Re: [PATCH v2] zswap: Update with same-value filled page feature

[Dan Streetman]

On Wed, Dec 6, 2017 at 6:48 AM, Srividya Desireddy
<srividya.dr@xxxxxxxxxxx> wrote:
> From: Srividya Desireddy <srividya.dr@xxxxxxxxxxx>
> 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 <srividya.dr@xxxxxxxxxxx>

Acked-by: Dan Streetman <ddstreet@xxxxxxxx>

> ---
>  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
>