linux-kernel - Re: [RFC][PATCH] proc: export more page flags in /proc/kpageflags

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Date:	Tue, 14 Apr 2009 14:41:32 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [RFC][PATCH] proc: export more page flags in /proc/kpageflags

On Tue, Apr 14, 2009 at 12:37:10PM +0800, KOSAKI Motohiro wrote:
> > Export the following page flags in /proc/kpageflags,
> > just in case they will be useful to someone:
> > 
> > - PG_swapcache
> > - PG_swapbacked
> > - PG_mappedtodisk
> > - PG_reserved
> > - PG_private
> > - PG_private_2
> > - PG_owner_priv_1
> > 
> > - PG_head
> > - PG_tail
> > - PG_compound
> > 
> > - PG_unevictable
> > - PG_mlocked
> > 
> > - PG_poison
> 
> Sorry, NAK this.
> We shouldn't expose internal flags. please choice useful flags only.

OK. So are there anyone interested in any of these flags? Thanks!

My rational to export most page flags is that hopefully they could
help debugging kernel at some random situations..

> > Also add the following two pseudo page flags:
> > 
> > - PG_MMAP:   whether the page is memory mapped
> > - PG_NOPAGE: whether the page is present
> > 
> > This increases the total number of exported page flags to 25.
> > 
> > Cc: Andi Kleen <andi@...stfloor.org>
> > Cc: Matt Mackall <mpm@...enic.com>
> > Cc: Alexey Dobriyan <adobriyan@...il.com>
> > Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> > ---
> >  fs/proc/page.c |  112 +++++++++++++++++++++++++++++++++--------------
> >  1 file changed, 81 insertions(+), 31 deletions(-)
> > 
> > --- mm.orig/fs/proc/page.c
> > +++ mm/fs/proc/page.c
> > @@ -68,20 +68,86 @@ static const struct file_operations proc
> >  
> >  /* These macros are used to decouple internal flags from exported ones */
> >  
> > -#define KPF_LOCKED     0
> > -#define KPF_ERROR      1
> > -#define KPF_REFERENCED 2
> > -#define KPF_UPTODATE   3
> > -#define KPF_DIRTY      4
> > -#define KPF_LRU        5
> > -#define KPF_ACTIVE     6
> > -#define KPF_SLAB       7
> > -#define KPF_WRITEBACK  8
> > -#define KPF_RECLAIM    9
> > -#define KPF_BUDDY     10
> > +enum {
> > +	KPF_LOCKED,		/*  0 */
> > +	KPF_ERROR,		/*  1 */
> > +	KPF_REFERENCED,		/*  2 */
> > +	KPF_UPTODATE,		/*  3 */
> > +	KPF_DIRTY,		/*  4 */
> > +	KPF_LRU,		/*  5 */
> > +	KPF_ACTIVE,		/*  6 */
> > +	KPF_SLAB,		/*  7 */
> > +	KPF_WRITEBACK,		/*  8 */
> > +	KPF_RECLAIM,		/*  9 */
> > +	KPF_BUDDY,		/* 10 */
> > +	KPF_MMAP,		/* 11 */
> > +	KPF_SWAPCACHE,		/* 12 */
> > +	KPF_SWAPBACKED,		/* 13 */
> > +	KPF_MAPPEDTODISK,	/* 14 */
> > +	KPF_RESERVED,		/* 15 */
> > +	KPF_PRIVATE,		/* 16 */
> > +	KPF_PRIVATE2,		/* 17 */
> > +	KPF_OWNER_PRIVATE,	/* 18 */
> > +	KPF_COMPOUND_HEAD,	/* 19 */
> > +	KPF_COMPOUND_TAIL,	/* 20 */
> > +	KPF_UNEVICTABLE,	/* 21 */
> > +	KPF_MLOCKED,		/* 22 */
> > +	KPF_POISON,		/* 23 */
> > +	KPF_NOPAGE,		/* 24 */
> > +	KPF_NUM
> > +};
> 
> this is userland export value. then enum is wrong idea.
> explicit name-number relationship is better. it prevent unintetional
> ABI break.

Right, that's the reason I add the /* number */ comments.
Anyway, it would be better to use explicit #defines.

Thanks,
Fengguang

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