From: Srividya Desireddy <srividya.dr@xxxxxxxxxxx> Subject: 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@xxxxxxxxxxx> Acked-by: Dan Streetman <ddstreet@xxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- Documentation/vm/zswap.txt | 22 +++++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-) diff -puN Documentation/vm/zswap.txt~zswap-update-with-same-value-filled-page-feature Documentation/vm/zswap.txt --- a/Documentation/vm/zswap.txt~zswap-update-with-same-value-filled-page-feature +++ a/Documentation/vm/zswap.txt @@ -98,5 +98,25 @@ request is made for a page in an old zpo 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. _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
