On Tue, Nov 19, 2019 at 12:01 AM Maciej S. Szmigiero <
mail@maciej.szmigiero.name> wrote:

> The compressed cache for swap pages (zswap) currently needs from 1 to 3
> extra kernel command line parameters in order to make it work: it has to be
> enabled by adding a "zswap.enabled=1" command line parameter and if one
> wants a different compressor or pool allocator than the default lzo / zbud
> combination then these choices also need to be specified on the kernel
> command line in additional parameters.
>
> Using a different compressor and allocator for zswap is actually pretty
> common as guides often recommend using the lz4 / z3fold pair instead of
> the default one.
> In such case it is also necessary to remember to enable the appropriate
> compression algorithm and pool allocator in the kernel config manually.
>
> Let's avoid the need for adding these kernel command line parameters and
> automatically pull in the dependencies for the selected compressor
> algorithm and pool allocator by adding an appropriate default switches to
> Kconfig.
>
> The default values for these options match what the code was using
> previously as its defaults.
>
> Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
>
Reviewed-by: Vitaly Wool <vitaly.wool@konsulko.com>

> ---
> Changes from v1:
> Rename CONFIG_ZSWAP_DEFAULT_COMP_* to CONFIG_ZSWAP_COMPRESSOR_DEFAULT_*
> and CONFIG_ZSWAP_DEFAULT_ZPOOL_* to CONFIG_ZSWAP_ZPOOL_DEFAULT_* while
> dropping the "_NAME" suffix from the final string option in both cases.
>
> Changes from v2:
> Add zsmalloc as a pool allocator choice, add a link to a page with
> benchmarks of various compression algorithms to the compression
> algorithm prompt option.
>
> Changes from v3:
> Update the zswap doc in Documentation, too.
>
> Changes from v4:
> Use IS_ENABLED() macro to initialize the zswap_enabled variable,
> make CONFIG_ZSWAP_COMPRESSOR_DEFAULT and CONFIG_ZSWAP_ZPOOL_DEFAULT
> depend on CONFIG_ZSWAP so they don't show in .config when zswap is
> deselected in Kconfig.
>
>  Documentation/vm/zswap.rst |  20 ++++---
>  mm/Kconfig                 | 118 ++++++++++++++++++++++++++++++++++++-
>  mm/zswap.c                 |  24 ++++----
>  3 files changed, 141 insertions(+), 21 deletions(-)
>
> diff --git a/Documentation/vm/zswap.rst b/Documentation/vm/zswap.rst
> index 1444ecd40911..2df6ee6b7a1d 100644
> --- a/Documentation/vm/zswap.rst
> +++ b/Documentation/vm/zswap.rst
> @@ -35,9 +35,11 @@ Zswap evicts pages from compressed cache on an LRU
> basis to the backing swap
>  device when the compressed pool reaches its size limit.  This requirement
> had
>  been identified in prior community discussions.
>
> -Zswap is disabled by default but can be enabled at boot time by setting
> -the ``enabled`` attribute to 1 at boot time. ie: ``zswap.enabled=1``.
> Zswap
> -can also be enabled and disabled at runtime using the sysfs interface.
> +Whether Zswap is enabled at the boot time depends on whether
> +the ``CONFIG_ZSWAP_DEFAULT_ON`` Kconfig option is enabled or not.
> +This setting can then be overridden by providing the kernel command line
> +``zswap.enabled=`` option, for example ``zswap.enabled=0``.
> +Zswap can also be enabled and disabled at runtime using the sysfs
> interface.
>  An example command to enable zswap at runtime, assuming sysfs is mounted
>  at ``/sys``, is::
>
> @@ -64,9 +66,10 @@ allocation in zpool is not directly accessible by
> address.  Rather, a handle is
>  returned by the allocation routine and that handle must be mapped before
> being
>  accessed.  The compressed memory pool grows on demand and shrinks as
> compressed
>  pages are freed.  The pool is not preallocated.  By default, a zpool
> -of type zbud is created, but it can be selected at boot time by
> -setting the ``zpool`` attribute, e.g. ``zswap.zpool=zbud``. It can
> -also be changed at runtime using the sysfs ``zpool`` attribute, e.g.::
> +of type selected in ``CONFIG_ZSWAP_ZPOOL_DEFAULT`` Kconfig option is
> created,
> +but it can be overridden at boot time by setting the ``zpool`` attribute,
> +e.g. ``zswap.zpool=zbud``. It can also be changed at runtime using the
> sysfs
> +``zpool`` attribute, e.g.::
>
>         echo zbud > /sys/module/zswap/parameters/zpool
>
> @@ -97,8 +100,9 @@ controlled policy:
>  * max_pool_percent - The maximum percentage of memory that the compressed
>    pool can occupy.
>
> -The default compressor is lzo, but it can be selected at boot time by
> -setting the ``compressor`` attribute, e.g. ``zswap.compressor=lzo``.
