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Documentation/vm/zswap.txt: update with same-value filled page feature 

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

Link: http://lkml.kernel.org/r/20171206114852epcms5p6973b02a9f455d5d3c765eafda0fe2631@epcms5p6
Signed-off-by: Srividya Desireddy <srividya.dr@samsung.com>
Acked-by: Dan Streetman <ddstreet@ieee.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Srividya Desireddy 2017-12-14 15:32:45 -08:00 committed by Linus Torvalds
parent 3756f6401c
commit 51f73fffbf
1 changed files with 21 additions and 1 deletions
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Documentation/vm/zswap.txt
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@ -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.