linux-kernel - Re: [RFC] Refactor kenter/kleave/kdebug macros

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Date:	Mon, 18 May 2015 16:20:36 +0100
From:	David Howells <dhowells@...hat.com>
To:	Leon Romanovsky <leon@...n.nu>
Cc:	dhowells@...hat.com, Linux-MM <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-cachefs <linux-cachefs@...hat.com>,
	linux-afs <linux-afs@...ts.infradead.org>
Subject: Re: [RFC] Refactor kenter/kleave/kdebug macros

Leon Romanovsky <leon@...n.nu> wrote:

> >> Additionally, It looks like the output of these macros can be viewed by
> >> ftrace mechanism.
> >
> > *blink* It can?
> I was under strong impression that "function" and "function_graph"
> tracers will give similar kenter/kleave information. Do I miss
> anything important, except the difference in output format?
> 
> >
> >> Maybe we should delete them from mm/nommu.c as was pointed by Joe?
> >
> > Why?
> If ftrace is sufficient to get the debug information, there will no
> need to duplicate it.

It isn't sufficient.  It doesn't store the parameters or the return value, it
doesn't distinguish the return path in a function when there's more than one,
eg.:

		kleave(" = %d [val]", ret);

vs:

	kleave(" = %lx", result);

in do_mmap_pgoff() and it doesn't permit you to retrieve data from where the
argument pointers that you don't have pointed to, eg.:

	kenter("%p{%d}", region, region->vm_usage);

David
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