linux-kernel - Re: [PATCH 3/3] printk: dump full information of page flags in pGp

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Date:   Wed, 27 Jan 2021 18:35:53 -0800
From:   Joe Perches <joe@...ches.com>
To:     Yafang Shao <laoar.shao@...il.com>, david@...hat.com,
        vbabka@...e.cz, cl@...ux.com, penberg@...nel.org,
        rientjes@...gle.com, iamjoonsoo.kim@....com,
        akpm@...ux-foundation.org, pmladek@...e.com, rostedt@...dmis.org,
        sergey.senozhatsky@...il.com, andriy.shevchenko@...ux.intel.com,
        linux@...musvillemoes.dk
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] printk: dump full information of page flags in pGp

On Thu, 2021-01-28 at 10:19 +0800, Yafang Shao wrote:
> Currently the pGp only shows the names of page flags, rather than
> the full information including section, node, zone, last cpupid and
> kasan tag. While it is not easy to parse these information manually
> because there're so many flavors. Let's interpret them in pGp as well.
[]
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
[]
> @@ -1916,6 +1916,46 @@ char *format_flags(char *buf, char *end, unsigned long flags,
>  	return buf;
>  }
> 
> +struct page_flags_layout {
> +	int width;
> +	int shift;
> +	int mask;
> +	char *name;
> +};
> +
> +struct page_flags_layout pfl[] = {

static const struct page_flags_layout pfl[] = {

> +	{SECTIONS_WIDTH, SECTIONS_PGSHIFT, SECTIONS_MASK, "Section "},
> +	{NODES_WIDTH, NODES_PGSHIFT, NODES_MASK, "Node "},
> +	{ZONES_WIDTH, ZONES_PGSHIFT, ZONES_MASK, "Zone "},
> +	{LAST_CPUPID_WIDTH, LAST_CPUPID_PGSHIFT, LAST_CPUPID_MASK, "Lastcpupid "},
> +	{KASAN_TAG_WIDTH, KASAN_TAG_PGSHIFT, KASAN_TAG_MASK, "Kasantag "},
> +};
> +
> +static
> +char *format_layout(char *buf, char *end, unsigned long flags)

poor name.  perhaps format_page_flags

> +{
> +	int i;
> +
> +	for (i = 0; i < sizeof(pfl) / sizeof(struct page_flags_layout) && buf < end; i++) {

	for (i = 0; i < ARRAY_SIZE(pfl) && buf < end; i++) {


> @@ -1929,7 +1969,7 @@ char *flags_string(char *buf, char *end, void *flags_ptr,
>  	switch (fmt[1]) {
>  	case 'p':
>  		flags = *(unsigned long *)flags_ptr;
> -		/* Remove zone id */
> +		buf = format_layout(buf, end, flags & ~((1UL << NR_PAGEFLAGS) - 1));
>  		flags &= (1UL << NR_PAGEFLAGS) - 1;

Perhaps store the bitshift into a temp and use the temp twice

		foo = BIT(NR_PAGEFLAGS) - 1;

		buf = format_layout(buf, end, flags & ~foo);
		flags &= foo;