linux-kernel - Re: [PATCH 1/2] mm, printk: introduce new format string for flags

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Message-Id: <1F60C207-1CC2-4B28-89AC-58C72D95A39D@gmail.com>
Date:	Wed, 2 Dec 2015 16:11:58 -0800
From:	yalin wang <yalin.wang2010@...il.com>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	"open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Minchan Kim <minchan@...nel.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...e.cz>,
	Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH 1/2] mm, printk: introduce new format string for flags


> On Dec 2, 2015, at 13:04, Vlastimil Babka <vbabka@...e.cz> wrote:
> 
> On 12/02/2015 06:40 PM, yalin wang wrote:
> 
> (please trim your reply next time, no need to quote whole patch here)
> 
>> i am thinking why not make %pg* to be more generic ?
>> not restricted to only GFP / vma flags / page flags .
>> so could we change format like this ?
>> define a flag spec struct to include flag and trace_print_flags and some other option :
>> typedef struct { 
>> unsigned long flag;
>> structtrace_print_flags *flags;
>> unsigned long option; } flag_sec;
>> flag_sec my_flag;
>> in printk we only pass like this :
>> printk(“%pg\n”, &my_flag) ;
>> then it can print any flags defined by user .
>> more useful for other drivers to use .
> 
> I don't know, it sounds quite complicated given that we had no flags printing
> for years and now there's just three kinds of them. The extra struct flag_sec is
> IMHO nuissance. No other printk format needs such thing AFAIK? For example, if I
> were to print page flags from several places, each would have to define the
> struct flag_sec instance, or some header would have to provide it?
this can be avoided by provide a macro in header file .
we can add a new struct to declare trace_print_flags :
for example:
#define DECLARE_FLAG_PRINTK_FMT(name, flags_array)   flag_spec name = { .flags = flags_array};
#define FLAG_PRINTK_FMT(name, flag) ({  name.flag = flag;  &name})

in source code :
DECLARE_FLAG_PRINTK_FMT(my_flag, vmaflags_names);
printk(“%pg\n”, FLAG_PRINTK_FMT(my_flag, vma->flag));

i am not if DECLARE_FLAG_PRINTK_FMT and FLAG_PRINTK_FMT macro 
can be defined into one macro ?
maybe need some trick here .

is it possible ?


Thanks



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