[31/31] HWPOISON: Add a madvise() injector for soft page offlining
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From: Wu Fengguang on 20 Jun 2010 03:20 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(a)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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Wu Fengguang on 26 Jun 2010 19:40
On Sat, Jun 26, 2010 at 09:18:52PM +0800, Michael Kerrisk wrote: > Hi Fengguang, > > On Sun, Jun 20, 2010 at 9:14 AM, Wu Fengguang <fengguang.wu(a)intel.com> wrote: > > 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(a)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. That helps me come up with a description that is I think a bit clearer: > > MADV_SOFT_OFFLINE (Since Linux 2.6.33) > Soft offline the pages in the range specified by > addr and length. The memory of each page in the > specified range is preserved (i.e., when next > accessed, the same content will be visible, but > in a new physical page frame), and the original > page is offlined (i.e., no longer used, and > taken out of normal memory management). The > effect of the MADV_SOFT_OFFLINE operation is > invisible to (i.e., does not change the seman- > tics of) the calling process. ... > > The actual patch for man-pages-3.26 is below. Thanks. The change looks good to me. Note that the other perceivable change may be a little access delay. The kernel could choose to simply drop the in-memory data when there is another copy in disk. When accessed again, the content for the new physical page will be populated from disk IO. Thanks, Fengguang > > --- a/man2/madvise.2 > +++ b/man2/madvise.2 > @@ -163,12 +163,14 @@ Soft offline the pages in the range specified by > .I addr > and > .IR length . > -The memory of each page in the specified range is copied to a new page, > +The memory of each page in the specified range is preserved > +(i.e., when next accessed, the same content will be visible, > +but in a new physical page frame), > and the original page is offlined > (i.e., no longer used, and taken out of normal memory management). > The effect of the > .B MADV_SOFT_OFFLINE > -operation is normally invisible to (i.e., does not change the semantics of) > +operation is invisible to (i.e., does not change the semantics of) > the calling process. > This feature is intended for testing of memory error-handling code; > it is only available if the kernel was configured with -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |