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-rw-r--r--Documentation/vm/zswap.rst13
1 files changed, 13 insertions, 0 deletions
diff --git a/Documentation/vm/zswap.rst b/Documentation/vm/zswap.rst
index 1444ecd40911..61f6185188cd 100644
--- a/Documentation/vm/zswap.rst
+++ b/Documentation/vm/zswap.rst
@@ -130,6 +130,19 @@ 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.
+To prevent zswap from shrinking pool when zswap is full and there's a high
+pressure on swap (this will result in flipping pages in and out zswap pool
+without any real benefit but with a performance drop for the system), a
+special parameter has been introduced to implement a sort of hysteresis to
+refuse taking pages into zswap pool until it has sufficient space if the limit
+has been hit. To set the threshold at which zswap would start accepting pages
+again after it became full, use the sysfs ``accept_threhsold_percent``
+attribute, e. g.::
+
+ echo 80 > /sys/module/zswap/parameters/accept_threhsold_percent
+
+Setting this parameter to 100 will disable the hysteresis.
+
A debugfs interface is provided for various statistic about pool size, number
of pages stored, same-value filled pages and various counters for the reasons
pages are rejected.