linux-kernel - [PATCH v4] zram: break the strict dependency from lzo

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Date:   Wed, 28 Oct 2020 11:59:21 +0000
From:   Rui Salvaterra <rsalvaterra@...il.com>
To:     minchan@...nel.org, ngupta@...are.org,
        sergey.senozhatsky.work@...il.com
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Rui Salvaterra <rsalvaterra@...il.com>
Subject: [PATCH v4] zram: break the strict dependency from lzo

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@...il.com>
Signed-off-by: Rui Salvaterra <rsalvaterra@...il.com>
---
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.

 drivers/block/zram/Kconfig    |  6 +++++-
 drivers/block/zram/zcomp.c    | 17 +++++++++++++++++
 drivers/block/zram/zcomp.h    |  1 +
 drivers/block/zram/zram_drv.c |  5 +++--
 4 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig
index fe7a4b7d30cf..141ce0ebad06 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 +13,11 @@ config ZRAM
 
 	  See Documentation/admin-guide/blockdev/zram.rst for more information.
 
+config ZRAM_AUTOSEL_ALGO
+	def_bool y
+	depends on ZRAM && !(CRYPTO_LZ4 || CRYPTO_LZ4HC || CRYPTO_842 || CRYPTO_ZSTD)
+	select CRYPTO_LZO
+
 config ZRAM_WRITEBACK
        bool "Write back incompressible or idle page to backing device"
        depends on ZRAM
diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
index 33e3b76c4fa9..4fad177c78c4 100644
--- a/drivers/block/zram/zcomp.c
+++ b/drivers/block/zram/zcomp.c
@@ -15,8 +15,10 @@
 #include "zcomp.h"
 
 static const char * const backends[] = {
+#if IS_ENABLED(CONFIG_CRYPTO_LZO)
 	"lzo",
 	"lzo-rle",
+#endif
 #if IS_ENABLED(CONFIG_CRYPTO_LZ4)
 	"lz4",
 #endif
@@ -202,6 +204,21 @@ void zcomp_destroy(struct zcomp *comp)
 	kfree(comp);
 }
 
+const char *default_compressor(void)
+{
+	/*
+	 * Pick the first available one (there should be at least one).
+	 *
+	 * In theory, we can drop all the ifdefs from backends[] and
+	 * just iterate backends array doing crypto_has_comp(comp, 0, 0)
+	 * for each entry and return the first one which is recognized by
+	 * crypto. But crypto_has_comp() modprobes compression drivers,
+	 * so we may end up with extra loaded drivers, when the 'default'
+	 * compressor is not what zram is configured to use.
+	 */
+	return backends[0];
+}
+
 /*
  * search available compressors for requested algorithm.
  * allocate new zcomp and initialize it. return compressing
diff --git a/drivers/block/zram/zcomp.h b/drivers/block/zram/zcomp.h
index 40f6420f4b2e..f104be9eae9c 100644
--- a/drivers/block/zram/zcomp.h
+++ b/drivers/block/zram/zcomp.h
@@ -27,6 +27,7 @@ int zcomp_cpu_dead(unsigned int cpu, struct hlist_node *node);
 ssize_t zcomp_available_show(const char *comp, char *buf);
 bool zcomp_available_algorithm(const char *comp);
 
+const char *default_compressor(void);
 struct zcomp *zcomp_create(const char *comp);
 void zcomp_destroy(struct zcomp *comp);
 
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 1b697208d661..f02ee050c7bf 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -42,7 +42,6 @@ static DEFINE_IDR(zram_index_idr);
 static DEFINE_MUTEX(zram_index_mutex);
 
 static int zram_major;
-static const char *default_compressor = "lzo-rle";
 
 /* Module params (documentation at end) */
 static unsigned int num_devices = 1;
@@ -1960,7 +1959,9 @@ static int zram_add(void)
 	blk_queue_flag_set(QUEUE_FLAG_STABLE_WRITES, zram->disk->queue);
 	device_add_disk(NULL, zram->disk, zram_disk_attr_groups);
 
-	strlcpy(zram->compressor, default_compressor, sizeof(zram->compressor));
+	strlcpy(zram->compressor,
+		default_compressor(),
+		sizeof(zram->compressor));
 
 	zram_debugfs_register(zram);
 	pr_info("Added device: %s\n", zram->disk->disk_name);
-- 
2.29.1