linux-kernel - Re: [PATCH 10/11] maps3: add /proc/kpagecount and /proc/kpageflags interfaces

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Message-ID: <20071016005832.GD19691@waste.org>
Date:	Mon, 15 Oct 2007 19:58:32 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Dave Hansen <haveblue@...ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	David Rientjes <rientjes@...gle.com>,
	Fengguang Wu <wfg@...l.ustc.edu.cn>
Subject: Re: [PATCH 10/11] maps3: add /proc/kpagecount and /proc/kpageflags interfaces

On Mon, Oct 15, 2007 at 05:49:10PM -0700, Dave Hansen wrote:
> On Mon, 2007-10-15 at 19:35 -0500, Matt Mackall wrote:
> > Perhaps we need something like:
> > 
> > flags = page->flags;
> > userflags = 
> >           FLAG_BIT(USER_REFERENCED, flags & PG_referenced) |
> >           ...
> > 
> > etc. for the flags we want to export. This will let us change to
> > 
> >          FLAG_BIT(USER_SLAB, PageSlab(page)) |
> > 
> > if we make a virtual slab bit.
> 
> Yeah, that looks like a pretty sane scheme.  Do we want to be any more
> abstract about it?  Perhaps instead of USER_SLAB, it should be
> USER_KERNEL_INTERNAL, or USER_KERNEL_USE.  The slab itself is going away
> as we speak. :)

Perhaps. SLUB is still "a slab-based allocator". SLOB isn't, but I
intend to start making it use PG_slab shortly anyway.
 
> > And it shows up in grep.
> > 
> > Unfortunately, i386 test_bit is an asm inline and not a macro so we
> > can't hope for the compiler to fold up a bunch of identity bit
> > mappings for us. 
> 
> We could also Yeah, that looks like a pretty sane scheme.  Do we want to
> be any more abstract about it?  Perhaps instead of USER_SLAB, it should
> be USER_KERNEL_INTERNAL, or USER_KERNEL_USE.  The slab itself is going
> away as we speak.
> 
> For the bits that we want to export, we could also add the unoptimized
> access functions for any that don't already have them:
> 
> #define __ClearPageReserved(page)       __clear_bit(PG_reserved, &(page)->flags)

Confused. Why are we interested in clear?

-- 
Mathematics is the supreme nostalgia of our time.
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