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

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Message-ID: <20090414071159.GV14687@one.firstfloor.org>
Date:	Tue, 14 Apr 2009 09:11:59 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	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 03:54:40PM +0900, KOSAKI Motohiro wrote:
> Hi

There are two use cases here:

First what is useful for the administrator as a general abstraction.
And what is useful for the kernel hacker for debugging.

The kernel hacker wants everything even if it's subject to change,
the administrator wants a higher level abstraction they can make
sense of and that doesn't change too often.

I think there's a case for both usages, but perhaps they 
should be separated (in a public and a internal interface perhaps?)

My comments below are about abstractions for the first case.

> 
> > 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_reserved should be exported as PG_KERNEL or somesuch.

> > > > - PG_private
> > > > - PG_private_2
> > > > - PG_owner_priv_1
> > > > 
> > > > - PG_head
> > > > - PG_tail
> > > > - PG_compound

I would combine these three into a pseudo "large page" flag.

> > > > 
> > > > - PG_unevictable
> > > > - PG_mlocked
> > > > 
> > > > - PG_poison

PG_poison is also useful to export. But since it depends on my
patchkit I will pull a patch for that into the HWPOISON series.

> > > > - PG_unevictable
> > > > - PG_mlocked
> 
> this 9 flags shouldn't exported.
> I can't imazine administrator use what purpose those flags.

I think an abstraced "PG_pinned" or somesuch flag that combines
page lock, unevictable, mlocked would be useful for the administrator.

-Andi
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