mm: z3fold: remove z3fold

Patch series "mm: zswap: remove z3fold and zbud", v2.

After 2 cycles of deprecating z3fold, remove it as well as zbud (rationale
in specific patches).


This patch (of 2):

Z3fold has been marked as deprecated for 2 cycles and no one complained,
as expected.  As there are no known users, remove the code now.

Link: https://lkml.kernel.org/r/20250129180633.3501650-1-yosry.ahmed@linux.dev
Link: https://lkml.kernel.org/r/20250129180633.3501650-2-yosry.ahmed@linux.dev
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: WANG Xuerui <kernel@xen0n.name>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

CREDITS

@@ -4311,6 +4311,7 @@ S: England
 N: Vitaly Wool
 E: vitaly.wool@konsulko.com
 D: Maintenance and development of zswap
+D: Maintenance and development of z3fold
 
 N: Chris Wright
 E: chrisw@sous-sol.org

Documentation/mm/index.rst

@@ -62,5 +62,4 @@ documentation, or deleted if it has served its purpose.
    unevictable-lru
    vmalloced-kernel-stacks
    vmemmap_dedup
-   z3fold
    zsmalloc

Documentation/mm/z3fold.rst

@@ -1,28 +0,0 @@
-======
-z3fold
-======
-
-z3fold is a special purpose allocator for storing compressed pages.
-It is designed to store up to three compressed pages per physical page.
-It is a zbud derivative which allows for higher compression
-ratio keeping the simplicity and determinism of its predecessor.
-
-The main differences between z3fold and zbud are:
-
-* unlike zbud, z3fold allows for up to PAGE_SIZE allocations
-* z3fold can hold up to 3 compressed pages in its page
-* z3fold doesn't export any API itself and is thus intended to be used
-  via the zpool API.
-
-To keep the determinism and simplicity, z3fold, just like zbud, always
-stores an integral number of compressed pages per page, but it can store
-up to 3 pages unlike zbud which can store at most 2. Therefore the
-compression ratio goes to around 2.7x while zbud's one is around 1.7x.
-
-Unlike zbud (but like zsmalloc for that matter) z3fold_alloc() does not
-return a dereferenceable pointer. Instead, it returns an unsigned long
-handle which encodes actual location of the allocated object.
-
-Keeping effective compression ratio close to zsmalloc's, z3fold doesn't
-depend on MMU enabled and provides more predictable reclaim behavior
-which makes it a better fit for small and response-critical systems.

Documentation/translations/zh_CN/mm/index.rst

@@ -58,7 +58,6 @@ Linux内存管理文档
    remap_file_pages
    split_page_table_lock
    vmalloced-kernel-stacks
-   z3fold
    zsmalloc
 
 TODOLIST:

Documentation/translations/zh_CN/mm/z3fold.rst

@@ -1,31 +0,0 @@
-:Original: Documentation/mm/z3fold.rst
-
-:翻译:
-
- 司延腾 Yanteng Si <siyanteng@loongson.cn>
-
-:校译:
-
-
-======
-z3fold
-======
-
-z3fold是一个专门用于存储压缩页的分配器。它被设计为每个物理页最多可以存储三个压缩页。
-它是zbud的衍生物，允许更高的压缩率，保持其前辈的简单性和确定性。
-
-z3fold和zbud的主要区别是:
-
-* 与zbud不同的是，z3fold允许最大的PAGE_SIZE分配。
-* z3fold在其页面中最多可以容纳3个压缩页面
-* z3fold本身没有输出任何API，因此打算通过zpool的API来使用
-
-为了保持确定性和简单性，z3fold，就像zbud一样，总是在每页存储一个整数的压缩页，但是
-它最多可以存储3页，不像zbud最多可以存储2页。因此压缩率达到2.7倍左右，而zbud的压缩
-率是1.7倍左右。
-
-不像zbud（但也像zsmalloc），z3fold_alloc()那样不返回一个可重复引用的指针。相反，它
-返回一个无符号长句柄，它编码了被分配对象的实际位置。
-
-保持有效的压缩率接近于zsmalloc，z3fold不依赖于MMU的启用，并提供更可预测的回收行
-为，这使得它更适合于小型和反应迅速的系统。

