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From:   Johannes Weiner <hannes@cmpxchg.org>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        kernel-team@fb.com
Subject: [PATCH 3/4] mm: Kconfig: simplify zswap configuration
Date:   Thu, 19 Aug 2021 15:55:32 -0400
Message-Id: <20210819195533.211756-3-hannes@cmpxchg.org>
In-Reply-To: <20210819195533.211756-1-hannes@cmpxchg.org>
References: <20210819195533.211756-1-hannes@cmpxchg.org>
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Clean up option ordering; make prompts and help text more concise and
actionable for non-developers; turn depends into selects where
possible, so that users can simply select the functionality they want
without having to chase down obscure code dependencies.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 drivers/block/zram/Kconfig |  3 ++-
 mm/Kconfig                 | 53 ++++++++++++++++++--------------------
 2 files changed, 27 insertions(+), 29 deletions(-)

diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig
index 668c6bf2554d..e4163d4b936b 100644
--- a/drivers/block/zram/Kconfig
+++ b/drivers/block/zram/Kconfig
@@ -1,8 +1,9 @@
 # SPDX-License-Identifier: GPL-2.0
 config ZRAM
 	tristate "Compressed RAM block device support"
-	depends on BLOCK && SYSFS && ZSMALLOC && CRYPTO
+	depends on BLOCK && SYSFS
 	depends on CRYPTO_LZO || CRYPTO_ZSTD || CRYPTO_LZ4 || CRYPTO_LZ4HC || CRYPTO_842
+	select ZSMALLOC
 	help
 	  Creates virtual block devices called /dev/zramX (X = 0, 1, ...).
 	  Pages written to these disks are compressed and stored in memory
diff --git a/mm/Kconfig b/mm/Kconfig
index dbceaa2a04a4..62c6e6092a0a 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -21,9 +21,13 @@ menuconfig SWAP
 
 if SWAP
 
+config ZPOOL
+	bool
+
 config ZSWAP
 	bool "Compressed cache for swap pages (EXPERIMENTAL)"
-	depends on FRONTSWAP && CRYPTO=y
+	select FRONTSWAP
+	select CRYPTO
 	select ZPOOL
 	help
 	  A lightweight compressed cache for swap pages.  It takes
@@ -39,8 +43,18 @@ config ZSWAP
 	  they have not be fully explored on the large set of potential
 	  configurations and workloads that exist.
 
+config ZSWAP_DEFAULT_ON
+	bool "Enable the compressed cache for swap pages by default"
+	depends on ZSWAP
+	help
+	  If selected, the compressed cache for swap pages will be enabled
+	  at boot, otherwise it will be disabled.
+
+	  The selection made here can be overridden by using the kernel
+	  command line 'zswap.enabled=' option.
+
 choice
-	prompt "Compressed cache for swap pages default compressor"
+	prompt "Default compressor"
 	depends on ZSWAP
 	default ZSWAP_COMPRESSOR_DEFAULT_LZO
 	help
@@ -106,7 +120,7 @@ config ZSWAP_COMPRESSOR_DEFAULT
        default ""
 
 choice
-	prompt "Compressed cache for swap pages default allocator"
+	prompt "Default allocator"
 	depends on ZSWAP
 	default ZSWAP_ZPOOL_DEFAULT_ZBUD
 	help
@@ -146,24 +160,9 @@ config ZSWAP_ZPOOL_DEFAULT
        default "zsmalloc" if ZSWAP_ZPOOL_DEFAULT_ZSMALLOC
        default ""
 
-config ZSWAP_DEFAULT_ON
-	bool "Enable the compressed cache for swap pages by default"
-	depends on ZSWAP
-	help
-	  If selected, the compressed cache for swap pages will be enabled
-	  at boot, otherwise it will be disabled.
-
-	  The selection made here can be overridden by using the kernel
-	  command line 'zswap.enabled=' option.
-
-config ZPOOL
-	tristate "Common API for compressed memory storage"
-	help
-	  Compressed memory storage API.  This allows using either zbud or
-	  zsmalloc.
-
 config ZBUD
-	tristate "Low (Up to 2x) density storage for compressed pages"
+	tristate "2:1 compression allocator (zbud)"
+	depends on ZSWAP
 	help
 	  A special purpose allocator for storing compressed pages.
 	  It is designed to store up to two compressed pages per physical
@@ -172,8 +171,8 @@ config ZBUD
 	  density approach when reclaim will be used.
 
 config Z3FOLD
-	tristate "Up to 3x density storage for compressed pages"
-	depends on ZPOOL
+	tristate "3:1 compression allocator (z3fold)"
+	depends on ZSWAP
 	help
 	  A special purpose allocator for storing compressed pages.
 	  It is designed to store up to three compressed pages per physical
@@ -181,15 +180,13 @@ config Z3FOLD
 	  still there.
 
 config ZSMALLOC
-	tristate "Memory allocator for compressed pages"
+	tristate
+	prompt "N:1 compression allocator (zsmalloc)" if ZSWAP
 	depends on MMU
 	help
 	  zsmalloc is a slab-based memory allocator designed to store
-	  compressed RAM pages.  zsmalloc uses virtual memory mapping
-	  in order to reduce fragmentation.  However, this results in a
-	  non-standard allocator interface where a handle, not a pointer, is
-	  returned by an alloc().  This handle must be mapped in order to
-	  access the allocated space.
+	  pages of various compression levels efficiently. It achieves
+	  the highest storage density with the least amount of fragmentation.
 
 config ZSMALLOC_STAT
 	bool "Export zsmalloc statistics"
-- 
2.32.0