linux-kernel - [PATCH v3 1/1] mm/ksm: documentation for coloured zero pages deduplication

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Date:   Fri, 20 Jan 2017 16:52:02 +0100
From:   Claudio Imbrenda <imbrenda@...ux.vnet.ibm.com>
To:     linux-mm@...ck.org
Cc:     borntraeger@...ibm.com, hughd@...gle.com, aarcange@...hat.com,
        chrisw@...s-sol.org, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3 1/1] mm/ksm: documentation for coloured zero pages deduplication

This patch adds the needed documentation for the use_zero_pages property.

Signed-off-by: Claudio Imbrenda <imbrenda@...ux.vnet.ibm.com>
---
 Documentation/vm/ksm.txt | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/Documentation/vm/ksm.txt b/Documentation/vm/ksm.txt
index f34a8ee..0c64a81d 100644
--- a/Documentation/vm/ksm.txt
+++ b/Documentation/vm/ksm.txt
@@ -80,6 +80,20 @@ run              - set 0 to stop ksmd from running but keep merged pages,
                    Default: 0 (must be changed to 1 to activate KSM,
                                except if CONFIG_SYSFS is disabled)
 
+use_zero_pages   - specifies whether empty pages (i.e. allocated pages
+                   that only contain zeroes) should be treated specially.
+                   When set to 1, empty pages are merged with the kernel
+                   zero page(s) instead of with each other as it would
+                   happen normally. This can improve the performance on
+                   architectures with coloured zero pages, depending on
+                   the workload. Care should be taken when enabling this
+                   setting, as it can potentially degrade the performance
+                   of KSM for some workloads, for example if the checksums
+                   of pages candidate for merging match the checksum of
+                   an empty page. This setting can be changed at any time,
+                   it is only effective for pages merged after the change.
+                   Default: 0 (normal KSM behaviour as in earlier releases)
+
 The effectiveness of KSM and MADV_MERGEABLE is shown in /sys/kernel/mm/ksm/:
 
 pages_shared     - how many shared pages are being used
-- 
1.9.1