percpu: generalize first chunk allocator selection

Now that all first chunk allocators are in mm/percpu.c, it makes sense
to make generalize percpu_alloc kernel parameter.  Define PCPU_FC_*
and set pcpu_chosen_fc using early_param() in mm/percpu.c.  Arch code
can use the set value to determine which first chunk allocator to use.
Signed-off-by: Tejun Heo <tj@kernel.org>

Documentation/kernel-parameters.txt

@@ -1919,11 +1919,12 @@ and is between 256 and 4096 characters. It is defined in the file
 			Format: { 0 | 1 }
 			See arch/parisc/kernel/pdc_chassis.c
 
-	percpu_alloc=	[X86] Select which percpu first chunk allocator to use.
-			Allowed values are one of "lpage", "embed" and "page".
-			See comments in arch/x86/kernel/setup_percpu.c for
-			details on each allocator.  This parameter is primarily
-			for debugging and performance comparison.
+	percpu_alloc=	Select which percpu first chunk allocator to use.
+			Currently supported values are "embed", "page" and
+			"lpage".  Archs may support subset or none of the
+			selections.  See comments in mm/percpu.c for details
+			on each allocator.  This parameter is primarily	for
+			debugging and performance comparison.
 
 	pf.		[PARIDE]
 			See Documentation/blockdev/paride.txt.

arch/x86/kernel/setup_percpu.c

@@ -267,16 +267,6 @@ static ssize_t __init setup_pcpu_page(size_t static_size)
 				     pcpup_populate_pte);
 }
 
-/* for explicit first chunk allocator selection */
-static char pcpu_chosen_alloc[16] __initdata;
-
-static int __init percpu_alloc_setup(char *str)
-{
-	strncpy(pcpu_chosen_alloc, str, sizeof(pcpu_chosen_alloc) - 1);
-	return 0;
-}
-early_param("percpu_alloc", percpu_alloc_setup);
-
 static inline void setup_percpu_segment(int cpu)
 {
 #ifdef CONFIG_X86_32
@@ -307,19 +297,17 @@ void __init setup_per_cpu_areas(void)
 	 * each allocator for details.
 	 */
 	ret = -EINVAL;
-	if (strlen(pcpu_chosen_alloc)) {
-		if (strcmp(pcpu_chosen_alloc, "page")) {
-			if (!strcmp(pcpu_chosen_alloc, "lpage"))
+	if (pcpu_chosen_fc != PCPU_FC_AUTO) {
+		if (pcpu_chosen_fc != PCPU_FC_PAGE) {
+			if (pcpu_chosen_fc == PCPU_FC_LPAGE)
 				ret = setup_pcpu_lpage(static_size, true);
-			else if (!strcmp(pcpu_chosen_alloc, "embed"))
-				ret = setup_pcpu_embed(static_size, true);
 			else
-				pr_warning("PERCPU: unknown allocator %s "
-					   "specified\n", pcpu_chosen_alloc);
+				ret = setup_pcpu_embed(static_size, true);
+
 			if (ret < 0)
 				pr_warning("PERCPU: %s allocator failed (%zd), "
 					   "falling back to page size\n",
-					   pcpu_chosen_alloc, ret);
+					   pcpu_fc_names[pcpu_chosen_fc], ret);
 		}
 	} else {
 		ret = setup_pcpu_lpage(static_size, false);

include/linux/percpu.h

@@ -59,6 +59,18 @@
 extern void *pcpu_base_addr;
 extern const int *pcpu_unit_map;
 
+enum pcpu_fc {
+	PCPU_FC_AUTO,
+	PCPU_FC_EMBED,
+	PCPU_FC_PAGE,
+	PCPU_FC_LPAGE,
+
+	PCPU_FC_NR,
+};
+extern const char *pcpu_fc_names[PCPU_FC_NR];
+
+extern enum pcpu_fc pcpu_chosen_fc;
+
 typedef void * (*pcpu_fc_alloc_fn_t)(unsigned int cpu, size_t size);
 typedef void (*pcpu_fc_free_fn_t)(void *ptr, size_t size);
 typedef void (*pcpu_fc_populate_pte_fn_t)(unsigned long addr);

mm/percpu.c

@@ -1414,6 +1414,38 @@ size_t __init pcpu_setup_first_chunk(size_t static_size, size_t reserved_size,
 	return pcpu_unit_size;
 }
 
+const char *pcpu_fc_names[PCPU_FC_NR] __initdata = {
+	[PCPU_FC_AUTO]	= "auto",
+	[PCPU_FC_EMBED]	= "embed",
+	[PCPU_FC_PAGE]	= "page",
+	[PCPU_FC_LPAGE]	= "lpage",
+};
+
+enum pcpu_fc pcpu_chosen_fc __initdata = PCPU_FC_AUTO;
+
+static int __init percpu_alloc_setup(char *str)
+{
+	if (0)
+		/* nada */;
+#ifdef CONFIG_NEED_PER_CPU_EMBED_FIRST_CHUNK
+	else if (!strcmp(str, "embed"))
+		pcpu_chosen_fc = PCPU_FC_EMBED;
+#endif
+#ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK
+	else if (!strcmp(str, "page"))
+		pcpu_chosen_fc = PCPU_FC_PAGE;
+#endif
+#ifdef CONFIG_NEED_PER_CPU_LPAGE_FIRST_CHUNK
+	else if (!strcmp(str, "lpage"))
+		pcpu_chosen_fc = PCPU_FC_LPAGE;
+#endif
+	else
+		pr_warning("PERCPU: unknown allocator %s specified\n", str);
+
+	return 0;
+}
+early_param("percpu_alloc", percpu_alloc_setup);
+
 static inline size_t pcpu_calc_fc_sizes(size_t static_size,
 					size_t reserved_size,
 					ssize_t *dyn_sizep)