linux-kernel - Re: [RFC v3 3/4] mm, printk: introduce new format %pGt for page

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Message-ID: <Y6AycLbpjVzXM5I9@smile.fi.intel.com>
Date:   Mon, 19 Dec 2022 11:44:16 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Hyeonggon Yoo <42.hyeyoo@...il.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        HORIGUCHI NAOYA(堀口　直也) 
        <naoya.horiguchi@....com>, Joe Perches <joe@...ches.com>,
        Petr Mladek <pmladek@...e.com>,
        Matthew WilCox <willy@...radead.org>,
        David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC v3 3/4] mm, printk: introduce new format %pGt for page_type

On Sun, Dec 18, 2022 at 07:19:00PM +0900, Hyeonggon Yoo wrote:
> %pGp format is used 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.
> 
> 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 page type names.

...

> +#define __def_pagetype_names						\
> +	{PG_slab,			"slab"		},		\
> +	{PG_offline,			"offline"	},		\
> +	{PG_guard,			"guard"		},		\
> +	{PG_table,			"table"		},		\
> +	{PG_buddy,			"buddy"		}

Wondering if it will be more robust to define a helper macro

#define DEF_PAGETYPE_NAME(_name)	{ PG_##_name, __stringify(_name) }
...
#undef DEF_PAGETYPE_MASK

In this case it decreases the chances of typo in the strings and flags.

-- 
With Best Regards,
Andy Shevchenko