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

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Date:   Mon, 19 Dec 2022 11:35:38 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        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 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