[PATCH] zswap: Update with same-value filled page feature

From: Srividya Desireddy <srividya.dr@samsung.com>
To: Dan Streetman <ddstreet@ieee.org>,
	"sjenning@redhat.com" <sjenning@redhat.com>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Cc: Dinakar Reddy Pathireddy <dinakar.p@samsung.com>,
	RAJIB BASU <rajib.basu@samsung.com>,
	Srikanth Mandalapu <srikanth.m@samsung.com>,
	SHARAN ALLUR <sharan.allur@samsung.com>,
	JUHUN KIM <juhunkim@samsung.com>,
	Srividya Desireddy <srividya.dr@samsung.com>,
	"srividya.desireddy@gmail.com" <srividya.desireddy@gmail.com>
Subject: [PATCH] zswap: Update with same-value filled page feature
Date: Wed, 29 Nov 2017 15:34:37 +0000	[thread overview]
Message-ID: <20171129153437epcms5p64b04efa370cc42bb0f9e5677e298704e@epcms5p6> (raw)
In-Reply-To: <CALZtONA1R8HyODqUP8Z-0yxvRAsV=Zo8OD2PQT3HwWWmqE6Hig@mail.gmail.com>

From: Srividya Desireddy <srividya.dr@samsung.com>
Date: Wed, 29 Nov 2017 20:23:15 +0530
Subject: [PATCH] zswap: Update with same-value filled page feature

Updated zswap document with details on same-value filled
pages identification feature.
The usage of zswap.same_filled_pages_enabled module parameter
is explained.

Signed-off-by: Srividya Desireddy <srividya.dr@samsung.com>
---
 Documentation/vm/zswap.txt | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/Documentation/vm/zswap.txt b/Documentation/vm/zswap.txt
index 89fff7d..cc015b5 100644
--- a/Documentation/vm/zswap.txt
+++ b/Documentation/vm/zswap.txt
@@ -98,5 +98,25 @@ 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 in zswap are same-value filled pages (i.e. contents of the
+page have same value or repetitive pattern). These pages include zero-filled
+pages and they are handled differently. During store operation, a page is
+checked if it is a same-value filled page before compressing it. If true, the
+compressed length of the page is set to zero and the pattern or same-filled
+value is stored.
+
+Same-value filled pages identification feature is enabled by default and can be
+disabled at boot time by setting the "same_filled_pages_enabled" attribute to 0,
+e.g. zswap.same_filled_pages_enabled=0. It can also be enabled and disabled at
+runtime using the sysfs "same_filled_pages_enabled" attribute, e.g.
+
+echo 1 > /sys/module/zswap/parameters/same_filled_pages_enabled
+
+When zswap same-filled page identification is disabled at runtime, it will stop
+checking for the same-value filled pages during store operation. However, the
+existing pages which are marked as same-value filled pages will be loaded 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.
+of pages stored, same-value filled pages and various counters for the reasons
+pages are rejected.
-- 
2.7.4

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