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From: Michael Kerrisk on 26 Jun 2010 09:20 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. Cheers, Michael --- 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/
From: Michael Kerrisk on 27 Jun 2010 00:40
On Sun, Jun 27, 2010 at 1:30 AM, Wu Fengguang <fengguang.wu(a)intel.com> wrote: > 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. Thanks for checking it. > 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. Yes, I'd suposed as much, but decided that was a detail that probably didm\t need to be mentioned in tha man page. Thanks, Michael >> >> --- 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 > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Author of "The Linux Programming Interface" http://blog.man7.org/ -- 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/ |