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

Andy Shevchenko
2022-11-07T11:19:05Z

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