linux-kernel - man-pages text for MAV_MERGEABLE and MADV

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Message-ID: <AANLkTinX4TlNfvwrCtjfkU-bar3URnpvmPJB-sOi-9aT@mail.gmail.com>
Date:	Sat, 19 Jun 2010 10:47:13 +0200
From:	Michael Kerrisk <mtk.manpages@...il.com>
To:	hugh.dickins@...cali.co.uk, ieidus@...hat.com
Cc:	Andi Kleen <andi@...stfloor.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-man <linux-man@...r.kernel.org>
Subject: man-pages text for MAV_MERGEABLE and MADV_UNMERGEABLE

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.

Thanks to Andi and Andrew for pointers that this documentation was needed.

Thanks,

Michael


--- 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.
+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
+.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 ,
+.BR MADVISE_MERGEABLE ,
 and
-.BR MAD_HWPOISON
+.BR MADVISE_UNMERGEABLE
 are Linux-specific.
 .SH NOTES
 .SS "Linux Notes"
--
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