[PATCH 00/20] mm/zsmalloc: add zpdesc memory descriptor for zswap.zpool

[PATCH 00/20] mm/zsmalloc: add zpdesc memory descriptor for zswap.zpool

[alexs]

From: Alex Shi <alexs@kernel.org>

According to Metthew's plan, the page descriptor will be replace by a 8
bytes mem_desc on destination purpose.
https://lore.kernel.org/lkml/YvV1KTyzZ+Jrtj9x@casper.infradead.org/

Here is a implement on zsmalloc to replace page descriptor by 'zpdesc',
which is still overlay on struct page now. but it's a step move forward
above destination.

To name the struct zpdesc instead of zsdesc, since there are still 3
zpools under zswap: zbud, z3fold, zsmalloc for now(z3fold maybe removed
soon), and we could easyly extend it to other zswap.zpool in needs.

For all zswap.zpools, they are all using single page since often used
under memory pressure. So the conversion via folio series helper is
better than page's for compound_head check saving.

For now, all zpools are using some page struct members, like page.flags
for PG_private/PG_locked. and list_head lru, page.mapping for page migration.

This patachset could save 123Kbyetes zsmalloc.o size.

Thanks
Alex

Alex Shi (8):
  mm/zsmalloc: add zpdesc memory descriptor for zswap.zpool
  mm/zsmalloc: use zpdesc in trylock_zspage/lock_zspage
  mm/zsmalloc: convert create_page_chain() and its users to use zpdesc
  mm/zsmalloc: rename reset_page to reset_zpdesc and use zpdesc in it
  mm/zsmalloc: convert SetZsPageMovable and remove unused funcs
  mm/zsmalloc: introduce __zpdesc_clear_movable
  mm/zsmalloc: introduce __zpdesc_clear_zsmalloc
  mm/zsmalloc: introduce __zpdesc_set_zsmalloc()

Hyeonggon Yoo (12):
  mm/zsmalloc: convert __zs_map_object/__zs_unmap_object to use zpdesc
  mm/zsmalloc: add and use pfn/zpdesc seeking funcs
  mm/zsmalloc: convert obj_malloc() to use zpdesc
  mm/zsmalloc: convert obj_allocated() and related helpers to use zpdesc
  mm/zsmalloc: convert init_zspage() to use zpdesc
  mm/zsmalloc: convert obj_to_page() and zs_free() to use zpdesc
  mm/zsmalloc: add zpdesc_is_isolated/zpdesc_zone helper for
    zs_page_migrate
  mm/zsmalloc: convert __free_zspage() to use zdsesc
  mm/zsmalloc: convert location_to_obj() to take zpdesc
  mm/zsmalloc: convert migrate_zspage() to use zpdesc
  mm/zsmalloc: convert get_zspage() to take zpdesc
  mm/zsmalloc: convert get/set_first_obj_offset() to take zpdesc

 mm/zpdesc.h   | 134 +++++++++++++++
 mm/zsmalloc.c | 454 +++++++++++++++++++++++++++-----------------------
 2 files changed, 384 insertions(+), 204 deletions(-)
 create mode 100644 mm/zpdesc.h

-- 
2.43.0

[PATCH 01/20] mm/zsmalloc: add zpdesc memory descriptor for zswap.zpool

[alexs]

From: Alex Shi <alexs@kernel.org>

The 1st patch introduces new memory decriptor zpdesc and rename
zspage.first_page to zspage.first_zpdesc, no functional change.

Originally-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Alex Shi <alexs@kernel.org>
---
 mm/zpdesc.h   | 56 +++++++++++++++++++++++++++++++++++++++++++++++++++
 mm/zsmalloc.c | 19 ++++++++---------
 2 files changed, 66 insertions(+), 9 deletions(-)
 create mode 100644 mm/zpdesc.h

diff --git a/mm/zpdesc.h b/mm/zpdesc.h
new file mode 100644
index 000000000000..a1ab5ebaa936
--- /dev/null
+++ b/mm/zpdesc.h
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* zpdesc.h: zswap.zpool memory descriptor
+ *
+ * Written by Alex Shi <alexs@kernel.org>
+ *	      Hyeonggon Yoo <42.hyeyoo@gmail.com>
+ */
+#ifndef __MM_ZPDESC_H__
+#define __MM_ZPDESC_H__
+
+/*
+ * struct zpdesc -	Memory descriptor for zpool memory, now is for zsmalloc
+ * @flags:		Page flags, PG_private: identifies the first component page
+ * @lru:		Indirected used by page migration
+ * @next:		Next zpdesc in a zspage in zsmalloc zpool
+ * @handle:		For huge zspage in zsmalloc zpool
+ * @zspage:		Pointer to zspage in zsmalloc
+ *
+ * This struct overlays struct page for now. Do not modify without a good
+ * understanding of the issues.
+ */
+struct zpdesc {
+	unsigned long flags;
+	struct list_head lru;
+	unsigned long _zp_pad_1;
+	union {
+		/* Next zpdescs in a zspage in zsmalloc zpool */
+		struct zpdesc *next;
+		/* For huge zspage in zsmalloc zpool */
+		unsigned long handle;
+	};
+	struct zspage *zspage;
+};
+#define ZPDESC_MATCH(pg, zp) \
+	static_assert(offsetof(struct page, pg) == offsetof(struct zpdesc, zp))
+
+ZPDESC_MATCH(flags, flags);
+ZPDESC_MATCH(lru, lru);
+ZPDESC_MATCH(index, next);
+ZPDESC_MATCH(index, handle);
+ZPDESC_MATCH(private, zspage);
+#undef ZPDESC_MATCH
+static_assert(sizeof(struct zpdesc) <= sizeof(struct page));
+
+#define zpdesc_page(zp)			(_Generic((zp),			\
+	const struct zpdesc *:		(const struct page *)(zp),	\
+	struct zpdesc *:		(struct page *)(zp)))
+
+#define zpdesc_folio(zp)		(_Generic((zp),			\
+	const struct zpdesc *:		(const struct folio *)(zp),	\
+	struct zpdesc *:		(struct folio *)(zp)))
+
+#define page_zpdesc(p)			(_Generic((p),			\
+	const struct page *:		(const struct zpdesc *)(p),	\
+	struct page *:			(struct zpdesc *)(p)))
+
+#endif
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index fec1a39e5bbe..67bb80b7413a 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -13,17 +13,17 @@
 
 /*
  * Following is how we use various fields and flags of underlying
- * struct page(s) to form a zspage.
+ * struct zpdesc(page) to form a zspage.
  *
- * Usage of struct page fields:
- *	page->private: points to zspage
- *	page->index: links together all component pages of a zspage
+ * Usage of struct zpdesc fields:
+ *	zpdesc->zspage: points to zspage
+ *	zpdesc->next: 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
  *		offset in a subpage of a zspage
  *
- * Usage of struct page flags:
+ * Usage of struct zpdesc(page) flags:
  *	PG_private: identifies the first component page
  *	PG_owner_priv_1: identifies the huge component page
  *
@@ -64,6 +64,7 @@
 #include <linux/pagemap.h>
 #include <linux/fs.h>
 #include <linux/local_lock.h>
+#include "zpdesc.h"
 
 #define ZSPAGE_MAGIC	0x58
 
@@ -253,7 +254,7 @@ struct zspage {
 	};
 	unsigned int inuse;
 	unsigned int freeobj;
-	struct page *first_page;
+	struct zpdesc *first_zpdesc;
 	struct list_head list; /* fullness list */
 	struct zs_pool *pool;
 	rwlock_t lock;
@@ -448,7 +449,7 @@ static inline void mod_zspage_inuse(struct zspage *zspage, int val)
 
 static inline struct page *get_first_page(struct zspage *zspage)
 {
-	struct page *first_page = zspage->first_page;
+	struct page *first_page = zpdesc_page(zspage->first_zpdesc);
 
