On Tue, 26 Jan 2016, Heiko Carstens wrote:

On Tue, Jan 26, 2016 at 10:18:25AM +0100, Christian Borntraeger wrote:

quoted

We can use debug_pagealloc_enabled() to check if we can map
the identity mapping with 1MB/2GB pages as well as to print
the current setting in dump_stack.

Signed-off-by: Christian Borntraeger <redacted>
---
 arch/s390/kernel/dumpstack.c |  4 +++-
 arch/s390/mm/vmem.c          | 10 ++++------
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/arch/s390/kernel/dumpstack.c b/arch/s390/kernel/dumpstack.c
index dc8e204..a1c0530 100644
--- a/arch/s390/kernel/dumpstack.c
+++ b/arch/s390/kernel/dumpstack.c

@@ -11,6 +11,7 @@
 #include <linux/export.h>
 #include <linux/kdebug.h>
 #include <linux/ptrace.h>
+#include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/sched.h>
 #include <asm/processor.h>

@@ -186,7 +187,8 @@ void die(struct pt_regs *regs, const char *str)
 	printk("SMP ");
 #endif
 #ifdef CONFIG_DEBUG_PAGEALLOC
-	printk("DEBUG_PAGEALLOC");
+	printk("DEBUG_PAGEALLOC(%s)",
+		debug_pagealloc_enabled() ? "enabled" : "disabled");
 #endif

I'd prefer if you change this to

	if (debug_pagealloc_enabled())
		printk("DEBUG_PAGEALLOC");

That way we can get rid of yet another ifdef. Having
"DEBUG_PAGEALLOC(disabled)" doesn't seem to be very helpful.

I'd agree if CONFIG_DEBUG_PAGEALLOC only did anything when 
debug_pagealloc_enabled() is true, but that doesn't seem to be the case.  
When CONFIG_DEBUG_SLAB is enabled, for instance, CONFIG_DEBUG_PAGEALLOC 
also enables stackinfo storing and poisoning and it's not guarded by 
debug_pagealloc_enabled().

It seems like CONFIG_DEBUG_PAGEALLOC enables debugging functionality 
outside the scope of the debug_pagealloc=on kernel parameter, so 
DEBUG_PAGEALLOC(disabled) actually does mean something.

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