linux-kernel - Re: [PATCH 0/3] /proc/kmem cleanups and hwpoison bits

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Date:	Wed, 16 Sep 2009 11:01:17 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Hugh Dickins <hugh.dickins@...cali.co.uk>
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ingo Molnar <mingo@...e.hu>, Tejun Heo <tj@...nel.org>,
	Nick Piggin <npiggin@...e.de>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-m68k@...ts.linux-m68k.org, sparclinux@...r.kernel.org
Subject: Re: [PATCH 0/3] /proc/kmem cleanups and hwpoison bits

On Tue, Sep 15, 2009 at 12:16, Hugh Dickins <hugh.dickins@...cali.co.uk> wrote:
> On Tue, 15 Sep 2009, Wu Fengguang wrote:
>> On Tue, Sep 15, 2009 at 11:09:39AM +0800, KAMEZAWA Hiroyuki wrote:
>> > On Tue, 15 Sep 2009 10:18:51 +0800
>> > Wu Fengguang <fengguang.wu@...el.com> wrote:
>> >
>> > > Hi Kame,
>> > >
>> > > Here are 3 more kmem patches in my queue. Comments are welcome.
>> > > If you feel good about them, I can send all recent kmem cleanup
>> > > patches for you.
>> > >
>> >
>> > This is my quick hack. But I don't want to be an obstacle for you.
>> > So, I'll wait for your updates.
>>
>> Thanks. This is also a bug fix: vmalloc_to_page() will otherwise BUG()
>> on !is_vmalloc_or_module_addr() pages.
>>
>> > ==
>> > Now, /dev/kmem's read/write vmalloc area doesn't do
>> > range-check. Because vread/vwrite traverse vmalloc area list
>> > under system-wide spinlock, it's better to avoid unnecessary
>> > to do unnecessary calls to vread/vwrite.
>>
>> is_vmalloc_or_module_addr() could be put to either read_kmem()
>> or aligned_vread(), and I'm fine with both.
>>
>> It looks like vread can be shared by kmem and kcore :)
>>
>> > And, vread/vwrite returns 0 if we accessed memory holes.
>> > We can avoid copy-to-user in read side, we just ignore at write.
>> >
>> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>> > ---
>> >  drivers/char/mem.c |   27 +++++++++++++++++++--------
>> >  1 file changed, 19 insertions(+), 8 deletions(-)
>
> Sorry guys, I'm picking this mail pretty much at random
> as something to reply to.
>
> I'm interested to notice such work going on in drivers/char/mem.c,
> and don't have time to join in - you interact a lot faster than I
> manage, and I've other priorities to attend to; but thought I should
> at least send over the patch I've been including in my private debug
> kernels for the last couple of years (rebased to 2.6.31), which lets
> me peek and poke into /dev/kmem as I occasionally wish.
>
> Warning: it may be rubbish, it may just be a hack which appeared to
> work for me the last time I tried, on a particular address range of a
> particular set of configurations of a particular set of architectures
> (x86_32, x86_64, powerpc64).  I've never thought it through enough to
> consider submitting, but it _might_ contain something useful for you
> to factor into your own efforts.
>
> Sorry for chucking it over the wall to you in this way, but I guess
> that's better than just sitting quietly on it for a few more years.
>
> Certainly-Not-Signed-off-by: Hugh Dickins <hugh.dickins@...cali.co.uk>
> ---
>
>  drivers/char/mem.c |  265 +++++++++++++++----------------------------
>  fs/read_write.c    |    9 +
>  2 files changed, 105 insertions(+), 169 deletions(-)
>
> but if completed would also remove vread() and vwrite() from
>
>  include/linux/vmalloc.h
>  mm/nommu.c
>  mm/vmalloc.c
>
> --- 2.6.31/drivers/char/mem.c   2009-09-09 23:13:59.000000000 +0100
> +++ 2.6.31d/drivers/char/mem.c  2009-09-10 09:38:30.000000000 +0100

> -#ifdef __ARCH_HAS_NO_PAGE_ZERO_MAPPED
> -               /* we don't have page 0 mapped on sparc and m68k.. */

Is this `feature' removed?

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds
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