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Date:   Thu, 29 Oct 2020 03:59:27 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To:     Minchan Kim <minchan@kernel.org>,
        Rui Salvaterra <rsalvaterra@gmail.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>, ngupta@vflare.org,
        sergey.senozhatsky.work@gmail.com, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4] zram: break the strict dependency from lzo
Message-ID: <20201028185927.GB128655@google.com>
References: <20201028115921.848-1-rsalvaterra@gmail.com>
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Cc-ing Andrew

message-id: 20201028115921.848-1-rsalvaterra@gmail.com

On (20/10/28 11:59), Rui Salvaterra wrote:
> There's nothing special about zram and lzo. It works just fine without it, so
> as long as at least one of the other supported compression algorithms is
> selected.
> 
> Suggested-by: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
> Signed-off-by: Rui Salvaterra <rsalvaterra@gmail.com>

Minchan, I'm fine with the change.

Two things from my side:

1) The commit message, probably, can be a bit more informative. Something
like this?

	ZRAM always enables CRYPTO_LZO because lzo-rle is the hardcoded
	fallback compression algorithm, which means that on systems where
	ZRAM always use, for instance, CRYPTO_ZSTD lzo kernel module
	becomes unneeded. This patch removes the hardcoded lzo-lre
	dependency, instead ZRAM picks the first supported CRYPTO
	compression algorithm, should it be ZSTD or LZ4, etc; and only
	forcibly enables CRYPTO_LZO (previous behaviour) if none of the
	alternative algorithms were selected.


2) The ZRAM_AUTOSEL_ALGO allows to deselect CRYPTO_LZO only if
CRYPTO_LZ4/CRYPTO_LZ4HC/CRYPTO_842/CRYPTO_ZSTD are compiled in (=y).
If any of the algorithms is selected as a module (=m) then CRYPTO_LZO
is selected as the default algorithm. Apparently depends on !(CONFIG_FOO)
means depends on !(CONFIG_FOO=y).

It appears that the below change fixes it, but it looks a bit ugly.

---
diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig
index 141ce0ebad06..f2fd34de9200 100644
--- a/drivers/block/zram/Kconfig
+++ b/drivers/block/zram/Kconfig
@@ -15,7 +15,7 @@ config ZRAM
 
 config ZRAM_AUTOSEL_ALGO
 	def_bool y
-	depends on ZRAM && !(CRYPTO_LZ4 || CRYPTO_LZ4HC || CRYPTO_842 || CRYPTO_ZSTD)
+	depends on ZRAM && !(CRYPTO_LZ4=m || CRYPTO_LZ4HC=m || CRYPTO_842=m || CRYPTO_ZSTD=m || CRYPTO_LZ4=y || CRYPTO_LZ4HC=y || CRYPTO_842=y || CRYPTO_ZSTD=y)
 	select CRYPTO_LZO
 
 config ZRAM_WRITEBACK
---

	-ss