[PATCH 4/4] zsmalloc: Use all available 24 bits of page_type

["Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>]

Now that we have an extra 8 bits, we don't need to limit ourselves to
supporting a 64KiB page size.  I'm sure both Hexagon users are grateful,
but it does reduce complexity a little.  We can also remove
reset_first_obj_offset() as calling __ClearPageZsmalloc() will now reset
all 32 bits of page_type.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
 drivers/block/zram/Kconfig |  1 -
 mm/Kconfig                 | 10 ++--------
 mm/zsmalloc.c              | 15 ++++-----------
 3 files changed, 6 insertions(+), 20 deletions(-)

diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig
index 40e035468de2..6aea609b795c 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 && MMU
-	depends on HAVE_ZSMALLOC
 	select ZSMALLOC
 	help
 	  Creates virtual block devices called /dev/zramX (X = 0, 1, ...).
diff --git a/mm/Kconfig b/mm/Kconfig
index 3936fe4d26d9..5946dcdcaeda 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -128,7 +128,7 @@ config ZSWAP_COMPRESSOR_DEFAULT
 choice
 	prompt "Default allocator"
 	depends on ZSWAP
-	default ZSWAP_ZPOOL_DEFAULT_ZSMALLOC if HAVE_ZSMALLOC
+	default ZSWAP_ZPOOL_DEFAULT_ZSMALLOC if MMU
 	default ZSWAP_ZPOOL_DEFAULT_ZBUD
 	help
 	  Selects the default allocator for the compressed cache for
@@ -154,7 +154,6 @@ config ZSWAP_ZPOOL_DEFAULT_Z3FOLD
 
 config ZSWAP_ZPOOL_DEFAULT_ZSMALLOC
 	bool "zsmalloc"
-	depends on HAVE_ZSMALLOC
 	select ZSMALLOC
 	help
 	  Use the zsmalloc allocator as the default allocator.
@@ -187,15 +186,10 @@ config Z3FOLD
 	  page. It is a ZBUD derivative so the simplicity and determinism are
 	  still there.
 
-config HAVE_ZSMALLOC
-	def_bool y
-	depends on MMU
-	depends on PAGE_SIZE_LESS_THAN_256KB # we want <= 64 KiB
-
 config ZSMALLOC
 	tristate
 	prompt "N:1 compression allocator (zsmalloc)" if ZSWAP
-	depends on HAVE_ZSMALLOC
+	depends on MMU
 	help
 	  zsmalloc is a slab-based memory allocator designed to store
 	  pages of various compression levels efficiently. It achieves
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 2d3163e4da96..73a3ec5b21ad 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -20,7 +20,7 @@
  *	page->index: links together all component pages of a zspage
  *		For the huge page, this is always 0, so we use this field
  *		to store handle.
- *	page->page_type: PG_zsmalloc, lower 16 bit locate the first object
+ *	page->page_type: PGTY_zsmalloc, lower 24 bits locate the first object
  *		offset in a subpage of a zspage
  *
  * Usage of struct page flags:
@@ -452,13 +452,7 @@ static inline struct page *get_first_page(struct zspage *zspage)
 	return first_page;
 }
 
-#define FIRST_OBJ_PAGE_TYPE_MASK	0xffff
-
-static inline void reset_first_obj_offset(struct page *page)
-{
-	VM_WARN_ON_ONCE(!PageZsmalloc(page));
-	page->page_type |= FIRST_OBJ_PAGE_TYPE_MASK;
-}
+#define FIRST_OBJ_PAGE_TYPE_MASK	0xffffff
 
 static inline unsigned int get_first_obj_offset(struct page *page)
 {
@@ -468,8 +462,8 @@ static inline unsigned int get_first_obj_offset(struct page *page)
 
 static inline void set_first_obj_offset(struct page *page, unsigned int offset)
 {
-	/* With 16 bit available, we can support offsets into 64 KiB pages. */
-	BUILD_BUG_ON(PAGE_SIZE > SZ_64K);
+	/* With 24 bits available, we can support offsets into 16 MiB pages. */
+	BUILD_BUG_ON(PAGE_SIZE > SZ_16M);
 	VM_WARN_ON_ONCE(!PageZsmalloc(page));
 	VM_WARN_ON_ONCE(offset & ~FIRST_OBJ_PAGE_TYPE_MASK);
 	page->page_type &= ~FIRST_OBJ_PAGE_TYPE_MASK;
@@ -808,7 +802,6 @@ static void reset_page(struct page *page)
 	ClearPagePrivate(page);
 	set_page_private(page, 0);
 	page->index = 0;
-	reset_first_obj_offset(page);
 	__ClearPageZsmalloc(page);
 }
 
-- 
2.43.0