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

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Date:	Wed, 2 Dec 2015 22:04:25 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	yalin wang <yalin.wang2010@...il.com>
Cc:	linux-mm@...ck.org, 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 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;
> struct trace_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?

I could maybe accept passing a flag value and trace_print_flags * as two
separate parameters, but I guess that breaks an ancient invariant of one
parameter per format string...

> Thanks
> 
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