linux-kernel - Re: [PATCH 5/5] proc: export more page flags in /proc/kpageflags

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Date:	Thu, 30 Apr 2009 09:00:20 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Matt Mackall <mpm@...enic.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andi Kleen <andi@...stfloor.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 5/5] proc: export more page flags in /proc/kpageflags

On Thu, Apr 30, 2009 at 03:13:56AM +0800, Matt Mackall wrote:
> On Wed, 2009-04-29 at 16:05 +0800, Wu Fengguang wrote:
> > On Wed, Apr 29, 2009 at 01:49:21AM +0800, Matt Mackall wrote:
> > > On Tue, 2009-04-28 at 09:09 +0800, Wu Fengguang wrote:
> > > > plain text document attachment (kpageflags-extending.patch)
> > > > Export 9 page flags in /proc/kpageflags, and 8 more for kernel developers.
> > > 
> > > My only concern with this patch is it knows a bit too much about SLUB
> > > internals (and perhaps not enough about SLOB, which also overloads
> > > flags). 
> > 
> > Yup. PG_private=PG_slob_free is not masked because SLOB actually does
> > not set PG_slab at all. I wonder if it's safe to do this change:
> > 
> >         /* SLOB */
> > -       PG_slob_page = PG_active,
> > +       PG_slob_page = PG_slab,
> >         PG_slob_free = PG_private,
> 
> Yep.

OK. I'll do it - for consistency.

> > In the page-types output:
> > 
> >          flags  page-count       MB  symbolic-flags                     long-symbolic-flags
> > 0x000800000040        7113       27  ______A_________________P____      active,private
> > 0x000000000040          66        0  ______A______________________      active
> > 
> > The above two lines are obviously for SLOB pages.  It indicates lots of
> > free SLOB pages. So my question is:
> 
> Free here just means partially allocated.

Yes, I realized this when lying in bed ;-)

> > - Do you have other means to get the nr_free_slobs info? (I found none in the code)
> > or
> > - Will exporting the SL*B overloaded flags going to help?
> 
> Yes, it's useful.

Thank you. SLUB/SLOB overload different page flags, so it's possible
for user space tools to restore their real meanings - ugly but useful.

Thanks,
Fengguang
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