From: Srividya Desireddy <[email protected]>
Date: Wed, 6 Dec 2017 16:29:50 +0530
Subject: [PATCH v2] zswap: Update with same-value filled page feature
Changes since v1:
Updated to clarify about zswap.same_filled_pages_enabled parameter.
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 <[email protected]>
---
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..0b3a114 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 remain stored
+unchanged in zswap until they are either 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
On Wed, Dec 6, 2017 at 6:48 AM, Srividya Desireddy
<[email protected]> wrote:
> From: Srividya Desireddy <[email protected]>
> Date: Wed, 6 Dec 2017 16:29:50 +0530
> Subject: [PATCH v2] zswap: Update with same-value filled page feature
>
> Changes since v1:
> Updated to clarify about zswap.same_filled_pages_enabled parameter.
>
> 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 <[email protected]>
Acked-by: Dan Streetman <[email protected]>
> ---
> 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..0b3a114 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 remain stored
> +unchanged in zswap until they are either 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
>