linux-kernel - Re: [PATCH] [31/31] HWPOISON: Add a madvise() injector for soft page offlining

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Date:	Sat, 19 Jun 2010 15:43:28 +0200
From:	Michael Kerrisk <mtk.manpages@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	fengguang.wu@...el.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] [31/31] HWPOISON: Add a madvise() injector for soft page 
	offlining

Hi Andi,

On Sat, Jun 19, 2010 at 3:30 PM, Andi Kleen <andi@...stfloor.org> wrote:
> On Sat, Jun 19, 2010 at 03:25:16PM +0200, Michael Kerrisk wrote:
>> Hi Andi,
>>
>> Thanks for this. Some comments below.
>>
>> On Sat, Jun 19, 2010 at 3:20 PM, Andi Kleen <andi@...stfloor.org> wrote:
>> > On Sat, Jun 19, 2010 at 02:36:28PM +0200, Michael Kerrisk wrote:
>> >> Hi Andi,
>> >>
>> >> On Tue, Dec 8, 2009 at 11:16 PM, Andi Kleen <andi@...stfloor.org> wrote:
>> >> >
>> >> > Process based injection is much easier to handle for test programs,
>> >> > who can first bring a page into a specific state and then test.
>> >> > So add a new MADV_SOFT_OFFLINE to soft offline a page, similar
>> >> > to the existing hard offline injector.
>> >>
>> >> I see that this made its way into 2.6.33. Could you write a short
>> >> piece on it for the madvise.2 man page?
>> >
>> > Also fixed the previous snippet slightly.
>>
>> (thanks)
>>
>> > commit edb43354f0ffc04bf4f23f01261f9ea9f43e0d3d
>> > Author: Andi Kleen <ak@...ux.intel.com>
>> > Date:   Sat Jun 19 15:19:28 2010 +0200
>> >
>> >    MADV_SOFT_OFFLINE
>> >
>> >    Signed-off-by: Andi Kleen <ak@...ux.intel.com>
>> >
>> > diff --git a/man2/madvise.2 b/man2/madvise.2
>> > index db29feb..9dccd97 100644
>> > --- a/man2/madvise.2
>> > +++ b/man2/madvise.2
>> > @@ -154,7 +154,15 @@ processes.
>> >  This operation may result in the calling process receiving a
>> >  .B SIGBUS
>> >  and the page being unmapped.
>> > -This feature is intended for memory testing.
>> > +This feature is intended for testing of memory error handling code.
>> > +This feature is only available if the kernel was configured with
>> > +.BR CONFIG_MEMORY_FAILURE .
>> > +.TP
>> > +.BR MADV_SOFT_OFFLINE " (Since Linux 2.6.33)
>> > +Soft offline a page. This will result in the memory of the page
>> > +being copied to a new page and original page be offlined. The operation
>>
>> Can you explain the term "offlined" please.
>
> The memory is not used anymore and taken out of normal
> memory management (until unpoisoned)

Is there a userspace operation to unpoison (i.e., reverse MADV_SOFT_OFFLINE)?

I ask because I wondered if there is something additional to be documented.

> and the "HardwareCorrupted:" counter in /proc/meminfo increases
>
> (don't put the later in, I'm thinking about changing that)

Okay.

>>
>> > +should be transparent to the calling process.
>>
>> Does "should be transparent" mean "is normally invisible"?
>
> Yes. It's similar to being swapped out and swapped in again.

Okay.

Thanks,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Author of "The Linux Programming Interface" http://blog.man7.org/
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