 	VM_BUG_ON_PAGE(!is_first_page(first_page), first_page);
 	return first_page;
@@ -948,7 +949,7 @@ static void create_page_chain(struct size_class *class, struct zspage *zspage,
 		set_page_private(page, (unsigned long)zspage);
 		page->index = 0;
 		if (i == 0) {
-			zspage->first_page = page;
+			zspage->first_zpdesc = page_zpdesc(page);
 			SetPagePrivate(page);
 			if (unlikely(class->objs_per_zspage == 1 &&
 					class->pages_per_zspage == 1))
@@ -1325,7 +1326,7 @@ static unsigned long obj_malloc(struct zs_pool *pool,
 		link->handle = handle;
 	else
 		/* record handle to page->index */
-		zspage->first_page->index = handle;
+		zspage->first_zpdesc->handle = handle;
 
 	kunmap_atomic(vaddr);
 	mod_zspage_inuse(zspage, 1);
-- 
2.43.0

[PATCH 02/20] mm/zsmalloc: use zpdesc in trylock_zspage/lock_zspage

[alexs]

From: Alex Shi <alexs@kernel.org>

To use zpdesc in trylock_zspage/lock_zspage funcs, we add couple of helpers:
zpdesc_lock/zpdesc_unlock/zpdesc_trylock/zpdesc_wait_locked and
zpdesc_get/zpdesc_put for this purpose.

Here we use the folio series func in guts for 2 reasons, one zswap.zpool
only get single page, and use folio could save some compound_head checking;
two, folio_put could bypass devmap checking that we don't need.

Originally-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Alex Shi <alexs@kernel.org>
---
 mm/zpdesc.h   | 30 ++++++++++++++++++++++++
 mm/zsmalloc.c | 64 ++++++++++++++++++++++++++++++++++-----------------
 2 files changed, 73 insertions(+), 21 deletions(-)

diff --git a/mm/zpdesc.h b/mm/zpdesc.h
index a1ab5ebaa936..fd95277843d5 100644
--- a/mm/zpdesc.h
+++ b/mm/zpdesc.h
@@ -53,4 +53,34 @@ static_assert(sizeof(struct zpdesc) <= sizeof(struct page));
 	const struct page *:		(const struct zpdesc *)(p),	\
 	struct page *:			(struct zpdesc *)(p)))
 
+static inline void zpdesc_lock(struct zpdesc *zpdesc)
+{
+	folio_lock(zpdesc_folio(zpdesc));
+}
+
+static inline bool zpdesc_trylock(struct zpdesc *zpdesc)
+{
+	return folio_trylock(zpdesc_folio(zpdesc));
+}
+
+static inline void zpdesc_unlock(struct zpdesc *zpdesc)
+{
+	folio_unlock(zpdesc_folio(zpdesc));
+}
+
+static inline void zpdesc_wait_locked(struct zpdesc *zpdesc)
+{
+	folio_wait_locked(zpdesc_folio(zpdesc));
+}
+
+static inline void zpdesc_get(struct zpdesc *zpdesc)
+{
+	folio_get(zpdesc_folio(zpdesc));
+}
+
+static inline void zpdesc_put(struct zpdesc *zpdesc)
+{
+	folio_put(zpdesc_folio(zpdesc));
+}
+
 #endif
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 67bb80b7413a..9835121109d1 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -435,13 +435,17 @@ static __maybe_unused int is_first_page(struct page *page)
 	return PagePrivate(page);
 }
 
+static int is_first_zpdesc(struct zpdesc *zpdesc)
+{
+	return PagePrivate(zpdesc_page(zpdesc));
+}
+
 /* Protected by class->lock */
 static inline int get_zspage_inuse(struct zspage *zspage)
 {
 	return zspage->inuse;
 }
 
-
 static inline void mod_zspage_inuse(struct zspage *zspage, int val)
 {
 	zspage->inuse += val;
@@ -455,6 +459,14 @@ static inline struct page *get_first_page(struct zspage *zspage)
 	return first_page;
 }
 
+static struct zpdesc *get_first_zpdesc(struct zspage *zspage)
+{
+	struct zpdesc *first_zpdesc = zspage->first_zpdesc;
+
+	VM_BUG_ON_PAGE(!is_first_zpdesc(first_zpdesc), zpdesc_page(first_zpdesc));
+	return first_zpdesc;
+}
+
 #define FIRST_OBJ_PAGE_TYPE_MASK	0xffff
 
 static inline void reset_first_obj_offset(struct page *page)
@@ -747,6 +759,16 @@ static struct page *get_next_page(struct page *page)
 	return (struct page *)page->index;
 }
 
+static struct zpdesc *get_next_zpdesc(struct zpdesc *zpdesc)
+{
+	struct zspage *zspage = get_zspage(zpdesc_page(zpdesc));
+
+	if (unlikely(ZsHugePage(zspage)))
+		return NULL;
+
+	return zpdesc->next;
+}
+
 /**
  * obj_to_location - get (<page>, <obj_idx>) from encoded object value
  * @obj: the encoded object value
@@ -817,11 +839,11 @@ static void reset_page(struct page *page)
 
 static int trylock_zspage(struct zspage *zspage)
 {
-	struct page *cursor, *fail;
+	struct zpdesc *cursor, *fail;
 
-	for (cursor = get_first_page(zspage); cursor != NULL; cursor =
-					get_next_page(cursor)) {
-		if (!trylock_page(cursor)) {
+	for (cursor = get_first_zpdesc(zspage); cursor != NULL; cursor =
+					get_next_zpdesc(cursor)) {
+		if (!zpdesc_trylock(cursor)) {
 			fail = cursor;
 			goto unlock;
 		}
@@ -829,9 +851,9 @@ static int trylock_zspage(struct zspage *zspage)
 
 	return 1;
 unlock:
-	for (cursor = get_first_page(zspage); cursor != fail; cursor =
-					get_next_page(cursor))
-		unlock_page(cursor);
+	for (cursor = get_first_zpdesc(zspage); cursor != fail; cursor =
+					get_next_zpdesc(cursor))
+		zpdesc_unlock(cursor);
 
 	return 0;
 }
@@ -1663,7 +1685,7 @@ static int putback_zspage(struct size_class *class, struct zspage *zspage)
  */
 static void lock_zspage(struct zspage *zspage)
 {
-	struct page *curr_page, *page;
+	struct zpdesc *curr_zpdesc, *zpdesc;
 
 	/*
 	 * Pages we haven't locked yet can be migrated off the list while we're
@@ -1675,24 +1697,24 @@ static void lock_zspage(struct zspage *zspage)
 	 */
 	while (1) {
 		migrate_read_lock(zspage);
-		page = get_first_page(zspage);
-		if (trylock_page(page))
+		zpdesc = get_first_zpdesc(zspage);
+		if (zpdesc_trylock(zpdesc))
 			break;
-		get_page(page);
+		zpdesc_get(zpdesc);
 		migrate_read_unlock(zspage);
-		wait_on_page_locked(page);
-		put_page(page);
+		zpdesc_wait_locked(zpdesc);
+		zpdesc_put(zpdesc);
 	}
 
-	curr_page = page;
-	while ((page = get_next_page(curr_page))) {
-		if (trylock_page(page)) {
-			curr_page = page;
+	curr_zpdesc = zpdesc;
+	while ((zpdesc = get_next_zpdesc(curr_zpdesc))) {
+		if (zpdesc_trylock(zpdesc)) {
+			curr_zpdesc = zpdesc;
 		} else {
-			get_page(page);
+			zpdesc_get(zpdesc);
 			migrate_read_unlock(zspage);
-			wait_on_page_locked(page);
-			put_page(page);
+			zpdesc_wait_locked(zpdesc);
+			zpdesc_put(zpdesc);
 			migrate_read_lock(zspage);
 		}
 	}
-- 
2.43.0

[PATCH 03/20] mm/zsmalloc: convert __zs_map_object/__zs_unmap_object to use zpdesc

[alexs]

From: Hyeonggon Yoo <42.hyeyoo@gmail.com>

These two functions take pointer to an array of struct page. Introduce
zpdesc_kmap_atomic() and make __zs_{map,unmap}_object() take pointer
to an array of zpdesc instead of page.

