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

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Date:	Sun, 20 Jun 2010 15:14:46 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Michael Kerrisk <mtk.manpages@...il.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH] [31/31] HWPOISON: Add a madvise() injector for soft
 page 	offlining

On Sun, Jun 20, 2010 at 02:19:35PM +0800, Michael Kerrisk wrote:
> Hi Andi,
> On Sat, Jun 19, 2010 at 9:52 PM, Andi Kleen <andi@...stfloor.org> wrote:
> >> .TP
> >> .BR MADV_SOFT_OFFLINE " (Since Linux 2.6.33)
> >> Soft offline the pages in the range specified by
> >> .I addr
> >> and
> >> .IR length .
> >> This memory of each page in the specified range is copied to a new page,
> >
> > Actually there are some cases where it's also dropped if it's cached page.
> >
> > Perhaps better would be something more fuzzy like
> >
> > "the contents are preserved"
> 
> The problem to me is that this gets so fuzzy that it's hard to
> understand the meaning (I imagine many readers will ask: "What does it
> mean that the contents are preserved"?). Would you be able to come up
> with a wording that is a little miore detailed?

That is, MADV_SOFT_OFFLINE won't lose data.

If a process writes "1" to some virtual address and then called
madvice(MADV_SOFT_OFFLINE) on that virtual address, it can continue
to read "1" from that virtual address.

MADV_SOFT_OFFLINE "transparently" replaces the underlying physical page
frame with a new one that contains the same data "1". The original page
frame is offlined, and the new page frame may be installed lazily.

Thanks,
Fengguang
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