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

Minchan Kim
2020-11-19T22:26:36Z

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