Add silly type casting when calling them. Casting will be removed late.

Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Alex Shi <alexs@kernel.org>
---
 mm/zsmalloc.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 9835121109d1..cedd3dfb9124 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -245,6 +245,11 @@ struct zs_pool {
 	atomic_t compaction_in_progress;
 };
 
+static inline void *zpdesc_kmap_atomic(struct zpdesc *zpdesc)
+{
+	return kmap_atomic(zpdesc_page(zpdesc));
+}
+
 struct zspage {
 	struct {
 		unsigned int huge:HUGE_BITS;
@@ -1063,7 +1068,7 @@ static inline void __zs_cpu_down(struct mapping_area *area)
 }
 
 static void *__zs_map_object(struct mapping_area *area,
-			struct page *pages[2], int off, int size)
+			struct zpdesc *zpdescs[2], int off, int size)
 {
 	int sizes[2];
 	void *addr;
@@ -1080,10 +1085,10 @@ static void *__zs_map_object(struct mapping_area *area,
 	sizes[1] = size - sizes[0];
 
 	/* copy object to per-cpu buffer */
-	addr = kmap_atomic(pages[0]);
+	addr = zpdesc_kmap_atomic(zpdescs[0]);
 	memcpy(buf, addr + off, sizes[0]);
 	kunmap_atomic(addr);
-	addr = kmap_atomic(pages[1]);
+	addr = zpdesc_kmap_atomic(zpdescs[1]);
 	memcpy(buf + sizes[0], addr, sizes[1]);
 	kunmap_atomic(addr);
 out:
@@ -1091,7 +1096,7 @@ static void *__zs_map_object(struct mapping_area *area,
 }
 
 static void __zs_unmap_object(struct mapping_area *area,
-			struct page *pages[2], int off, int size)
+			struct zpdesc *zpdescs[2], int off, int size)
 {
 	int sizes[2];
 	void *addr;
@@ -1110,10 +1115,10 @@ static void __zs_unmap_object(struct mapping_area *area,
 	sizes[1] = size - sizes[0];
 
 	/* copy per-cpu buffer to object */
-	addr = kmap_atomic(pages[0]);
+	addr = zpdesc_kmap_atomic(zpdescs[0]);
 	memcpy(addr + off, buf, sizes[0]);
 	kunmap_atomic(addr);
-	addr = kmap_atomic(pages[1]);
+	addr = zpdesc_kmap_atomic(zpdescs[1]);
 	memcpy(addr, buf + sizes[0], sizes[1]);
 	kunmap_atomic(addr);
 
@@ -1254,7 +1259,7 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
 	pages[1] = get_next_page(page);
 	BUG_ON(!pages[1]);
 
-	ret = __zs_map_object(area, pages, off, class->size);
+	ret = __zs_map_object(area, (struct zpdesc **)pages, off, class->size);
 out:
 	if (likely(!ZsHugePage(zspage)))
 		ret += ZS_HANDLE_SIZE;
@@ -1289,7 +1294,7 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
 		pages[1] = get_next_page(page);
 		BUG_ON(!pages[1]);
 
-		__zs_unmap_object(area, pages, off, class->size);
+		__zs_unmap_object(area, (struct zpdesc **)pages, off, class->size);
 	}
 	local_unlock(&zs_map_area.lock);
 
-- 
2.43.0

[PATCH 04/20] mm/zsmalloc: add and use pfn/zpdesc seeking funcs

[alexs]

From: Hyeonggon Yoo <42.hyeyoo@gmail.com>

Add pfn_zpdesc conversion, convert obj_to_location() to take zpdesc
and also convert its users to use zpdesc.

Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Alex Shi <alexs@kernel.org>
---
 mm/zpdesc.h   |  9 +++++++
 mm/zsmalloc.c | 75 ++++++++++++++++++++++++++-------------------------
 2 files changed, 47 insertions(+), 37 deletions(-)

diff --git a/mm/zpdesc.h b/mm/zpdesc.h
index fd95277843d5..3c0ebdc78ff8 100644
--- a/mm/zpdesc.h
+++ b/mm/zpdesc.h
@@ -83,4 +83,13 @@ static inline void zpdesc_put(struct zpdesc *zpdesc)
 	folio_put(zpdesc_folio(zpdesc));
 }
 
+static inline unsigned long zpdesc_pfn(struct zpdesc *zpdesc)
+{
+	return page_to_pfn(zpdesc_page(zpdesc));
+}
+
+static inline struct zpdesc *pfn_zpdesc(unsigned long pfn)
+{
+	return page_zpdesc(pfn_to_page(pfn));
+}
 #endif
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index cedd3dfb9124..efb1d58b3c36 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -775,15 +775,15 @@ static struct zpdesc *get_next_zpdesc(struct zpdesc *zpdesc)
 }
 
 /**
- * obj_to_location - get (<page>, <obj_idx>) from encoded object value
+ * obj_to_location - get (<zpdesc>, <obj_idx>) from encoded object value
  * @obj: the encoded object value
- * @page: page object resides in zspage
+ * @zpdesc: zpdesc object resides in zspage
  * @obj_idx: object index
  */
-static void obj_to_location(unsigned long obj, struct page **page,
+static void obj_to_location(unsigned long obj, struct zpdesc **zpdesc,
 				unsigned int *obj_idx)
 {
-	*page = pfn_to_page(obj >> OBJ_INDEX_BITS);
+	*zpdesc = pfn_zpdesc(obj >> OBJ_INDEX_BITS);
 	*obj_idx = (obj & OBJ_INDEX_MASK);
 }
 
@@ -1210,13 +1210,13 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
 			enum zs_mapmode mm)
 {
 	struct zspage *zspage;
-	struct page *page;
+	struct zpdesc *zpdesc;
 	unsigned long obj, off;
 	unsigned int obj_idx;
 
 	struct size_class *class;
 	struct mapping_area *area;
-	struct page *pages[2];
+	struct zpdesc *zpdescs[2];
 	void *ret;
 
 	/*
@@ -1229,8 +1229,8 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
 	/* It guarantees it can get zspage from handle safely */
 	read_lock(&pool->migrate_lock);
 	obj = handle_to_obj(handle);
-	obj_to_location(obj, &page, &obj_idx);
-	zspage = get_zspage(page);
+	obj_to_location(obj, &zpdesc, &obj_idx);
+	zspage = get_zspage(zpdesc_page(zpdesc));
 
 	/*
 	 * migration cannot move any zpages in this zspage. Here, class->lock
@@ -1249,17 +1249,17 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
 	area->vm_mm = mm;
 	if (off + class->size <= PAGE_SIZE) {
 		/* this object is contained entirely within a page */
-		area->vm_addr = kmap_atomic(page);
+		area->vm_addr = zpdesc_kmap_atomic(zpdesc);
 		ret = area->vm_addr + off;
 		goto out;
 	}
 
 	/* this object spans two pages */
-	pages[0] = page;
-	pages[1] = get_next_page(page);
-	BUG_ON(!pages[1]);
+	zpdescs[0] = zpdesc;
+	zpdescs[1] = get_next_zpdesc(zpdesc);
+	BUG_ON(!zpdescs[1]);
 
-	ret = __zs_map_object(area, (struct zpdesc **)pages, off, class->size);
+	ret = __zs_map_object(area, zpdescs, off, class->size);
 out:
 	if (likely(!ZsHugePage(zspage)))
 		ret += ZS_HANDLE_SIZE;
@@ -1271,7 +1271,7 @@ EXPORT_SYMBOL_GPL(zs_map_object);
 void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
 {
 	struct zspage *zspage;
-	struct page *page;
+	struct zpdesc *zpdesc;
 	unsigned long obj, off;
 	unsigned int obj_idx;
 
