Re: [PATCH v5] zram: break the strict dependency from lzo

[Minchan Kim <minchan@kernel.org>]

On Sun, Nov 15, 2020 at 10:15:14AM +0000, Rui Salvaterra wrote:
> From the beginning, the zram block device always enabled CRYPTO_LZO, since
> lzo-rle is hardcoded as the fallback compression algorithm. As a consequence, on
> systems where another compression algorithm is chosen (e.g. CRYPTO_ZSTD), the
> lzo kernel module becomes unused, while still having to be built/loaded.
> 
> This patch removes the hardcoded lzo-rle dependency and allows the user to
> select the default compression algorithm for zram at build time. The previous
> behaviour is kept, as the default algorithm is still lzo-rle.
> 
> Suggested-by: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
> Suggested-by: Minchan Kim <minchan@kernel.org>
> Signed-off-by: Rui Salvaterra <rsalvaterra@gmail.com>
> ---
> v5: incorporate Minchan's feedback. Allow the user to choose a default algorithm.
> v4: incorporate Sergey's feedback and fix a small typo.
> v3: fix the default selection when lzo isn't present. Rebase against 5.10-rc1.
> v2: fix the dependency on CRYPTO.
> 
> I believe this is the final version, but it does deserve some comment. Given the
> choice of having more preprocessor #if/#endif directives in C files or making
> the kconfig a bit more complex, I went for the latter. However, since kconfig
> choices can only be boolean, I had to devise a way to make a string selection
> based on the boolean choice, hence the ZRAM_DEF_COMP symbol.
> I also tried to make the ZRAM_AUTOSEL_ALGO definition a bit less painful to the
> eye, while still allowing for the compression algorithms to be selected as
> modules, as per Sergey's suggestion.
> 
>  drivers/block/zram/Kconfig    | 49 ++++++++++++++++++++++++++++++++++-
>  drivers/block/zram/zcomp.c    |  2 ++
>  drivers/block/zram/zram_drv.c |  2 +-
>  3 files changed, 51 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig
> index fe7a4b7d30cf..cde089c30ffb 100644
> --- a/drivers/block/zram/Kconfig
> +++ b/drivers/block/zram/Kconfig
> @@ -2,7 +2,6 @@
>  config ZRAM
>  	tristate "Compressed RAM block device support"
>  	depends on BLOCK && SYSFS && ZSMALLOC && CRYPTO
> -	select CRYPTO_LZO
>  	help
>  	  Creates virtual block devices called /dev/zramX (X = 0, 1, ...).
>  	  Pages written to these disks are compressed and stored in memory
> @@ -14,6 +13,54 @@ config ZRAM
>  
>  	  See Documentation/admin-guide/blockdev/zram.rst for more information.
>  
> +choice
> +	prompt "Default zram compression algorithm"
> +	depends on ZRAM
> +
> +config ZRAM_DEF_COMP_LZORLE
> +	bool "lzo-rle"
> +	depends on CRYPTO_LZO
> +
> +config ZRAM_DEF_COMP_ZSTD
> +	bool "zstd"
> +	depends on CRYPTO_ZSTD
> +
> +config ZRAM_DEF_COMP_LZ4
> +	bool "lz4"
> +	depends on CRYPTO_LZ4
> +
> +config ZRAM_DEF_COMP_LZO
> +	bool "lzo"
> +	depends on CRYPTO_LZO
> +
> +config ZRAM_DEF_COMP_LZ4HC
> +	bool "lz4hc"
> +	depends on CRYPTO_LZ4HC
> +
> +config ZRAM_DEF_COMP_842
> +	bool "842"
> +	depends on CRYPTO_842
> +
> +endchoice
> +
> +config ZRAM_DEF_COMP
> +	string
> +	default "lzo-rle" if ZRAM_DEF_COMP_LZORLE
> +	default "zstd" if ZRAM_DEF_COMP_ZSTD
> +	default "lz4" if ZRAM_DEF_COMP_LZ4
> +	default "lzo" if ZRAM_DEF_COMP_LZO
> +	default "lz4hc" if ZRAM_DEF_COMP_LZ4HC
> +	default "842" if ZRAM_DEF_COMP_842
> +
> +config ZRAM_AUTOSEL_ALGO
> +	def_bool y
> +	depends on ZRAM && \
> +		!(CRYPTO_LZ4=m   || CRYPTO_LZ4=y   || \
> +		  CRYPTO_LZ4HC=m || CRYPTO_LZ4HC=y || \
> +		  CRYPTO_842=m   || CRYPTO_842=y   || \
> +		  CRYPTO_ZSTD=m  || CRYPTO_ZSTD=y)
> +	select CRYPTO_LZO
> +

Hi Rui,

What's the purpose of ZRAM_AUTOSEL_ALGO?
If you and Sergey already discussed, sorry about the missing it.

Below doesn't work for your goal?

diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig
index fe7a4b7d30cf..7f3c50f5f87e 100644
--- a/drivers/block/zram/Kconfig
+++ b/drivers/block/zram/Kconfig
@@ -2,7 +2,6 @@
 config ZRAM
        tristate "Compressed RAM block device support"
        depends on BLOCK && SYSFS && ZSMALLOC && CRYPTO
-       select CRYPTO_LZO
        help
          Creates virtual block devices called /dev/zramX (X = 0, 1, ...).
          Pages written to these disks are compressed and stored in memory
@@ -14,6 +13,32 @@ config ZRAM

          See Documentation/admin-guide/blockdev/zram.rst for more information.

+
+choice
+       prompt "zram default compressor"
+       default ZRAM_COMP_LZO_DEF
+       depends on ZRAM || CRYPTO_LZ4
+       help
+         a
+
+config ZRAM_COMP_LZO_DEF
+       bool "lzo"
+       select CRYPTO_LZO
+       help
+         b
+
+config ZRAM_COMP_LZ4_DEF
+       bool "lz4"
+       depends on CRYPTO_LZ4
+       help
+         c
+endchoice
+
+config ZRAM_DEF_COMP
+       string
+       default "lzo" if ZRAM_COMP_LZO_DEF
+       default "lz4" if ZRAM_COMP_LZ4_DEF