> +The default compressor is selected in ``CONFIG_ZSWAP_COMPRESSOR_DEFAULT``
> +Kconfig option, but it can be overridden at boot time by setting the
> +``compressor`` attribute, e.g. ``zswap.compressor=lzo``.
>  It can also be changed at runtime using the sysfs "compressor"
>  attribute, e.g.::
>
> diff --git a/mm/Kconfig b/mm/Kconfig
> index a5dae9a7eb51..ca71c4c2b048 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -525,7 +525,6 @@ config MEM_SOFT_DIRTY
>  config ZSWAP
>         bool "Compressed cache for swap pages (EXPERIMENTAL)"
>         depends on FRONTSWAP && CRYPTO=y
> -       select CRYPTO_LZO
>         select ZPOOL
>         help
>           A lightweight compressed cache for swap pages.  It takes
> @@ -541,6 +540,123 @@ config ZSWAP
>           they have not be fully explored on the large set of potential
>           configurations and workloads that exist.
>
> +choice
> +       prompt "Compressed cache for swap pages default compressor"
> +       depends on ZSWAP
> +       default ZSWAP_COMPRESSOR_DEFAULT_LZO
> +       help
> +         Selects the default compression algorithm for the compressed
> cache
> +         for swap pages.
> +
> +         For an overview what kind of performance can be expected from
> +         a particular compression algorithm please refer to the benchmarks
> +         available at the following LWN page:
> +         https://lwn.net/Articles/751795/
> +
> +         If in doubt, select 'LZO'.
> +
> +         The selection made here can be overridden by using the kernel
> +         command line 'zswap.compressor=' option.
> +
> +config ZSWAP_COMPRESSOR_DEFAULT_DEFLATE
> +       bool "Deflate"
> +       select CRYPTO_DEFLATE
> +       help
> +         Use the Deflate algorithm as the default compression algorithm.
> +
> +config ZSWAP_COMPRESSOR_DEFAULT_LZO
> +       bool "LZO"
> +       select CRYPTO_LZO
> +       help
> +         Use the LZO algorithm as the default compression algorithm.
> +
> +config ZSWAP_COMPRESSOR_DEFAULT_842
> +       bool "842"
> +       select CRYPTO_842
> +       help
> +         Use the 842 algorithm as the default compression algorithm.
> +
> +config ZSWAP_COMPRESSOR_DEFAULT_LZ4
> +       bool "LZ4"
> +       select CRYPTO_LZ4
> +       help
> +         Use the LZ4 algorithm as the default compression algorithm.
> +
> +config ZSWAP_COMPRESSOR_DEFAULT_LZ4HC
> +       bool "LZ4HC"
> +       select CRYPTO_LZ4HC
> +       help
> +         Use the LZ4HC algorithm as the default compression algorithm.
> +
> +config ZSWAP_COMPRESSOR_DEFAULT_ZSTD
> +       bool "zstd"
> +       select CRYPTO_ZSTD
> +       help
> +         Use the zstd algorithm as the default compression algorithm.
> +endchoice
> +
> +config ZSWAP_COMPRESSOR_DEFAULT
> +       string
> +       depends on ZSWAP
> +       default "deflate" if ZSWAP_COMPRESSOR_DEFAULT_DEFLATE
> +       default "lzo" if ZSWAP_COMPRESSOR_DEFAULT_LZO
> +       default "842" if ZSWAP_COMPRESSOR_DEFAULT_842
> +       default "lz4" if ZSWAP_COMPRESSOR_DEFAULT_LZ4
> +       default "lz4hc" if ZSWAP_COMPRESSOR_DEFAULT_LZ4HC
> +       default "zstd" if ZSWAP_COMPRESSOR_DEFAULT_ZSTD
> +       default ""
> +
> +choice
> +       prompt "Compressed cache for swap pages default allocator"
> +       depends on ZSWAP
> +       default ZSWAP_ZPOOL_DEFAULT_ZBUD
> +       help
> +         Selects the default allocator for the compressed cache for
> +         swap pages.
> +         The default is 'zbud' for compatibility, however please do
> +         read the description of each of the allocators below before
> +         making a right choice.
> +
> +         The selection made here can be overridden by using the kernel
> +         command line 'zswap.zpool=' option.
> +
> +config ZSWAP_ZPOOL_DEFAULT_ZBUD
> +       bool "zbud"
> +       select ZBUD
> +       help
> +         Use the zbud allocator as the default allocator.
> +
> +config ZSWAP_ZPOOL_DEFAULT_Z3FOLD
> +       bool "z3fold"
> +       select Z3FOLD
> +       help
> +         Use the z3fold allocator as the default allocator.
> +
> +config ZSWAP_ZPOOL_DEFAULT_ZSMALLOC
> +       bool "zsmalloc"
> +       select ZSMALLOC
> +       help
> +         Use the zsmalloc allocator as the default allocator.
