[RFC v2 3/3] mm, printk: introduce new format %pGt for page_type

Hyeonggon Yoo
2022-11-06T14:06:00Z

dump_page() uses %pGp format to print 'flags' field of struct page.
As some page flags (e.g. PG_buddy, see page-flags.h for more details)
are set in page_type field, introduce %pGt format which provides
human readable output of page_type. And use it in dump_page().

Note that the sense of bits are different in page_type. if page_type is
0xffffffff, no flags are set. if PG_slab (0x00100000) flag is set,
page_type is 0xffefffff. Clearing a bit means we set the bit. Bits in
page_type are inverted when printing type names.

Below is examples of dump_page(). One is just after alloc_pages() and
the other is after __SetPageSlab().

[ 1.814728] page:ffffea000415e200 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x105788
[ 1.815961] flags: 0x17ffffc0000000(node=0|zone=2|lastcpupid=0x1fffff)
[ 1.816443] page_type: 0xffffffff()
[ 1.816704] raw: 0017ffffc0000000 0000000000000000 dead000000000122 0000000000000000
[ 1.817291] raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
[ 1.817870] page dumped because: Before __SetPageSlab()

[ 1.818258] page:ffffea000415e200 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x105788
[ 1.818857] flags: 0x17ffffc0000000(node=0|zone=2|lastcpupid=0x1fffff)
[ 1.819250] page_type: 0xffefffff(slab)
[ 1.819483] raw: 0017ffffc0000000 0000000000000000 dead000000000122 0000000000000000
[ 1.819947] raw: 0000000000000000 0000000000000000 00000001ffefffff 0000000000000000
[ 1.820410] page dumped because: After __SetPageSlab()

Cc: Petr Mladek <pmladek@suse.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org
Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
---
Documentation/core-api/printk-formats.rst | 3 ++-
lib/test_printf.c | 23 ++++++++++++++++++++++
lib/vsprintf.c | 24 +++++++++++++++++++++++
mm/debug.c | 7 +++++++
mm/internal.h | 1 +
5 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
index dbe1aacc79d0..582e965508eb 100644
--- a/Documentation/core-api/printk-formats.rst
+++ b/Documentation/core-api/printk-formats.rst
@@ -575,12 +575,13 @@ The field width is passed by value, the bitmap is passed by reference.
Helper macros cpumask_pr_args() and nodemask_pr_args() are available to ease
printing cpumask and nodemask.

-Flags bitfields such as page flags, gfp_flags
+Flags bitfields such as page flags, page_type, gfp_flags
---------------------------------------------

::

%pGp 0x17ffffc0002036(referenced|uptodate|lru|active|private|node=0|zone=2|lastcpupid=0x1fffff)
+ %pGt 0xffefffff(slab)
%pGg GFP_USER|GFP_DMA32|GFP_NOWARN
%pGv read|exec|mayread|maywrite|mayexec|denywrite

diff --git a/lib/test_printf.c b/lib/test_printf.c
index fe13de1bed5f..6b778a8ea44c 100644
--- a/lib/test_printf.c
+++ b/lib/test_printf.c
@@ -654,12 +654,26 @@ page_flags_test(int section, int node, int zone, int last_cpupid,
test(cmp_buf, "%pGp", &flags);
}

+static void __init page_type_test(unsigned int page_type, const char *name,
+ char *cmp_buf)
+{
+ unsigned long size;
+
+ size = scnprintf(cmp_buf, BUF_SIZE, "%#x(", page_type);
+ if (page_type_has_type(page_type))
+ size += scnprintf(cmp_buf + size, BUF_SIZE - size, "%s", name);
+
+ snprintf(cmp_buf + size, BUF_SIZE - size, ")");
+ test(cmp_buf, "%pGt", &page_type);
+}
+
static void __init
flags(void)
{
unsigned long flags;
char *cmp_buffer;
gfp_t gfp;
+ unsigned int page_type;

cmp_buffer = kmalloc(BUF_SIZE, GFP_KERNEL);
if (!cmp_buffer)
@@ -699,6 +713,15 @@ flags(void)
gfp |= __GFP_HIGH;
test(cmp_buffer, "%pGg", &gfp);

+ page_type = ~0;
+ page_type_test(page_type, "", cmp_buffer);
+
+ page_type = ~PG_slab;
+ page_type_test(page_type, "slab", cmp_buffer);
+
+ page_type = ~(PG_slab | PG_table | PG_buddy);
+ page_type_test(page_type, "slab|table|buddy", cmp_buffer);
+
kfree(cmp_buffer);
}

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 24f37bab8bc1..d855b40e5cfd 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -2056,6 +2056,28 @@ char *format_page_flags(char *buf, char *end, unsigned long flags)
return buf;
}

+static
+char *format_page_type(char *buf, char *end, unsigned int page_type)
+{
+ if (!(page_type & PAGE_TYPE_BASE))
+ return string(buf, end, "no type for user-mapped page", default_str_spec);
+
+ buf = number(buf, end, page_type, default_flag_spec);
+
+ if (buf < end)
+ *buf = '(';
+ buf++;
+
+ if (page_type_has_type(page_type))
+ buf = format_flags(buf, end, ~page_type, pagetype_names);
+
+ if (buf < end)
+ *buf = ')';
+ buf++;
+
+ return buf;
+}
+
static noinline_for_stack
char *flags_string(char *buf, char *end, void *flags_ptr,
struct printf_spec spec, const char *fmt)
@@ -2069,6 +2091,8 @@ char *flags_string(char *buf, char *end, void *flags_ptr,
switch (fmt[1]) {
case 'p':
return format_page_flags(buf, end, *(unsigned long *)flags_ptr);
+ case 't':
+ return format_page_type(buf, end, *(unsigned int *)flags_ptr);
case 'v':
flags = *(unsigned long *)flags_ptr;
names = vmaflag_names;
diff --git a/mm/debug.c b/mm/debug.c
index 0fd15ba70d16..bb7f2278abc5 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -36,6 +36,11 @@ const struct trace_print_flags pageflag_names[] = {
{0, NULL}
};

+const struct trace_print_flags pagetype_names[] = {
+ __def_pagetype_names,
+ {0, NULL}
+};
+
const struct trace_print_flags gfpflag_names[] = {
__def_gfpflag_names,
{0, NULL}
@@ -114,6 +119,8 @@ static void __dump_page(struct page *page)

pr_warn("%sflags: %pGp%s\n", type, &head->flags,
page_cma ? " CMA" : "");
+ pr_warn("page_type: %pGt\n", &head->page_type);
+
print_hex_dump(KERN_WARNING, "raw: ", DUMP_PREFIX_NONE, 32,
sizeof(unsigned long), page,
sizeof(struct page), false);
diff --git a/mm/internal.h b/mm/internal.h
index cb4c663a714e..956eaa9f12c0 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -773,6 +773,7 @@ static inline void flush_tlb_batched_pending(struct mm_struct *mm)
#endif /* CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH */

extern const struct trace_print_flags pageflag_names[];
+extern const struct trace_print_flags pagetype_names[];
extern const struct trace_print_flags vmaflag_names[];
extern const struct trace_print_flags gfpflag_names[];

--
2.32.0