From: Srividya Desireddy <srividya.dr@xxxxxxxxxxx> 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@xxxxxxxxxxx> --- 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
