Hi Hugh, On Sun, Jun 20, 2010 at 2:02 AM, Hugh Dickins <hughd@xxxxxxxxxx> wrote: > Hi Michael, > > On Sat, 19 Jun 2010, Michael Kerrisk wrote: > >> Hello Hugh, Izik >> >> For the MADV_MERGEABLE + MADV_UNMERGEABLE changes added in 2.6.32, >> I've written the following man-pages text. Could you please >> review/fix/ACK. > > Ah, good, thanks for writing this (but I recognize many of the words ;)) (Yes ;-).) >> Thanks to Andi and Andrew for pointers that this documentation was needed. > > (We did Cc you when ksm.txt went into Andrew's tree, and when it went > on into Linus's tree: is there something more we should have done?) Ahh -- I missed that the CC came from you. (There is currently a big backlog.) >> --- a/man2/madvise.2 >> +++ b/man2/madvise.2 >> @@ -156,6 +157,42 @@ and the page being unmapped. >> This feature is intended for memory testing. >> This feature is only available if the kernel was configured with >> .BR CONFIG_MEMORY_FAILURE . >> +.TP >> +.BR MADV_MERGEABLE " (since Linux 2.6.32)" >> +Enable Kernel Samepage Merging (KSM) for the pages in the range specified by >> +.I addr >> +and >> +.IR len . >> +The KSM daemon >> +.RI ( ksmd ) >> +periodically scans those areas of user memory that have >> +been marked as mergeable, >> +looking for pages with identical content. > > I was rather puzzled by Andi calling that an internal implementation > detail. Okay, I suppose the "KSM daemon periodically scans" is an > internal implementation detail, though I think it helps to warn the > programmer of the overhead of MADV_MERGEABLE; but without "pages > with identical content", aren't we left mystified as to just what > this "merging" is all about? I agree. All I had changed was to remove mention of the KSM daemon -- I just say "the kernel". >> +These are replaced by a single write-protected page (which is automatically >> +copied if a process later wants to update the content of the page). >> +KSM only merges private anonymous pages (see >> +.BR mmap (2)). >> +The KSM feature is intended for applications that generate many >> +instances of the same data (e.g., virtualization systems such as KVM). >> +It can consume a lot of processing power; use with care. > > : > >> +See the kernel source file >> +.I Documentation/vm/ksm.txt >> +for more details. >> +The >> +.BR MADV_MERGEABLE >> +and >> +.BR MADV_UNMERGEABLE >> +operations are only available if the kernel was configured with >> +.BR CONFIG_KSM. >> +.TP >> +.BR MADV_UNMERGEABLE " (since Linux 2.6.32)" >> +Undo the effect of an earlier >> +.BR MADV_MERGEABLE >> +operation on the specified address range; >> +KSM unmerges whatever pages it had merged in the address rnage specified by > > range Thanks. >> +.IR addr >> +and >> +.IR length . >> .SH "RETURN VALUE" >> On success >> .BR madvise () >> @@ -189,6 +226,14 @@ is not a valid value >> .IP * >> The application is attempting to release locked or shared pages (with >> .BR MADV_DONTNEED ). >> +.IP * >> +.BR MADV_MERGEABLE >> +or >> +.BR MADV_UNMERGEABLE >> +was specified in >> +.IR advice , >> +but the kernel was not configured with >> +.BR CONFIG_KSM . >> .RE >> .TP >> .B EIO >> @@ -221,8 +266,10 @@ for file access. >> .BR MADV_REMOVE , >> .BR MADV_DONTFORK , >> .BR MADV_DOFORK , >> +.BR MAD_HWPOISON , > > Oh, I absolutely agree with you, MAD_HWPOISON indeed; > but Andi might prefer MADV_HWPOISON. > >> +.BR MADVISE_MERGEABLE, > > MADV_MERGEABLE, > >> and >> -.BR MAD_HWPOISON >> +.BR MADVISE_UNMERGEABLE > > MADV_UNMERGEABLE D'oh! All of the above fixed now. 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/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