> +endchoice
> +
> +config ZSWAP_ZPOOL_DEFAULT
> +       string
> +       depends on ZSWAP
> +       default "zbud" if ZSWAP_ZPOOL_DEFAULT_ZBUD
> +       default "z3fold" if ZSWAP_ZPOOL_DEFAULT_Z3FOLD
> +       default "zsmalloc" if ZSWAP_ZPOOL_DEFAULT_ZSMALLOC
> +       default ""
> +
> +config ZSWAP_DEFAULT_ON
> +       bool "Enable the compressed cache for swap pages by default"
> +       depends on ZSWAP
> +       help
> +         If selected, the compressed cache for swap pages will be enabled
> +         at boot, otherwise it will be disabled.
> +
> +         The selection made here can be overridden by using the kernel
> +         command line 'zswap.enabled=' option.
> +
>  config ZPOOL
>         tristate "Common API for compressed memory storage"
>         help
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 46a322316e52..1af303e88008 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -71,8 +71,8 @@ static u64 zswap_duplicate_entry;
>
>  #define ZSWAP_PARAM_UNSET ""
>
> -/* Enable/disable zswap (disabled by default) */
> -static bool zswap_enabled;
> +/* Enable/disable zswap */
> +static bool zswap_enabled = IS_ENABLED(CONFIG_ZSWAP_DEFAULT_ON);
>  static int zswap_enabled_param_set(const char *,
>                                    const struct kernel_param *);
>  static struct kernel_param_ops zswap_enabled_param_ops = {
> @@ -82,8 +82,7 @@ static struct kernel_param_ops zswap_enabled_param_ops =
> {
>  module_param_cb(enabled, &zswap_enabled_param_ops, &zswap_enabled, 0644);
>
>  /* Crypto compressor to use */
> -#define ZSWAP_COMPRESSOR_DEFAULT "lzo"
> -static char *zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
> +static char *zswap_compressor = CONFIG_ZSWAP_COMPRESSOR_DEFAULT;
>  static int zswap_compressor_param_set(const char *,
>                                       const struct kernel_param *);
>  static struct kernel_param_ops zswap_compressor_param_ops = {
> @@ -95,8 +94,7 @@ module_param_cb(compressor, &zswap_compressor_param_ops,
>                 &zswap_compressor, 0644);
>
>  /* Compressed storage zpool to use */
> -#define ZSWAP_ZPOOL_DEFAULT "zbud"
> -static char *zswap_zpool_type = ZSWAP_ZPOOL_DEFAULT;
> +static char *zswap_zpool_type = CONFIG_ZSWAP_ZPOOL_DEFAULT;
>  static int zswap_zpool_param_set(const char *, const struct kernel_param
> *);
>  static struct kernel_param_ops zswap_zpool_param_ops = {
>         .set =          zswap_zpool_param_set,
> @@ -569,11 +567,12 @@ static __init struct zswap_pool
> *__zswap_pool_create_fallback(void)
>         bool has_comp, has_zpool;
>
>         has_comp = crypto_has_comp(zswap_compressor, 0, 0);
> -       if (!has_comp && strcmp(zswap_compressor,
> ZSWAP_COMPRESSOR_DEFAULT)) {
> +       if (!has_comp && strcmp(zswap_compressor,
> +                               CONFIG_ZSWAP_COMPRESSOR_DEFAULT)) {
>                 pr_err("compressor %s not available, using default %s\n",
> -                      zswap_compressor, ZSWAP_COMPRESSOR_DEFAULT);
> +                      zswap_compressor, CONFIG_ZSWAP_COMPRESSOR_DEFAULT);
>                 param_free_charp(&zswap_compressor);
> -               zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
> +               zswap_compressor = CONFIG_ZSWAP_COMPRESSOR_DEFAULT;
>                 has_comp = crypto_has_comp(zswap_compressor, 0, 0);
>         }
>         if (!has_comp) {
> @@ -584,11 +583,12 @@ static __init struct zswap_pool
> *__zswap_pool_create_fallback(void)
>         }
>
>         has_zpool = zpool_has_pool(zswap_zpool_type);
> -       if (!has_zpool && strcmp(zswap_zpool_type, ZSWAP_ZPOOL_DEFAULT)) {
> +       if (!has_zpool && strcmp(zswap_zpool_type,
> +                                CONFIG_ZSWAP_ZPOOL_DEFAULT)) {
>                 pr_err("zpool %s not available, using default %s\n",
> -                      zswap_zpool_type, ZSWAP_ZPOOL_DEFAULT);
> +                      zswap_zpool_type, CONFIG_ZSWAP_ZPOOL_DEFAULT);
>                 param_free_charp(&zswap_zpool_type);
> -               zswap_zpool_type = ZSWAP_ZPOOL_DEFAULT;
> +               zswap_zpool_type = CONFIG_ZSWAP_ZPOOL_DEFAULT;
>                 has_zpool = zpool_has_pool(zswap_zpool_type);
>         }
>         if (!has_zpool) {
>