x86: do not PSE on CONFIG_DEBUG_PAGEALLOC=y

get more testing of the c_p_a() code done by not turning off
PSE on DEBUG_PAGEALLOC.

this simplifies the early pagetable setup code, and tests
the largepage-splitup code quite heavily.

In the end, all the largepages will be split up pretty quickly,
so there's no difference to how DEBUG_PAGEALLOC worked before.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/cpu/common.c

@@ -641,13 +641,6 @@ void __init early_cpu_init(void)
 	nexgen_init_cpu();
 	umc_init_cpu();
 	early_cpu_detect();
-
-#ifdef CONFIG_DEBUG_PAGEALLOC
-	/* pse is not compatible with on-the-fly unmapping,
-	 * disable it even if the cpus claim to support it.
-	 */
-	setup_clear_cpu_cap(X86_FEATURE_PSE);
-#endif
 }
 
 /* Make sure %fs is initialized properly in idle threads */

arch/x86/mm/pageattr_32.c

@@ -61,13 +61,17 @@ static void __set_pmd_pte(pte_t *kpte, unsigned long address, pte_t pte)
 static int split_large_page(pte_t *kpte, unsigned long address)
 {
 	pgprot_t ref_prot = pte_pgprot(pte_clrhuge(*kpte));
+	gfp_t gfp_flags = GFP_KERNEL;
 	unsigned long flags;
 	unsigned long addr;
 	pte_t *pbase, *tmp;
 	struct page *base;
 	int i, level;
 
-	base = alloc_pages(GFP_KERNEL, 0);
+#ifdef CONFIG_DEBUG_PAGEALLOC
+	gfp_flags = GFP_ATOMIC;
+#endif
+	base = alloc_pages(gfp_flags, 0);
 	if (!base)
 		return -ENOMEM;
 
@@ -218,6 +222,12 @@ void kernel_map_pages(struct page *page, int numpages, int enable)
 					   numpages * PAGE_SIZE);
 	}
 
+	/*
+	 * If page allocator is not up yet then do not call c_p_a():
+	 */
+	if (!debug_pagealloc_enabled)
+		return;
+
 	/*
 	 * the return value is ignored - the calls cannot fail,
 	 * large pages are disabled at boot time.

include/asm-x86/cacheflush.h

@@ -29,11 +29,6 @@ int change_page_attr(struct page *page, int numpages, pgprot_t prot);
 int change_page_attr_addr(unsigned long addr, int numpages, pgprot_t prot);
 void clflush_cache_range(void *addr, int size);
 
-#ifdef CONFIG_DEBUG_PAGEALLOC
-/* internal debugging function */
-void kernel_map_pages(struct page *page, int numpages, int enable);
-#endif
-
 #ifdef CONFIG_DEBUG_RODATA
 void mark_rodata_ro(void);
 #endif

include/linux/mm.h

@@ -1118,9 +1118,21 @@ static inline void vm_stat_account(struct mm_struct *mm,
 }
 #endif /* CONFIG_PROC_FS */
 
-#ifndef CONFIG_DEBUG_PAGEALLOC
+#ifdef CONFIG_DEBUG_PAGEALLOC
+extern int debug_pagealloc_enabled;
+
+extern void kernel_map_pages(struct page *page, int numpages, int enable);
+
+static inline void enable_debug_pagealloc(void)
+{
+	debug_pagealloc_enabled = 1;
+}
+#else
 static inline void
 kernel_map_pages(struct page *page, int numpages, int enable) {}
+static inline void enable_debug_pagealloc(void)
+{
+}
 #endif
 
 extern struct vm_area_struct *get_gate_vma(struct task_struct *tsk);

init/main.c

@@ -318,6 +318,10 @@ static int __init unknown_bootoption(char *param, char *val)
 	return 0;
 }
 
+#ifdef CONFIG_DEBUG_PAGEALLOC
+int __read_mostly debug_pagealloc_enabled = 0;
+#endif
+
 static int __init init_setup(char *str)
 {
 	unsigned int i;
@@ -552,6 +556,7 @@ asmlinkage void __init start_kernel(void)
 	preempt_disable();
 	build_all_zonelists();
 	page_alloc_init();
+	enable_debug_pagealloc();
 	printk(KERN_NOTICE "Kernel command line: %s\n", boot_command_line);
 	parse_early_param();
 	parse_args("Booting kernel", static_command_line, __start___param,