Subject: Re: [PATCH 1/2] mm, printk: introduce new format string for flags
To: yalin wang <yalin.wang2010@gmail.com>
References: <20151125143010.GI27283@dhcp22.suse.cz>
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Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>, Minchan Kim <minchan@kernel.org>,
        Sasha Levin <sasha.levin@oracle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@suse.cz>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>
From: Vlastimil Babka <vbabka@suse.cz>
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Date: Wed, 2 Dec 2015 22:04:25 +0100
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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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