Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Message-ID: <e5ea9e8b1190c2a397a1b84dd55bb9c706dc7058.camel@perches.com>
Subject: Re: [PATCH 3/3] printk: dump full information of page flags in pGp
From:   Joe Perches <joe@perches.com>
To:     Yafang Shao <laoar.shao@gmail.com>, david@redhat.com,
        vbabka@suse.cz, cl@linux.com, penberg@kernel.org,
        rientjes@google.com, iamjoonsoo.kim@lge.com,
        akpm@linux-foundation.org, pmladek@suse.com, rostedt@goodmis.org,
        sergey.senozhatsky@gmail.com, andriy.shevchenko@linux.intel.com,
        linux@rasmusvillemoes.dk
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org
Date:   Wed, 27 Jan 2021 18:35:53 -0800
In-Reply-To: <20210128021947.22877-4-laoar.shao@gmail.com>
References: <20210128021947.22877-1-laoar.shao@gmail.com>
         <20210128021947.22877-4-laoar.shao@gmail.com>
Content-Type: text/plain; charset="ISO-8859-1"
User-Agent: Evolution 3.38.1-1 
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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;