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

[Wu Fengguang <fengguang.wu@intel.com>]

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@firstfloor.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