@@ -1279,8 +1279,8 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
 	struct mapping_area *area;
 
 	obj = handle_to_obj(handle);
-	obj_to_location(obj, &page, &obj_idx);
-	zspage = get_zspage(page);
+	obj_to_location(obj, &zpdesc, &obj_idx);
+	zspage = get_zspage(zpdesc_page(zpdesc));
 	class = zspage_class(pool, zspage);
 	off = offset_in_page(class->size * obj_idx);
 
@@ -1288,13 +1288,13 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
 	if (off + class->size <= PAGE_SIZE)
 		kunmap_atomic(area->vm_addr);
 	else {
-		struct page *pages[2];
+		struct zpdesc *zpdescs[2];
 
-		pages[0] = page;
-		pages[1] = get_next_page(page);
-		BUG_ON(!pages[1]);
+		zpdescs[0] = zpdesc;
+		zpdescs[1] = get_next_zpdesc(zpdesc);
+		BUG_ON(!zpdescs[1]);
 
-		__zs_unmap_object(area, (struct zpdesc **)pages, off, class->size);
+		__zs_unmap_object(area, zpdescs, off, class->size);
 	}
 	local_unlock(&zs_map_area.lock);
 
@@ -1438,23 +1438,24 @@ static void obj_free(int class_size, unsigned long obj)
 {
 	struct link_free *link;
 	struct zspage *zspage;
-	struct page *f_page;
+	struct zpdesc *f_zpdesc;
 	unsigned long f_offset;
 	unsigned int f_objidx;
 	void *vaddr;
 
-	obj_to_location(obj, &f_page, &f_objidx);
+
+	obj_to_location(obj, &f_zpdesc, &f_objidx);
 	f_offset = offset_in_page(class_size * f_objidx);
-	zspage = get_zspage(f_page);
+	zspage = get_zspage(zpdesc_page(f_zpdesc));
 
-	vaddr = kmap_atomic(f_page);
+	vaddr = zpdesc_kmap_atomic(f_zpdesc);
 	link = (struct link_free *)(vaddr + f_offset);
 
 	/* Insert this object in containing zspage's freelist */
 	if (likely(!ZsHugePage(zspage)))
 		link->next = get_freeobj(zspage) << OBJ_TAG_BITS;
 	else
-		f_page->index = 0;
+		f_zpdesc->next = NULL;
 	set_freeobj(zspage, f_objidx);
 
 	kunmap_atomic(vaddr);
@@ -1499,7 +1500,7 @@ EXPORT_SYMBOL_GPL(zs_free);
 static void zs_object_copy(struct size_class *class, unsigned long dst,
 				unsigned long src)
 {
-	struct page *s_page, *d_page;
+	struct zpdesc *s_zpdesc, *d_zpdesc;
 	unsigned int s_objidx, d_objidx;
 	unsigned long s_off, d_off;
 	void *s_addr, *d_addr;
@@ -1508,8 +1509,8 @@ static void zs_object_copy(struct size_class *class, unsigned long dst,
 
 	s_size = d_size = class->size;
 
-	obj_to_location(src, &s_page, &s_objidx);
-	obj_to_location(dst, &d_page, &d_objidx);
+	obj_to_location(src, &s_zpdesc, &s_objidx);
+	obj_to_location(dst, &d_zpdesc, &d_objidx);
 
 	s_off = offset_in_page(class->size * s_objidx);
 	d_off = offset_in_page(class->size * d_objidx);
@@ -1520,8 +1521,8 @@ static void zs_object_copy(struct size_class *class, unsigned long dst,
 	if (d_off + class->size > PAGE_SIZE)
 		d_size = PAGE_SIZE - d_off;
 
-	s_addr = kmap_atomic(s_page);
-	d_addr = kmap_atomic(d_page);
+	s_addr = zpdesc_kmap_atomic(s_zpdesc);
+	d_addr = zpdesc_kmap_atomic(d_zpdesc);
 
 	while (1) {
 		size = min(s_size, d_size);
@@ -1546,17 +1547,17 @@ static void zs_object_copy(struct size_class *class, unsigned long dst,
 		if (s_off >= PAGE_SIZE) {
 			kunmap_atomic(d_addr);
 			kunmap_atomic(s_addr);
-			s_page = get_next_page(s_page);
-			s_addr = kmap_atomic(s_page);
-			d_addr = kmap_atomic(d_page);
+			s_zpdesc = get_next_zpdesc(s_zpdesc);
+			s_addr = zpdesc_kmap_atomic(s_zpdesc);
+			d_addr = zpdesc_kmap_atomic(d_zpdesc);
 			s_size = class->size - written;
 			s_off = 0;
 		}
 
 		if (d_off >= PAGE_SIZE) {
 			kunmap_atomic(d_addr);
-			d_page = get_next_page(d_page);
-			d_addr = kmap_atomic(d_page);
+			d_zpdesc = get_next_zpdesc(d_zpdesc);
+			d_addr = zpdesc_kmap_atomic(d_zpdesc);
 			d_size = class->size - written;
 			d_off = 0;
 		}
@@ -1796,7 +1797,7 @@ static int zs_page_migrate(struct page *newpage, struct page *page,
 	struct zs_pool *pool;
 	struct size_class *class;
 	struct zspage *zspage;
-	struct page *dummy;
+	struct zpdesc *dummy;
 	void *s_addr, *d_addr, *addr;
 	unsigned int offset;
 	unsigned long handle;
-- 
2.43.0

[PATCH 05/20] mm/zsmalloc: convert obj_malloc() to use zpdesc

[alexs]

From: Hyeonggon Yoo <42.hyeyoo@gmail.com>

Use get_first_zpdesc/get_next_zpdesc to replace
get_first_page/get_next_page. no functional change.

Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Alex Shi <alexs@kernel.org>
---
 mm/zsmalloc.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index efb1d58b3c36..137b36515acf 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -1324,12 +1324,12 @@ EXPORT_SYMBOL_GPL(zs_huge_class_size);
 static unsigned long obj_malloc(struct zs_pool *pool,
 				struct zspage *zspage, unsigned long handle)
 {
-	int i, nr_page, offset;
+	int i, nr_zpdesc, offset;
 	unsigned long obj;
 	struct link_free *link;
 	struct size_class *class;
 
-	struct page *m_page;
+	struct zpdesc *m_zpdesc;
 	unsigned long m_offset;
 	void *vaddr;
 
@@ -1338,14 +1338,14 @@ static unsigned long obj_malloc(struct zs_pool *pool,
 	obj = get_freeobj(zspage);
 
 	offset = obj * class->size;
-	nr_page = offset >> PAGE_SHIFT;
+	nr_zpdesc = offset >> PAGE_SHIFT;
 	m_offset = offset_in_page(offset);
-	m_page = get_first_page(zspage);
+	m_zpdesc = get_first_zpdesc(zspage);
 
-	for (i = 0; i < nr_page; i++)
-		m_page = get_next_page(m_page);
+	for (i = 0; i < nr_zpdesc; i++)
+		m_zpdesc = get_next_zpdesc(m_zpdesc);
 
-	vaddr = kmap_atomic(m_page);
+	vaddr = zpdesc_kmap_atomic(m_zpdesc);
 	link = (struct link_free *)vaddr + m_offset / sizeof(*link);
 	set_freeobj(zspage, link->next >> OBJ_TAG_BITS);
 	if (likely(!ZsHugePage(zspage)))
@@ -1358,7 +1358,7 @@ static unsigned long obj_malloc(struct zs_pool *pool,
 	kunmap_atomic(vaddr);
 	mod_zspage_inuse(zspage, 1);
 
-	obj = location_to_obj(m_page, obj);
+	obj = location_to_obj(zpdesc_page(m_zpdesc), obj);
 
 	return obj;
 }
-- 
2.43.0

[PATCH 06/20] mm/zsmalloc: convert create_page_chain() and its users to use zpdesc

[alexs]

From: Alex Shi <alexs@kernel.org>

Introduce a few helper functions for conversion to convert create_page_chain()
to use zpdesc, then use zpdesc in replace_sub_page() too.

