linux-kernel - [PATCH 4/4] zswap: Update document with sharing of duplicate pages feature

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Date:	Wed, 17 Aug 2016 10:20:19 +0000
From:	Srividya Desireddy <srividya.dr@...sung.com>
To:	sjenning@...hat.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, corbet@....net,
	akpm@...ux-foundation.org, ddstreet@...e.org,
	linux-doc@...r.kernel.org
Cc:	Srividya Desireddy <srividya.dr@...sung.com>,
	Dinakar Reddy Pathireddy 
	<dinakar.p@...sung.com>,
	샤란 <sharan.allur@...sung.com>,
	SUNEEL KUMAR SURIMANI <suneel@...sung.com>,
	김주훈 <juhunkim@...sung.com>
Subject: [PATCH 4/4] zswap: Update document with sharing of duplicate pages feature

From: Srividya Desireddy <srividya.dr@...sung.com>
Date: Wed, 17 Aug 2016 14:34:41 +0530
Subject: [PATCH 4/4] zswap: Update document with sharing of duplicate pages
 feature

Updated zswap document with details on the sharing of duplicate swap pages
feature. The usage of zswap.same_page_sharing module parameter is
explained.

Signed-off-by: Srividya Desireddy <srividya.dr@...sung.com>
---
 Documentation/vm/zswap.txt |   18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/Documentation/vm/zswap.txt b/Documentation/vm/zswap.txt
index 89fff7d..cf11807 100644
--- a/Documentation/vm/zswap.txt
+++ b/Documentation/vm/zswap.txt
@@ -98,5 +98,23 @@ request is made for a page in an old zpool, it is uncompressed using its
 original compressor.  Once all pages are removed from an old zpool, the zpool
 and its compressor are freed.
 
+Some of the pages swapped to zswap have same content as that of pages already
+stored in zswap. These pages are compressed and stored in the zpool memory.
+Same page sharing feature enables the duplicate pages to share same compressed
+zpool memory. This helps in reducing the zpool memory allocated by zswap to
+store compressed pages.
+
+Same page sharing feature is disabled by default and can be enabled at boot
+time by setting the "same_page_sharing" attribute to 1 at boot time. ie:
+zswap.same_page_sharing=1. It can also be enabled and disabled at runtime
+using the sysfs "same_page_sharing" attribute, e.g.
+
+echo 1 > /sys/module/zswap/parameters/same_page_sharing
+
+When zswap same page sharing is disabled at runtime it will stop sharing the
+new duplicate pages that are being swapped out. However, the existing duplicate
+pages will keep sharing the compressed memory pool until they are swapped in or
+invalidated.
+
 A debugfs interface is provided for various statistic about pool size, number
 of pages stored, and various counters for the reasons pages are rejected.
-- 
1.7.9.5