Please re-enable LZ4 in 4.9 kernel config

[RadekHvizdos]

Hi all,

I was using LZ4 compression for memory compression. This has stopped working after kernel upgrade to 4.9 because the functionality is no longer present:

diff 4.4.txt 4.9.txt
4d3
< CONFIG_ZRAM_LZ4_COMPRESS=y
8d6
< CONFIG_LZ4_COMPRESS=m

Please re-enable these options.

Thank you.

[ED6E0F17]

The required option is:

config CRYPTO_LZ4
	tristate "LZ4 compression algorithm"
	select CRYPTO_ALGAPI
	select LZ4_COMPRESS
	select LZ4_DECOMPRESS
	help
	  This is the LZ4 algorithm.

It would be good to have this in the kernel.

[pelwell]

Yes, it appears that as of 4.8 the ZRAM module uses the compression functions provided by the crypto module, and enabling CRYPTO_LZ4 just causes two small modules to be built:

-rw-rw-r-- 1 phil phil 6199 Mar  7 16:00 ./lib/lz4/lz4_compress.ko
-rw-rw-r-- 1 phil phil 5879 Mar  7 16:00 ./crypto/lz4.ko

@popcornmix Shall I add this config option?

[RadekHvizdos]

@pelwell, @ED6E0F17 are you sure we don't need ZRAM_LZ4_COMPRESS=y as well?

Thanks for looking into this.

[pelwell]

defconfigs should only include the absolute minimum number of settings required to achieve a given configuration - any defaults, or settings which are implied by others, are omitted. Fortunately the savedefconfig make rule takes care of the pruning for us.

In this case, as @ED6E0F17's post above shows, setting CRYPTO_LZ4 automatically selects LZ4_COMPRESS, so it shouldn't appear in the defconfig.

[popcornmix]

@pelwell no objections.