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

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

[Hyeonggon Yoo]

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

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

[Joe Perches]

On Sun, 2022-11-06 at 23:03 +0900, Hyeonggon Yoo wrote:
> 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().
[]
> diff --git 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

noinline_for_stack ?

> +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);

Might be better with something like '%pGt: no type..."

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

[Hyeonggon Yoo]

On Sun, Nov 06, 2022 at 10:04:25AM -0800, Joe Perches wrote:
> On Sun, 2022-11-06 at 23:03 +0900, Hyeonggon Yoo wrote:
> > 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().
> []
> > diff --git 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

Thanks for looking at this.

> 
> noinline_for_stack ?

May I ask why,
Does it have issues related to stack consumption?
To Be Honest I'm a bit unsure what is purpose of this attribute.

> > +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);
> 
> Might be better with something like '%pGt: no type..."

Will try something like "0x32()" when it has no type because it is
mapped to userspace.

-- 
Thanks,
Hyeonggon

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

[Petr Mladek]

On Wed 2022-11-09 15:14:05, Hyeonggon Yoo wrote:
> On Sun, Nov 06, 2022 at 10:04:25AM -0800, Joe Perches wrote:
> > On Sun, 2022-11-06 at 23:03 +0900, Hyeonggon Yoo wrote:
> > > 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().
> > []
> > > diff --git 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
> 
> Thanks for looking at this.
> 
> > 
> > noinline_for_stack ?

Honestly, I do not like much adding this without numbers. It has been added
to some functions in vsprintf.c long time ago because it reduced
the stack usage. But I think that it is a compiler and an architecture
specific. And it is not clear if it would really help in this
particular case.

Feel free to omit it.

Best Regards,
Petr

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

[Andy Shevchenko]

On Sun, Nov 06, 2022 at 11:03:55PM +0900, Hyeonggon Yoo wrote:
> 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()

Why do we have empty parentheses? I would expect either something there, or no
parentheses at all.

> [    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

Can you utilize --cc parameter next time and avoid polluting commit message
with this? We have archives where anybody can check this (and usually maintainers
add a Link tag for that purpose).

...

> +	%pGt	0xffefffff(slab)

No space before ( ?

...

> +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);

It's too long, can we make it shorten?

> +	buf = number(buf, end, page_type, default_flag_spec);
> +
> +	if (buf < end)
> +		*buf = '(';
> +	buf++;

> +	if (page_type_has_type(page_type))

This should be check for the entire function.

> +		buf = format_flags(buf, end, ~page_type, pagetype_names);
> +
> +	if (buf < end)
> +		*buf = ')';
> +	buf++;
> +
> +	return buf;
> +}

...

> @@ -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}

Hmm... I see it's already done like this above, but {}  would suffice, why not
to convert the rest first to the {} and use it here?

> +};

...

>  	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[];

I would split this to a separate change, but it's up to PRINTK maintainers.

-- 
With Best Regards,
Andy Shevchenko

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

[Petr Mladek]

On Mon 2022-11-07 13:18:52, Andy Shevchenko wrote:
> On Sun, Nov 06, 2022 at 11:03:55PM +0900, Hyeonggon Yoo wrote:
> > 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()
> 
> Why do we have empty parentheses? I would expect either something there, or no
> parentheses at all.

This looks fine. format_page_flags() does the same for %pGp.

> ...
> 
> > +	%pGt	0xffefffff(slab)
> 
> No space before ( ?

Also looks fine. %pGp does the same.

> ...
> 
> > +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);
> 
> It's too long, can we make it shorten?

I wonder if it would help to write the value. Something like:

      page_type: 0x0ace5768(no type)

That said. I am not familiar with the page types and am not sure
about the semantic of this value. MM people should decide what they
want to see in this case.

> ...
> 
> >  	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[];
> 
> I would split this to a separate change, but it's up to PRINTK maintainers.

I guess that you are talking about the line:

+	pr_warn("page_type: %pGt\n", &head->page_type);


Yes, it would be better to have implementation of %pGt modifier
in one patch and add the user in another one.

Best Regards,
Petr

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

[Andy Shevchenko]

On Mon, Nov 07, 2022 at 03:20:34PM +0100, Petr Mladek wrote:
> On Mon 2022-11-07 13:18:52, Andy Shevchenko wrote:
> > On Sun, Nov 06, 2022 at 11:03:55PM +0900, Hyeonggon Yoo wrote:
> > > dump_page() uses %pGp format to print 'flags' field of struct page.

...

> > > [    1.816443] page_type: 0xffffffff()
> > 
> > Why do we have empty parentheses? I would expect either something there, or no
> > parentheses at all.
> 
> This looks fine. format_page_flags() does the same for %pGp.

...

> > > +	%pGt	0xffefffff(slab)
> > 
> > No space before ( ?
> 
> Also looks fine. %pGp does the same.

Maybe we can modify them before or after this change?

-- 
With Best Regards,
Andy Shevchenko

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

[Hyeonggon Yoo]

On Mon, Nov 07, 2022 at 03:20:34PM +0100, Petr Mladek wrote:
> On Mon 2022-11-07 13:18:52, Andy Shevchenko wrote:
> > On Sun, Nov 06, 2022 at 11:03:55PM +0900, Hyeonggon Yoo wrote:
> > > 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()
> > 


Thank you both for looking at this! :-)

> > Why do we have empty parentheses? I would expect either something there, or no
> > parentheses at all.
> 
> This looks fine. format_page_flags() does the same for %pGp.
> 
> > ...
> > 
> > > +	%pGt	0xffefffff(slab)
> > 
> > No space before ( ?
> 
> Also looks fine. %pGp does the same.
> 
> > ...
> > 
> > > +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);
> > 
> > It's too long, can we make it shorten?
> 
> I wonder if it would help to write the value. Something like:
> 
>       page_type: 0x0ace5768(no type)
>
> That said. I am not familiar with the page types and am not sure
> about the semantic of this value. MM people should decide what they
> want to see in this case.

Hmm, then for consistency let's try:

- 0xffefffff(slab)
- 0xffffffff()
- 0x0ace5768()

this way.

> > ...
> > 
> > >  	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[];
> > 
> > I would split this to a separate change, but it's up to PRINTK maintainers.
> 
> I guess that you are talking about the line:
> 
> +	pr_warn("page_type: %pGt\n", &head->page_type);
> 
> 
> Yes, it would be better to have implementation of %pGt modifier
> in one patch and add the user in another one.

Sounds reasonable.
Will split its caller into another patch next to this one.

-- 
Thanks,
Hyeonggon