Re: [PATCH 3/4] mm: Kconfig: simplify zswap configuration

From: Vlastimil Babka
Date: Tue Aug 24 2021 - 08:05:04 EST


+CC zswap maintainers

On 8/19/21 21:55, Johannes Weiner wrote:
> Clean up option ordering; make prompts and help text more concise and
> actionable for non-developers; turn depends into selects where
> possible, so that users can simply select the functionality they want
> without having to chase down obscure code dependencies.
>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> ---
> drivers/block/zram/Kconfig | 3 ++-
> mm/Kconfig | 53 ++++++++++++++++++--------------------
> 2 files changed, 27 insertions(+), 29 deletions(-)
>
> diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig
> index 668c6bf2554d..e4163d4b936b 100644
> --- a/drivers/block/zram/Kconfig
> +++ b/drivers/block/zram/Kconfig
> @@ -1,8 +1,9 @@
> # SPDX-License-Identifier: GPL-2.0
> config ZRAM
> tristate "Compressed RAM block device support"
> - depends on BLOCK && SYSFS && ZSMALLOC && CRYPTO
> + depends on BLOCK && SYSFS
> depends on CRYPTO_LZO || CRYPTO_ZSTD || CRYPTO_LZ4 || CRYPTO_LZ4HC || CRYPTO_842
> + select ZSMALLOC
> help
> Creates virtual block devices called /dev/zramX (X = 0, 1, ...).
> Pages written to these disks are compressed and stored in memory
> diff --git a/mm/Kconfig b/mm/Kconfig
> index dbceaa2a04a4..62c6e6092a0a 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -21,9 +21,13 @@ menuconfig SWAP
>
> if SWAP
>
> +config ZPOOL
> + bool
> +
> config ZSWAP
> bool "Compressed cache for swap pages (EXPERIMENTAL)"
> - depends on FRONTSWAP && CRYPTO=y
> + select FRONTSWAP
> + select CRYPTO
> select ZPOOL
> help
> A lightweight compressed cache for swap pages. It takes
> @@ -39,8 +43,18 @@ config ZSWAP
> they have not be fully explored on the large set of potential
> configurations and workloads that exist.
>
> +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.
> +
> choice
> - prompt "Compressed cache for swap pages default compressor"
> + prompt "Default compressor"
> depends on ZSWAP
> default ZSWAP_COMPRESSOR_DEFAULT_LZO
> help
> @@ -106,7 +120,7 @@ config ZSWAP_COMPRESSOR_DEFAULT
> default ""
>
> choice
> - prompt "Compressed cache for swap pages default allocator"
> + prompt "Default allocator"
> depends on ZSWAP
> default ZSWAP_ZPOOL_DEFAULT_ZBUD
> help
> @@ -146,24 +160,9 @@ config ZSWAP_ZPOOL_DEFAULT
> 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
> - Compressed memory storage API. This allows using either zbud or
> - zsmalloc.
> -
> config ZBUD
> - tristate "Low (Up to 2x) density storage for compressed pages"
> + tristate "2:1 compression allocator (zbud)"
> + depends on ZSWAP
> help
> A special purpose allocator for storing compressed pages.
> It is designed to store up to two compressed pages per physical
> @@ -172,8 +171,8 @@ config ZBUD
> density approach when reclaim will be used.
>
> config Z3FOLD
> - tristate "Up to 3x density storage for compressed pages"
> - depends on ZPOOL
> + tristate "3:1 compression allocator (z3fold)"
> + depends on ZSWAP
> help
> A special purpose allocator for storing compressed pages.
> It is designed to store up to three compressed pages per physical
> @@ -181,15 +180,13 @@ config Z3FOLD
> still there.
>
> config ZSMALLOC
> - tristate "Memory allocator for compressed pages"
> + tristate
> + prompt "N:1 compression allocator (zsmalloc)" if ZSWAP
> depends on MMU
> help
> zsmalloc is a slab-based memory allocator designed to store
> - compressed RAM pages. zsmalloc uses virtual memory mapping
> - in order to reduce fragmentation. However, this results in a
> - non-standard allocator interface where a handle, not a pointer, is
> - returned by an alloc(). This handle must be mapped in order to
> - access the allocated space.
> + pages of various compression levels efficiently. It achieves
> + the highest storage density with the least amount of fragmentation.
>
> config ZSMALLOC_STAT
> bool "Export zsmalloc statistics"
>