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>

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.
 

mm/page_alloc.c

@@ -273,7 +273,9 @@ static unsigned long __meminitdata dma_reserve;
 static unsigned long __meminitdata arch_zone_lowest_possible_pfn[MAX_NR_ZONES];
 static unsigned long __meminitdata arch_zone_highest_possible_pfn[MAX_NR_ZONES];
 static unsigned long __initdata required_kernelcore;
+static unsigned long required_kernelcore_percent __initdata;
 static unsigned long __initdata required_movablecore;
+static unsigned long required_movablecore_percent __initdata;
 static unsigned long __meminitdata zone_movable_pfn[MAX_NUMNODES];
 static bool mirrored_kernelcore;
 
@@ -6571,7 +6573,18 @@ static void __init find_zone_movable_pfns_for_nodes(void)
 	}
 
 	/*
-	 * If movablecore=nn[KMG] was specified, calculate what size of
+	 * If kernelcore=nn% or movablecore=nn% was specified, calculate the
+	 * amount of necessary memory.
+	 */
+	if (required_kernelcore_percent)
+		required_kernelcore = (totalpages * 100 * required_kernelcore_percent) /
+				       10000UL;
+	if (required_movablecore_percent)
+		required_movablecore = (totalpages * 100 * required_movablecore_percent) /
+					10000UL;
+
+	/*
+	 * If movablecore= was specified, calculate what size of
 	 * kernelcore that corresponds so that memory usable for
 	 * any allocation type is evenly spread. If both kernelcore
 	 * and movablecore are specified, then the value of kernelcore
@@ -6811,18 +6824,30 @@ void __init free_area_init_nodes(unsigned long *max_zone_pfn)
 	zero_resv_unavail();
 }
 
-static int __init cmdline_parse_core(char *p, unsigned long *core)
+static int __init cmdline_parse_core(char *p, unsigned long *core,
+				     unsigned long *percent)
 {
 	unsigned long long coremem;
+	char *endptr;
+
 	if (!p)
 		return -EINVAL;
 
-	coremem = memparse(p, &p);
-	*core = coremem >> PAGE_SHIFT;
+	/* Value may be a percentage of total memory, otherwise bytes */
+	coremem = simple_strtoull(p, &endptr, 0);
+	if (*endptr == '%') {
+		/* Paranoid check for percent values greater than 100 */
+		WARN_ON(coremem > 100);
 
+		*percent = coremem;
+	} else {
+		coremem = memparse(p, &p);
 		/* Paranoid check that UL is enough for the coremem value */
 		WARN_ON((coremem >> PAGE_SHIFT) > ULONG_MAX);
 
+		*core = coremem >> PAGE_SHIFT;
+		*percent = 0UL;
+	}
 	return 0;
 }
 
@@ -6838,7 +6863,8 @@ static int __init cmdline_parse_kernelcore(char *p)
 		return 0;
 	}
 
-	return cmdline_parse_core(p, &required_kernelcore);
+	return cmdline_parse_core(p, &required_kernelcore,
+				  &required_kernelcore_percent);
 }
 
 /*
@@ -6847,7 +6873,8 @@ static int __init cmdline_parse_kernelcore(char *p)
  */
 static int __init cmdline_parse_movablecore(char *p)
 {
-	return cmdline_parse_core(p, &required_movablecore);
+	return cmdline_parse_core(p, &required_movablecore,
+				  &required_movablecore_percent);
 }
 
 early_param("kernelcore", cmdline_parse_kernelcore);