mm, printk: introduce new format string for flags

In mm we use several kinds of flags bitfields that are sometimes printed
for debugging purposes, or exported to userspace via sysfs.  To make
them easier to interpret independently on kernel version and config, we
want to dump also the symbolic flag names.  So far this has been done
with repeated calls to pr_cont(), which is unreliable on SMP, and not
usable for e.g.  sysfs export.

To get a more reliable and universal solution, this patch extends
printk() format string for pointers to handle the page flags (%pGp),
gfp_flags (%pGg) and vma flags (%pGv).  Existing users of
dump_flag_names() are converted and simplified.

It would be possible to pass flags by value instead of pointer, but the
%p format string for pointers already has extensions for various kernel
structures, so it's a good fit, and the extra indirection in a
non-critical path is negligible.

[linux@rasmusvillemoes.dk: lots of good implementation suggestions]
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
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, 53 insertions, 0 deletions

diff --git a/lib/test_printf.c b/lib/test_printf.c
index 4f6ae60433bc..563f10e6876a 100644
--- a/lib/test_printf.c
+++ b/lib/test_printf.c
@@ -17,6 +17,9 @@
 #include <linux/socket.h>
 #include <linux/in.h>
 
+#include <linux/gfp.h>
+#include <linux/mm.h>
+
 #define BUF_SIZE 256
 #define PAD_SIZE 16
 #define FILL_CHAR '$'
@@ -411,6 +414,55 @@ netdev_features(void)
 }
 
 static void __init
+flags(void)
+{
+	unsigned long flags;
+	gfp_t gfp;
+	char *cmp_buffer;
+
+	flags = 0;
+	test("", "%pGp", &flags);
+
+	/* Page flags should filter the zone id */
+	flags = 1UL << NR_PAGEFLAGS;
+	test("", "%pGp", &flags);
+
+	flags |= 1UL << PG_uptodate | 1UL << PG_dirty | 1UL << PG_lru
+		| 1UL << PG_active | 1UL << PG_swapbacked;
+	test("uptodate|dirty|lru|active|swapbacked", "%pGp", &flags);
+
+
+	flags = VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC
+			| VM_DENYWRITE;
+	test("read|exec|mayread|maywrite|mayexec|denywrite", "%pGv", &flags);
+
+	gfp = GFP_TRANSHUGE;
+	test("GFP_TRANSHUGE", "%pGg", &gfp);
+
+	gfp = GFP_ATOMIC|__GFP_DMA;
+	test("GFP_ATOMIC|GFP_DMA", "%pGg", &gfp);
+
+	gfp = __GFP_ATOMIC;
+	test("__GFP_ATOMIC", "%pGg", &gfp);
+
+	cmp_buffer = kmalloc(BUF_SIZE, GFP_KERNEL);
+	if (!cmp_buffer)
+		return;
+
+	/* Any flags not translated by the table should remain numeric */
+	gfp = ~__GFP_BITS_MASK;
+	snprintf(cmp_buffer, BUF_SIZE, "%#lx", (unsigned long) gfp);
+	test(cmp_buffer, "%pGg", &gfp);
+
+	snprintf(cmp_buffer, BUF_SIZE, "__GFP_ATOMIC|%#lx",
+							(unsigned long) gfp);
+	gfp |= __GFP_ATOMIC;
+	test(cmp_buffer, "%pGg", &gfp);
+
+	kfree(cmp_buffer);
+}
+
+static void __init
 test_pointer(void)
 {
 	plain();
@@ -428,6 +480,7 @@ test_pointer(void)
 	struct_clk();
 	bitmap();
 	netdev_features();
+	flags();
 }
 
 static int __init