[PATCH 1/2] proc.5: Explain /proc/sys/vm/compact_memory

[Elie De Brauwer <eliedebrauwer-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Since 2.6.36 [1] CONFIG_COMPACTION is supported in Linux (for a
detailed explanation see [2]). But in essence the contents of /proc/buddyinfo
shows how much contiguous areas of a certain size are available. These
numbers are not actually up to date as the Linux kernel will implicitely
trigger compaction (+- defragmentation) when an allocation is done.
This makes it difficult since you can't predict upfront whether or not a
large allocation will succeed or not.
By using /proc/sys/vm/compact_memory you can explicitely trigger compaction
to occur and /proc/buddyinfo will give a more realistic view on the
available memory in contiguous areas.

This patch updates proc.5 to explain the usage of this file and is
inspired upon Documentation/systcl/vm.txt [3]

[1] http://kernelnewbies.org/Linux_2_6_35#head-9cb0a1275559d40296da42efb7977896ac9edab7
[2] http://lwn.net/Articles/368869/
[3] http://lxr.free-electrons.com/source/Documentation/sysctl/vm.txt#L100

Signed-off-by: Elie De Brauwer <eliedebrauwer-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
 man5/proc.5 | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/man5/proc.5 b/man5/proc.5
index 860eb66..5bff2a0 100644
--- a/man5/proc.5
+++ b/man5/proc.5
@@ -3943,6 +3943,15 @@ On some systems, it is not present.
 This directory contains files for memory management tuning, buffer and
 cache management.
 .TP
+.IR /proc/sys/vm/compact_memory " (since Linux 2.6.35)"
+When 1 is written to this file, all zones are compacted such that free
+memory is available in contiguous blocks where possible.
+The effect of this action can be seen by examining
+.IR /proc/buddyinfo .
+.IP
+Only present if the kernel was configured with
+.BR CONFIG_COMPACTION .
+.TP
 .IR /proc/sys/vm/drop_caches " (since Linux 2.6.16)"
 Writing to this file causes the kernel to drop clean caches, dentries, and
 inodes from memory, causing that memory to become free.
-- 
2.1.4

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