deprecated in favor of
+	  "Sparse Memory".
 
-	  If unsure, choose "Flat Memory" over this option.
+	  If unsure, choose "Sparse Memory" over this option.
 
 config SPARSEMEM_MANUAL
 	bool "Sparse Memory"
 	depends on ARCH_SPARSEMEM_ENABLE
 	help
 	  This will be the only option for some systems, including
-	  memory hotplug systems.  This is normal.
+	  memory hot-plug systems.  This is normal.
 
-	  For many other systems, this will be an alternative to
+	  This option provides efficient support for systems with
-	  "Discontiguous Memory".  This option provides some potential
+	  holes is their physical address space and allows memory
-	  performance benefits, along with decreased code complexity,
+	  hot-plug and hot-remove.
-	  but it is newer, and more experimental.
 
-	  If unsure, choose "Discontiguous Memory" or "Flat Memory"
+	  If unsure, choose "Flat Memory" over this option.
-	  over this option.
 
 endchoice