Originally-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Alex Shi <alexs@kernel.org>
---
 mm/zpdesc.h   |   6 +++
 mm/zsmalloc.c | 115 +++++++++++++++++++++++++++++++++-----------------
 2 files changed, 82 insertions(+), 39 deletions(-)

diff --git a/mm/zpdesc.h b/mm/zpdesc.h
index 3c0ebdc78ff8..f998d65c59d6 100644
--- a/mm/zpdesc.h
+++ b/mm/zpdesc.h
@@ -92,4 +92,10 @@ static inline struct zpdesc *pfn_zpdesc(unsigned long pfn)
 {
 	return page_zpdesc(pfn_to_page(pfn));
 }
+
+static inline void __zpdesc_set_movable(struct zpdesc *zpdesc,
+					const struct movable_operations *mops)
+{
+	__SetPageMovable(zpdesc_page(zpdesc), mops);
+}
 #endif
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 137b36515acf..ee890d513f6f 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -250,6 +250,41 @@ static inline void *zpdesc_kmap_atomic(struct zpdesc *zpdesc)
 	return kmap_atomic(zpdesc_page(zpdesc));
 }
 
+static inline void zpdesc_set_zspage(struct zpdesc *zpdesc,
+				     struct zspage *zspage)
+{
+	zpdesc->zspage = zspage;
+}
+
+static inline void zpdesc_set_first(struct zpdesc *zpdesc)
+{
+	SetPagePrivate(zpdesc_page(zpdesc));
+}
+
+static inline void zpdesc_inc_zone_page_state(struct zpdesc *zpdesc)
+{
+	inc_zone_page_state(zpdesc_page(zpdesc), NR_ZSPAGES);
+}
+
+static inline void zpdesc_dec_zone_page_state(struct zpdesc *zpdesc)
+{
+	dec_zone_page_state(zpdesc_page(zpdesc), NR_ZSPAGES);
+}
+
+static inline struct zpdesc *alloc_zpdesc(gfp_t gfp)
+{
+	struct page *page = alloc_page(gfp);
+
+	return page_zpdesc(page);
+}
+
+static inline void free_zpdesc(struct zpdesc *zpdesc)
+{
+	struct page *page = zpdesc_page(zpdesc);
+
+	__free_page(page);
+}
+
 struct zspage {
 	struct {
 		unsigned int huge:HUGE_BITS;
@@ -956,35 +991,35 @@ static void init_zspage(struct size_class *class, struct zspage *zspage)
 }
 
 static void create_page_chain(struct size_class *class, struct zspage *zspage,
-				struct page *pages[])
+				struct zpdesc *zpdescs[])
 {
 	int i;
-	struct page *page;
-	struct page *prev_page = NULL;
-	int nr_pages = class->pages_per_zspage;
+	struct zpdesc *zpdesc;
+	struct zpdesc *prev_zpdesc = NULL;
+	int nr_zpdescs = class->pages_per_zspage;
 
 	/*
 	 * Allocate individual pages and link them together as:
-	 * 1. all pages are linked together using page->index
-	 * 2. each sub-page point to zspage using page->private
+	 * 1. all pages are linked together using zpdesc->next
+	 * 2. each sub-page point to zspage using zpdesc->zspage
 	 *
-	 * we set PG_private to identify the first page (i.e. no other sub-page
+	 * we set PG_private to identify the first zpdesc (i.e. no other zpdesc
 	 * has this flag set).
 	 */
-	for (i = 0; i < nr_pages; i++) {
-		page = pages[i];
-		set_page_private(page, (unsigned long)zspage);
-		page->index = 0;
+	for (i = 0; i < nr_zpdescs; i++) {
+		zpdesc = zpdescs[i];
+		zpdesc_set_zspage(zpdesc, zspage);
+		zpdesc->next = NULL;
 		if (i == 0) {
-			zspage->first_zpdesc = page_zpdesc(page);
-			SetPagePrivate(page);
+			zspage->first_zpdesc = zpdesc;
+			zpdesc_set_first(zpdesc);
 			if (unlikely(class->objs_per_zspage == 1 &&
 					class->pages_per_zspage == 1))
 				SetZsHugePage(zspage);
 		} else {
-			prev_page->index = (unsigned long)page;
+			prev_zpdesc->next = zpdesc;
 		}
-		prev_page = page;
+		prev_zpdesc = zpdesc;
 	}
 }
 
@@ -996,7 +1031,7 @@ static struct zspage *alloc_zspage(struct zs_pool *pool,
 					gfp_t gfp)
 {
 	int i;
-	struct page *pages[ZS_MAX_PAGES_PER_ZSPAGE];
+	struct zpdesc *zpdescs[ZS_MAX_PAGES_PER_ZSPAGE];
 	struct zspage *zspage = cache_alloc_zspage(pool, gfp);
 
 	if (!zspage)
@@ -1006,25 +1041,25 @@ static struct zspage *alloc_zspage(struct zs_pool *pool,
 	migrate_lock_init(zspage);
 
 	for (i = 0; i < class->pages_per_zspage; i++) {
-		struct page *page;
+		struct zpdesc *zpdesc;
 
-		page = alloc_page(gfp);
-		if (!page) {
+		zpdesc = alloc_zpdesc(gfp);
+		if (!zpdesc) {
 			while (--i >= 0) {
-				dec_zone_page_state(pages[i], NR_ZSPAGES);
-				__ClearPageZsmalloc(pages[i]);
-				__free_page(pages[i]);
+				zpdesc_dec_zone_page_state(zpdescs[i]);
+				__ClearPageZsmalloc(zpdesc_page(zpdescs[i]));
+				free_zpdesc(zpdescs[i]);
 			}
 			cache_free_zspage(pool, zspage);
 			return NULL;
 		}
-		__SetPageZsmalloc(page);
+		__SetPageZsmalloc(zpdesc_page(zpdesc));
 
-		inc_zone_page_state(page, NR_ZSPAGES);
-		pages[i] = page;
+		zpdesc_inc_zone_page_state(zpdesc);
+		zpdescs[i] = zpdesc;
 	}
 
-	create_page_chain(class, zspage, pages);
+	create_page_chain(class, zspage, zpdescs);
 	init_zspage(class, zspage);
 	zspage->pool = pool;
 	zspage->class = class->index;
@@ -1758,26 +1793,28 @@ static void migrate_write_unlock(struct zspage *zspage)
 static const struct movable_operations zsmalloc_mops;
 
 static void replace_sub_page(struct size_class *class, struct zspage *zspage,
-				struct page *newpage, struct page *oldpage)
+				struct zpdesc *newzpdesc, struct zpdesc *oldzpdesc)
 {
-	struct page *page;
-	struct page *pages[ZS_MAX_PAGES_PER_ZSPAGE] = {NULL, };
+	struct zpdesc *zpdesc;
+	struct zpdesc *zpdescs[ZS_MAX_PAGES_PER_ZSPAGE] = {NULL, };
+	unsigned int first_obj_offset;
 	int idx = 0;
 
-	page = get_first_page(zspage);
+	zpdesc = get_first_zpdesc(zspage);
 	do {
-		if (page == oldpage)
-			pages[idx] = newpage;
+		if (zpdesc == oldzpdesc)
+			zpdescs[idx] = newzpdesc;
 		else
-			pages[idx] = page;
+			zpdescs[idx] = zpdesc;
 		idx++;
-	} while ((page = get_next_page(page)) != NULL);
+	} while ((zpdesc = get_next_zpdesc(zpdesc)) != NULL);
 
