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Date:   Mon, 19 Dec 2022 11:35:38 -0800
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Subject: Re: [RFC v3 3/4] mm, printk: introduce new format %pGt for page_type
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To:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc:     Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= 
        <naoya.horiguchi@nec.com>, Joe Perches <joe@perches.com>,
        Petr Mladek <pmladek@suse.com>,
        Matthew WilCox <willy@infradead.org>,
        David Hildenbrand <david@redhat.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
References: <20221218101901.373450-1-42.hyeyoo@gmail.com>
 <20221218101901.373450-4-42.hyeyoo@gmail.com>
 <Y6AycLbpjVzXM5I9@smile.fi.intel.com>
From:   Randy Dunlap <rdunlap@infradead.org>
In-Reply-To: <Y6AycLbpjVzXM5I9@smile.fi.intel.com>
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On 12/19/22 01:44, Andy Shevchenko wrote:
> 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.

I'd say Yes.  (and #undef DEF_PAGETYPE_NAME methinks; or change both to _MASK)

-- 
~Randy