admin-guide/mm/zswap.rst

9 in the process of being swapped out and attempts to compress them into a
10 dynamically allocated RAM-based memory pool.  zswap basically trades CPU cycles
11 for potentially reduced swap I/O.  This trade-off can also result in a
24   drastically reducing life-shortening writes.
31 the ``CONFIG_ZSWAP_DEFAULT_ON`` Kconfig option is enabled or not.
41 being swapped out.  However, it will _not_ immediately write out or fault
46 fault back into memory all swapped out pages, including those in the
57 allocation in zpool is not directly accessible by address.  Rather, a handle is
60 pages are freed.  The pool is not preallocated.  By default, a zpool
69 means the compression ratio will always be 2:1 or worse (because of half-full
76 with a red-black tree per swap type.  The swap offset is the search key for the
90 * max_pool_percent - The maximum percentage of memory that the compressed
102 compressed pages are not modified; they are left in their own zpool.  When a
107 Some of the pages in zswap are same-value filled pages (i.e. contents of the
108 page have same value or repetitive pattern). These pages include zero-filled
110 checked if it is a same-value filled page before compressing it. If true, the
111 compressed length of the page is set to zero and the pattern or same-filled
114 Same-value filled pages identification feature is enabled by default and can be
122 When zswap same-filled page identification is disabled at runtime, it will stop
123 checking for the same-value filled pages during store operation.
124 In other words, every page will be then considered non-same-value filled.
125 However, the existing pages which are marked as same-value filled pages remain
129 ability to efficiently store same-filled pages without enabling the whole
131 In this case the handling of non-same-value pages by zswap (enabled by default)
157 of pages stored, same-value filled pages and various counters for the reasons