mm, page_alloc: extend kernelcore and movablecore for percent

Both kernelcore= and movablecore= can be used to define the amount of
ZONE_NORMAL and ZONE_MOVABLE on a system, respectively.  This requires
the system memory capacity to be known when specifying the command line,
however.

This introduces the ability to define both kernelcore= and movablecore=
as a percentage of total system memory.  This is convenient for systems
software that wants to define the amount of ZONE_MOVABLE, for example,
as a proportion of a system's memory rather than a hardcoded byte value.

To define the percentage, the final character of the parameter should be
a '%'.

mhocko: "why is anyone using these options nowadays?"

rientjes:
:
: Fragmentation of non-__GFP_MOVABLE pages due to low on memory
: situations can pollute most pageblocks on the system, as much as 1GB of
: slab being fragmented over 128GB of memory, for example.  When the
: amount of kernel memory is well bounded for certain systems, it is
: better to aggressively reclaim from existing MIGRATE_UNMOVABLE
: pageblocks rather than eagerly fallback to others.
:
: We have additional patches that help with this fragmentation if you're
: interested, specifically kcompactd compaction of MIGRATE_UNMOVABLE
: pageblocks triggered by fallback of non-__GFP_MOVABLE allocations and
: draining of pcp lists back to the zone free area to prevent stranding.

[rientjes@google.com: updates]
  Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1802131700160.71590@chino.kir.corp.google.com
Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1802121622470.179479@chino.kir.corp.google.com
Signed-off-by: David Rientjes <rientjes@google.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 27 insertions, 27 deletions

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 5ffe4c4121bd..7993021a1f6e 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1840,30 +1840,29 @@
 	keepinitrd	[HW,ARM]
 
 	kernelcore=	[KNL,X86,IA-64,PPC]
-			Format: nn[KMGTPE] | "mirror"
-			This parameter
-			specifies the amount of memory usable by the kernel
-			for non-movable allocations.  The requested amount is
-			spread evenly throughout all nodes in the system. The
-			remaining memory in each node is used for Movable
-			pages. In the event, a node is too small to have both
-			kernelcore and Movable pages, kernelcore pages will
-			take priority and other nodes will have a larger number
-			of Movable pages.  The Movable zone is used for the
-			allocation of pages that may be reclaimed or moved
-			by the page migration subsystem.  This means that
-			HugeTLB pages may not be allocated from this zone.
-			Note that allocations like PTEs-from-HighMem still
-			use the HighMem zone if it exists, and the Normal
+			Format: nn[KMGTPE] | nn% | "mirror"
+			This parameter specifies the amount of memory usable by
+			the kernel for non-movable allocations.  The requested
+			amount is spread evenly throughout all nodes in the
+			system as ZONE_NORMAL.  The remaining memory is used for
+			movable memory in its own zone, ZONE_MOVABLE.  In the
+			event, a node is too small to have both ZONE_NORMAL and
+			ZONE_MOVABLE, kernelcore memory will take priority and
+			other nodes will have a larger ZONE_MOVABLE.
+
+			ZONE_MOVABLE is used for the allocation of pages that
+			may be reclaimed or moved by the page migration
+			subsystem.  Note that allocations like PTEs-from-HighMem
+			still use the HighMem zone if it exists, and the Normal
 			zone if it does not.
 
-			Instead of specifying the amount of memory (nn[KMGTPE]),
-			you can specify "mirror" option. In case "mirror"
+			It is possible to specify the exact amount of memory in
+			the form of "nn[KMGTPE]", a percentage of total system
+			memory in the form of "nn%", or "mirror".  If "mirror"
 			option is specified, mirrored (reliable) memory is used
 			for non-movable allocations and remaining memory is used
-			for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
-			so you can NOT specify nn[KMGTPE] and "mirror" at the same
-			time.
+			for Movable pages.  "nn[KMGTPE]", "nn%", and "mirror"
+			are exclusive, so you cannot specify multiple forms.
 
 	kgdbdbgp=	[KGDB,HW] kgdb over EHCI usb debug port.
 			Format: <Controller#>[,poll interval]
@@ -2377,13 +2376,14 @@
 	mousedev.yres=	[MOUSE] Vertical screen resolution, used for devices
 			reporting absolute coordinates, such as tablets
 
-	movablecore=nn[KMG]	[KNL,X86,IA-64,PPC] This parameter
-			is similar to kernelcore except it specifies the
-			amount of memory used for migratable allocations.
-			If both kernelcore and movablecore is specified,
-			then kernelcore will be at *least* the specified
-			value but may be more. If movablecore on its own
-			is specified, the administrator must be careful
+	movablecore=	[KNL,X86,IA-64,PPC]
+			Format: nn[KMGTPE] | nn%
+			This parameter is the complement to kernelcore=, it
+			specifies the amount of memory used for migratable
+			allocations.  If both kernelcore and movablecore is
+			specified, then kernelcore will be at *least* the
+			specified value but may be more.  If movablecore on its
+			own is specified, the administrator must be careful
 			that the amount of memory usable for all allocations
 			is not too small.