linux-kernel - Re: [RFC 5/7] LTTng instrumentation mm

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Date:	Thu, 15 Nov 2007 14:16:17 -0800
From:	Dave Hansen <haveblue@...ibm.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, mbligh@...gle.com
Subject: Re: [RFC 5/7] LTTng instrumentation mm

On Thu, 2007-11-15 at 16:51 -0500, Mathieu Desnoyers wrote:
> * Dave Hansen (haveblue@...ibm.com) wrote:
> > > On Tue, 2007-11-13 at 14:33 -0500, Mathieu Desnoyers wrote:
> > >  linux-2.6-lttng/mm/page_io.c        2007-11-13 09:49:35.000000000 -0500
> > > @@ -114,6 +114,7 @@ int swap_writepage(struct page *page, st
> > >                 rw |= (1 << BIO_RW_SYNC);
> > >         count_vm_event(PSWPOUT);
> > >         set_page_writeback(page);
> > > +       trace_mark(mm_swap_out, "address %p", page_address(page));
> > >         unlock_page(page);
> > >         submit_bio(rw, bio);
> > >  out:
> > 
> > I'm not sure all this page_address() stuff makes any sense on highmem
> > systems.  How about page_to_pfn()?
>
> Knowing which page frame number has been swapped out is not always as
> relevant as knowing the page's virtual address (when it has one). Saving
> both the PFN and the page's virtual address could give us useful
> information when the page is not mapped.

For most (all?) architectures, the PFN and the virtual address in the
kernel's linear are interchangeable with pretty trivial arithmetic.  All
pages have a pfn, but not all have a virtual address.  Thus, I suggested
using the pfn.  What kind of virtual addresses are you talking about?

-- Dave

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