MAINTAINERS

@@ -26181,13 +26181,6 @@ S:	Maintained
 F:	Documentation/input/devices/yealink.rst
 F:	drivers/input/misc/yealink.*
 
-Z3FOLD COMPRESSED PAGE ALLOCATOR
-M:	Vitaly Wool <vitaly.wool@konsulko.com>
-R:	Miaohe Lin <linmiaohe@huawei.com>
-L:	linux-mm@kvack.org
-S:	Maintained
-F:	mm/z3fold.c
-
 Z8530 DRIVER FOR AX.25
 M:	Joerg Reuter <jreuter@yaina.de>
 L:	linux-hams@vger.kernel.org

mm/Kconfig

@@ -146,15 +146,6 @@ config ZSWAP_ZPOOL_DEFAULT_ZBUD
 	help
 	  Use the zbud allocator as the default allocator.
 
-config ZSWAP_ZPOOL_DEFAULT_Z3FOLD_DEPRECATED
-	bool "z3foldi (DEPRECATED)"
-	select Z3FOLD_DEPRECATED
-	help
-	  Use the z3fold allocator as the default allocator.
-
-	  Deprecated and scheduled for removal in a few cycles,
-	  see CONFIG_Z3FOLD_DEPRECATED.
-
 config ZSWAP_ZPOOL_DEFAULT_ZSMALLOC
 	bool "zsmalloc"
 	select ZSMALLOC
@@ -166,7 +157,6 @@ config ZSWAP_ZPOOL_DEFAULT
        string
        depends on ZSWAP
        default "zbud" if ZSWAP_ZPOOL_DEFAULT_ZBUD
-       default "z3fold" if ZSWAP_ZPOOL_DEFAULT_Z3FOLD_DEPRECATED
        default "zsmalloc" if ZSWAP_ZPOOL_DEFAULT_ZSMALLOC
        default ""
 
@@ -180,25 +170,6 @@ config ZBUD
 	  deterministic reclaim properties that make it preferable to a higher
 	  density approach when reclaim will be used.
 
-config Z3FOLD_DEPRECATED
-	tristate "3:1 compression allocator (z3fold) (DEPRECATED)"
-	depends on ZSWAP
-	help
-	  Deprecated and scheduled for removal in a few cycles. If you have
-	  a good reason for using Z3FOLD over ZSMALLOC, please contact
-	  linux-mm@kvack.org and the zswap maintainers.
-
-	  A special purpose allocator for storing compressed pages.
-	  It is designed to store up to three compressed pages per physical
-	  page. It is a ZBUD derivative so the simplicity and determinism are
-	  still there.
-
-config Z3FOLD
-	tristate
-	default y if Z3FOLD_DEPRECATED=y
-	default m if Z3FOLD_DEPRECATED=m
-	depends on Z3FOLD_DEPRECATED
-
 config ZSMALLOC
 	tristate
 	prompt "N:1 compression allocator (zsmalloc)" if (ZSWAP || ZRAM)

mm/Makefile

@@ -115,7 +115,6 @@ obj-$(CONFIG_MEMORY_ISOLATION) += page_isolation.o
 obj-$(CONFIG_ZPOOL)	+= zpool.o
 obj-$(CONFIG_ZBUD)	+= zbud.o
 obj-$(CONFIG_ZSMALLOC)	+= zsmalloc.o
-obj-$(CONFIG_Z3FOLD)	+= z3fold.o
 obj-$(CONFIG_GENERIC_EARLY_IOREMAP) += early_ioremap.o
 obj-$(CONFIG_CMA)	+= cma.o
 obj-$(CONFIG_NUMA) += numa.o