-	create_page_chain(class, zspage, pages);
-	set_first_obj_offset(newpage, get_first_obj_offset(oldpage));
+	create_page_chain(class, zspage, zpdescs);
+	first_obj_offset = get_first_obj_offset(zpdesc_page(oldzpdesc));
+	set_first_obj_offset(zpdesc_page(newzpdesc), first_obj_offset);
 	if (unlikely(ZsHugePage(zspage)))
-		newpage->index = oldpage->index;
-	__SetPageMovable(newpage, &zsmalloc_mops);
+		newzpdesc->handle = oldzpdesc->handle;
+	__zpdesc_set_movable(newzpdesc, &zsmalloc_mops);
 }
 
 static bool zs_page_isolate(struct page *page, isolate_mode_t mode)
@@ -1850,7 +1887,7 @@ static int zs_page_migrate(struct page *newpage, struct page *page,
 	}
 	kunmap_atomic(s_addr);
 
-	replace_sub_page(class, zspage, newpage, page);
+	replace_sub_page(class, zspage, page_zpdesc(newpage), page_zpdesc(page));
 	/*
 	 * Since we complete the data copy and set up new zspage structure,
 	 * it's okay to release migration_lock.
-- 
2.43.0

[PATCH 07/20] mm/zsmalloc: convert obj_allocated() and related helpers to use zpdesc

[alexs]

From: Hyeonggon Yoo <42.hyeyoo@gmail.com>

Convert obj_allocated(), and related helpers to take zpdesc. Also make
its callers to cast (struct page *) to (struct zpdesc *) when calling them.
The users will be converted gradually as there are many.

Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Alex Shi <alexs@kernel.org>
---
 mm/zsmalloc.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index ee890d513f6f..6efaa6279687 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -847,15 +847,15 @@ static unsigned long handle_to_obj(unsigned long handle)
 	return *(unsigned long *)handle;
 }
 
-static inline bool obj_allocated(struct page *page, void *obj,
+static inline bool obj_allocated(struct zpdesc *zpdesc, void *obj,
 				 unsigned long *phandle)
 {
 	unsigned long handle;
-	struct zspage *zspage = get_zspage(page);
+	struct zspage *zspage = get_zspage(zpdesc_page(zpdesc));
 
 	if (unlikely(ZsHugePage(zspage))) {
-		VM_BUG_ON_PAGE(!is_first_page(page), page);
-		handle = page->index;
+		VM_BUG_ON_PAGE(!is_first_zpdesc(zpdesc), zpdesc_page(zpdesc));
+		handle = zpdesc->handle;
 	} else
 		handle = *(unsigned long *)obj;
 
@@ -1607,18 +1607,18 @@ static void zs_object_copy(struct size_class *class, unsigned long dst,
  * return handle.
  */
 static unsigned long find_alloced_obj(struct size_class *class,
-				      struct page *page, int *obj_idx)
+				      struct zpdesc *zpdesc, int *obj_idx)
 {
 	unsigned int offset;
 	int index = *obj_idx;
 	unsigned long handle = 0;
-	void *addr = kmap_atomic(page);
+	void *addr = zpdesc_kmap_atomic(zpdesc);
 
-	offset = get_first_obj_offset(page);
+	offset = get_first_obj_offset(zpdesc_page(zpdesc));
 	offset += class->size * index;
 
 	while (offset < PAGE_SIZE) {
-		if (obj_allocated(page, addr + offset, &handle))
+		if (obj_allocated(zpdesc, addr + offset, &handle))
 			break;
 
 		offset += class->size;
@@ -1642,7 +1642,7 @@ static void migrate_zspage(struct zs_pool *pool, struct zspage *src_zspage,
 	struct size_class *class = pool->size_class[src_zspage->class];
 
 	while (1) {
-		handle = find_alloced_obj(class, s_page, &obj_idx);
+		handle = find_alloced_obj(class, page_zpdesc(s_page), &obj_idx);
 		if (!handle) {
 			s_page = get_next_page(s_page);
 			if (!s_page)
@@ -1876,7 +1876,7 @@ static int zs_page_migrate(struct page *newpage, struct page *page,
 
 	for (addr = s_addr + offset; addr < s_addr + PAGE_SIZE;
 					addr += class->size) {
-		if (obj_allocated(page, addr, &handle)) {
+		if (obj_allocated(page_zpdesc(page), addr, &handle)) {
 
 			old_obj = handle_to_obj(handle);
 			obj_to_location(old_obj, &dummy, &obj_idx);
-- 
2.43.0

[PATCH 08/20] mm/zsmalloc: convert init_zspage() to use zpdesc

[alexs]

From: Hyeonggon Yoo <42.hyeyoo@gmail.com>

Replace get_first/next_page func series and kmap_atomic to new helper,
no functional change.

Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Alex Shi <alexs@kernel.org>
---
 mm/zsmalloc.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 6efaa6279687..e90e3a638068 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -950,16 +950,16 @@ static void init_zspage(struct size_class *class, struct zspage *zspage)
 {
 	unsigned int freeobj = 1;
 	unsigned long off = 0;
-	struct page *page = get_first_page(zspage);
+	struct zpdesc *zpdesc = get_first_zpdesc(zspage);
 
-	while (page) {
-		struct page *next_page;
+	while (zpdesc) {
+		struct zpdesc *next_zpdesc;
 		struct link_free *link;
 		void *vaddr;
 
-		set_first_obj_offset(page, off);
+		set_first_obj_offset(zpdesc_page(zpdesc), off);
 
-		vaddr = kmap_atomic(page);
+		vaddr = zpdesc_kmap_atomic(zpdesc);
 		link = (struct link_free *)vaddr + off / sizeof(*link);
 
 		while ((off += class->size) < PAGE_SIZE) {
@@ -972,8 +972,8 @@ static void init_zspage(struct size_class *class, struct zspage *zspage)
 		 * page, which must point to the first object on the next
 		 * page (if present)
 		 */
-		next_page = get_next_page(page);
-		if (next_page) {
+		next_zpdesc = get_next_zpdesc(zpdesc);
+		if (next_zpdesc) {
 			link->next = freeobj++ << OBJ_TAG_BITS;
 		} else {
 			/*
@@ -983,7 +983,7 @@ static void init_zspage(struct size_class *class, struct zspage *zspage)
 			link->next = -1UL << OBJ_TAG_BITS;
 		}
 		kunmap_atomic(vaddr);
-		page = next_page;
+		zpdesc = next_zpdesc;
 		off %= PAGE_SIZE;
 	}
 
-- 
2.43.0

[PATCH 09/20] mm/zsmalloc: convert obj_to_page() and zs_free() to use zpdesc

[alexs]

From: Hyeonggon Yoo <42.hyeyoo@gmail.com>

Rename obj_to_page() to obj_to_zpdesc() and also convert it and
its user zs_free() to use zpdesc.

Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Alex Shi <alexs@kernel.org>
---
 mm/zsmalloc.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index e90e3a638068..3ef8e13fb9e6 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -822,9 +822,9 @@ static void obj_to_location(unsigned long obj, struct zpdesc **zpdesc,
 	*obj_idx = (obj & OBJ_INDEX_MASK);
 }
 
-static void obj_to_page(unsigned long obj, struct page **page)
+static void obj_to_zpdesc(unsigned long obj, struct zpdesc **zpdesc)
 {
-	*page = pfn_to_page(obj >> OBJ_INDEX_BITS);
+	*zpdesc = pfn_zpdesc(obj >> OBJ_INDEX_BITS);
 }
 
 /**
@@ -1500,7 +1500,7 @@ static void obj_free(int class_size, unsigned long obj)
 void zs_free(struct zs_pool *pool, unsigned long handle)
 {
 	struct zspage *zspage;
-	struct page *f_page;
+	struct zpdesc *f_zpdesc;
 	unsigned long obj;
 	struct size_class *class;
 	int fullness;
@@ -1514,8 +1514,8 @@ void zs_free(struct zs_pool *pool, unsigned long handle)
 	 */
 	read_lock(&pool->migrate_lock);
 	obj = handle_to_obj(handle);
-	obj_to_page(obj, &f_page);
-	zspage = get_zspage(f_page);
+	obj_to_zpdesc(obj, &f_zpdesc);
+	zspage = get_zspage(zpdesc_page(f_zpdesc));
 	class = zspage_class(pool, zspage);
 	spin_lock(&class->lock);
 	read_unlock(&pool->migrate_lock);
-- 
2.43.0

[PATCH 10/20] mm/zsmalloc: add zpdesc_is_isolated/zpdesc_zone helper for zs_page_migrate

[alexs]

From: Hyeonggon Yoo <42.hyeyoo@gmail.com>

To convert page to zpdesc in zs_page_migrate(), we added
zpdesc_is_isolated/zpdesc_zone helpers. No functional change.

Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Alex Shi <alexs@kernel.org>
---
 mm/zpdesc.h   | 11 +++++++++++
 mm/zsmalloc.c | 30 ++++++++++++++++--------------
 2 files changed, 27 insertions(+), 14 deletions(-)

diff --git a/mm/zpdesc.h b/mm/zpdesc.h
index f998d65c59d6..2e35b8220e05 100644
--- a/mm/zpdesc.h
+++ b/mm/zpdesc.h
@@ -98,4 +98,15 @@ static inline void __zpdesc_set_movable(struct zpdesc *zpdesc,
 {
 	__SetPageMovable(zpdesc_page(zpdesc), mops);
 }
+
+static inline bool zpdesc_is_isolated(struct zpdesc *zpdesc)
+{
+	return PageIsolated(zpdesc_page(zpdesc));
+}
+
+static inline struct zone *zpdesc_zone(struct zpdesc *zpdesc)
+{
+	return page_zone(zpdesc_page(zpdesc));
+}
+
 #endif
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 3ef8e13fb9e6..251a6e63e58a 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -1835,19 +1835,21 @@ static int zs_page_migrate(struct page *newpage, struct page *page,
 	struct size_class *class;
 	struct zspage *zspage;
 	struct zpdesc *dummy;
+	struct zpdesc *newzpdesc = page_zpdesc(newpage);
+	struct zpdesc *zpdesc = page_zpdesc(page);
 	void *s_addr, *d_addr, *addr;
 	unsigned int offset;
 	unsigned long handle;
 	unsigned long old_obj, new_obj;
 	unsigned int obj_idx;
 
-	VM_BUG_ON_PAGE(!PageIsolated(page), page);
+	VM_BUG_ON_PAGE(!zpdesc_is_isolated(zpdesc), zpdesc_page(zpdesc));
 
 	/* We're committed, tell the world that this is a Zsmalloc page. */
-	__SetPageZsmalloc(newpage);
+	__SetPageZsmalloc(zpdesc_page(newzpdesc));
 
 	/* The page is locked, so this pointer must remain valid */
-	zspage = get_zspage(page);
+	zspage = get_zspage(zpdesc_page(zpdesc));
 	pool = zspage->pool;
 
 	/*
@@ -1864,30 +1866,30 @@ static int zs_page_migrate(struct page *newpage, struct page *page,
 	/* the migrate_write_lock protects zpage access via zs_map_object */
 	migrate_write_lock(zspage);
 
-	offset = get_first_obj_offset(page);
-	s_addr = kmap_atomic(page);
+	offset = get_first_obj_offset(zpdesc_page(zpdesc));
+	s_addr = zpdesc_kmap_atomic(zpdesc);
 
 	/*
 	 * Here, any user cannot access all objects in the zspage so let's move.
 	 */
-	d_addr = kmap_atomic(newpage);
+	d_addr = zpdesc_kmap_atomic(newzpdesc);
 	copy_page(d_addr, s_addr);
 	kunmap_atomic(d_addr);
 
 	for (addr = s_addr + offset; addr < s_addr + PAGE_SIZE;
 					addr += class->size) {
-		if (obj_allocated(page_zpdesc(page), addr, &handle)) {
+		if (obj_allocated(zpdesc, addr, &handle)) {
 
 			old_obj = handle_to_obj(handle);
 			obj_to_location(old_obj, &dummy, &obj_idx);
-			new_obj = (unsigned long)location_to_obj(newpage,
+			new_obj = (unsigned long)location_to_obj(zpdesc_page(newzpdesc),
 								obj_idx);
 			record_obj(handle, new_obj);
 		}
 	}
 	kunmap_atomic(s_addr);
 
-	replace_sub_page(class, zspage, page_zpdesc(newpage), page_zpdesc(page));
+	replace_sub_page(class, zspage, newzpdesc, zpdesc);
 	/*
 	 * Since we complete the data copy and set up new zspage structure,
 	 * it's okay to release migration_lock.
@@ -1896,14 +1898,14 @@ static int zs_page_migrate(struct page *newpage, struct page *page,
 	spin_unlock(&class->lock);
 	migrate_write_unlock(zspage);
 
-	get_page(newpage);
-	if (page_zone(newpage) != page_zone(page)) {
-		dec_zone_page_state(page, NR_ZSPAGES);
-		inc_zone_page_state(newpage, NR_ZSPAGES);
+	zpdesc_get(newzpdesc);
+	if (zpdesc_zone(newzpdesc) != zpdesc_zone(zpdesc)) {
+		zpdesc_dec_zone_page_state(zpdesc);
+		zpdesc_inc_zone_page_state(newzpdesc);
 	}
 
 	reset_page(page);
-	put_page(page);
+	zpdesc_put(zpdesc);
 
 	return MIGRATEPAGE_SUCCESS;
 }
-- 
2.43.0

[PATCH 11/20] mm/zsmalloc: rename reset_page to reset_zpdesc and use zpdesc in it

[alexs]

From: Alex Shi <alexs@kernel.org>

zpdesc.zspage matches with page.private, zpdesc.next matches with
page.index. They will be reset in reset_page() wich is called prior to
free base pages of a zspage.
Use zpdesc to replace page struct and rename it to reset_zpdesc(), few
page helper still left since they are used too widely.

Signed-off-by: Alex Shi <alexs@kernel.org>
---
 mm/zsmalloc.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 251a6e63e58a..216f8e6950ef 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -867,12 +867,14 @@ static inline bool obj_allocated(struct zpdesc *zpdesc, void *obj,
 	return true;
 }
 
-static void reset_page(struct page *page)
+static void reset_zpdesc(struct zpdesc *zpdesc)
 {
+	struct page *page = zpdesc_page(zpdesc);
+
 	__ClearPageMovable(page);
 	ClearPagePrivate(page);
-	set_page_private(page, 0);
-	page->index = 0;
+	zpdesc->zspage = NULL;
+	zpdesc->next = NULL;
 	reset_first_obj_offset(page);
 	__ClearPageZsmalloc(page);
 }
@@ -912,7 +914,7 @@ static void __free_zspage(struct zs_pool *pool, struct size_class *class,
 	do {
 		VM_BUG_ON_PAGE(!PageLocked(page), page);
 		next = get_next_page(page);
-		reset_page(page);
+		reset_zpdesc(page_zpdesc(page));
 		unlock_page(page);
 		dec_zone_page_state(page, NR_ZSPAGES);
 		put_page(page);
@@ -1904,7 +1906,7 @@ static int zs_page_migrate(struct page *newpage, struct page *page,
 		zpdesc_inc_zone_page_state(newzpdesc);
 	}
 
-	reset_page(page);
+	reset_zpdesc(zpdesc);
 	zpdesc_put(zpdesc);
 
 	return MIGRATEPAGE_SUCCESS;
-- 
2.43.0

[PATCH 12/20] mm/zsmalloc: convert __free_zspage() to use zdsesc

[alexs]

From: Hyeonggon Yoo <42.hyeyoo@gmail.com>

Introduce zpdesc_is_locked() and convert __free_zspage() to use zpdesc.

Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Alex Shi <alexs@kernel.org>
---
 mm/zpdesc.h   |  4 ++++
 mm/zsmalloc.c | 20 ++++++++++----------
 2 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/mm/zpdesc.h b/mm/zpdesc.h
index 2e35b8220e05..186ff9711ffb 100644
--- a/mm/zpdesc.h
+++ b/mm/zpdesc.h
@@ -109,4 +109,8 @@ static inline struct zone *zpdesc_zone(struct zpdesc *zpdesc)
 	return page_zone(zpdesc_page(zpdesc));
 }
 
+static inline bool zpdesc_is_locked(struct zpdesc *zpdesc)
+{
+	return PageLocked(zpdesc_page(zpdesc));
+}
 #endif
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 216f8e6950ef..bf5a1b63bb17 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -903,23 +903,23 @@ static int trylock_zspage(struct zspage *zspage)
 static void __free_zspage(struct zs_pool *pool, struct size_class *class,
 				struct zspage *zspage)
 {
-	struct page *page, *next;
+	struct zpdesc *zpdesc, *next;
 
 	assert_spin_locked(&class->lock);
 
 	VM_BUG_ON(get_zspage_inuse(zspage));
 	VM_BUG_ON(zspage->fullness != ZS_INUSE_RATIO_0);
 
-	next = page = get_first_page(zspage);
+	next = zpdesc = get_first_zpdesc(zspage);
 	do {
-		VM_BUG_ON_PAGE(!PageLocked(page), page);
-		next = get_next_page(page);
-		reset_zpdesc(page_zpdesc(page));
-		unlock_page(page);
-		dec_zone_page_state(page, NR_ZSPAGES);
-		put_page(page);
-		page = next;
-	} while (page != NULL);
+		VM_BUG_ON_PAGE(!zpdesc_is_locked(zpdesc), zpdesc_page(zpdesc));
+		next = get_next_zpdesc(zpdesc);
+		reset_zpdesc(zpdesc);
+		zpdesc_unlock(zpdesc);
+		zpdesc_dec_zone_page_state(zpdesc);
+		zpdesc_put(zpdesc);
+		zpdesc = next;
+	} while (zpdesc != NULL);
 
 	cache_free_zspage(pool, zspage);
 
-- 
2.43.0

[PATCH 13/20] mm/zsmalloc: convert location_to_obj() to take zpdesc

[alexs]

From: Hyeonggon Yoo <42.hyeyoo@gmail.com>

As all users of location_to_obj() now use zpdesc, convert
location_to_obj() to take zpdesc.

Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Alex Shi <alexs@kernel.org>
---
 mm/zsmalloc.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index bf5a1b63bb17..e8af01768ae0 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -828,15 +828,15 @@ static void obj_to_zpdesc(unsigned long obj, struct zpdesc **zpdesc)
 }
 
 /**
- * location_to_obj - get obj value encoded from (<page>, <obj_idx>)
- * @page: page object resides in zspage
+ * location_to_obj - get obj value encoded from (<zpdesc>, <obj_idx>)
+ * @zpdesc: zpdesc object resides in zspage
  * @obj_idx: object index
  */
-static unsigned long location_to_obj(struct page *page, unsigned int obj_idx)
+static unsigned long location_to_obj(struct zpdesc *zpdesc, unsigned int obj_idx)
 {
 	unsigned long obj;
 
-	obj = page_to_pfn(page) << OBJ_INDEX_BITS;
+	obj = zpdesc_pfn(zpdesc) << OBJ_INDEX_BITS;
 	obj |= obj_idx & OBJ_INDEX_MASK;
 
 	return obj;
@@ -1395,7 +1395,7 @@ static unsigned long obj_malloc(struct zs_pool *pool,
 	kunmap_atomic(vaddr);
 	mod_zspage_inuse(zspage, 1);
 
-	obj = location_to_obj(zpdesc_page(m_zpdesc), obj);
+	obj = location_to_obj(m_zpdesc, obj);
 
 	return obj;
 }
@@ -1884,8 +1884,7 @@ static int zs_page_migrate(struct page *newpage, struct page *page,
 
 			old_obj = handle_to_obj(handle);
 			obj_to_location(old_obj, &dummy, &obj_idx);
-			new_obj = (unsigned long)location_to_obj(zpdesc_page(newzpdesc),
-								obj_idx);
+			new_obj = (unsigned long)location_to_obj(newzpdesc, obj_idx);
 			record_obj(handle, new_obj);
 		}
 	}
-- 
2.43.0

[PATCH 14/20] mm/zsmalloc: convert migrate_zspage() to use zpdesc

[alexs]

From: Hyeonggon Yoo <42.hyeyoo@gmail.com>

Use get_first_zpdesc/get_next_zpdesc to replace get_first/next_page. No
functional change.

Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Alex Shi <alexs@kernel.org>
---
 mm/zsmalloc.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index e8af01768ae0..a10af49d8d08 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -1640,14 +1640,14 @@ static void migrate_zspage(struct zs_pool *pool, struct zspage *src_zspage,
 	unsigned long used_obj, free_obj;
 	unsigned long handle;
 	int obj_idx = 0;
-	struct page *s_page = get_first_page(src_zspage);
+	struct zpdesc *s_zpdesc = get_first_zpdesc(src_zspage);
 	struct size_class *class = pool->size_class[src_zspage->class];
 
 	while (1) {
-		handle = find_alloced_obj(class, page_zpdesc(s_page), &obj_idx);
+		handle = find_alloced_obj(class, s_zpdesc, &obj_idx);
 		if (!handle) {
-			s_page = get_next_page(s_page);
-			if (!s_page)
+			s_zpdesc = get_next_zpdesc(s_zpdesc);
+			if (!s_zpdesc)
 				break;
 			obj_idx = 0;
 			continue;
-- 
2.43.0

[PATCH 15/20] mm/zsmalloc: convert get_zspage() to take zpdesc

[alexs]

From: Hyeonggon Yoo <42.hyeyoo@gmail.com>

Now that all users except get_next_page() (which will be removed in
later patch) use zpdesc, convert get_zspage() to take zpdesc instead
of page.

Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Alex Shi <alexs@kernel.org>
---
 mm/zsmalloc.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index a10af49d8d08..c136124adb10 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -781,9 +781,9 @@ static int fix_fullness_group(struct size_class *class, struct zspage *zspage)
 	return newfg;
 }
 
-static struct zspage *get_zspage(struct page *page)
+static struct zspage *get_zspage(struct zpdesc *zpdesc)
 {
-	struct zspage *zspage = (struct zspage *)page_private(page);
+	struct zspage *zspage = zpdesc->zspage;
 
 	BUG_ON(zspage->magic != ZSPAGE_MAGIC);
 	return zspage;
@@ -791,7 +791,7 @@ static struct zspage *get_zspage(struct page *page)
 
 static struct page *get_next_page(struct page *page)
 {
-	struct zspage *zspage = get_zspage(page);
+	struct zspage *zspage = get_zspage(page_zpdesc(page));
 
 	if (unlikely(ZsHugePage(zspage)))
 		return NULL;
@@ -801,7 +801,7 @@ static struct page *get_next_page(struct page *page)
 
 static struct zpdesc *get_next_zpdesc(struct zpdesc *zpdesc)
 {
-	struct zspage *zspage = get_zspage(zpdesc_page(zpdesc));
+	struct zspage *zspage = get_zspage(zpdesc);
 
 	if (unlikely(ZsHugePage(zspage)))
 		return NULL;
@@ -851,7 +851,7 @@ static inline bool obj_allocated(struct zpdesc *zpdesc, void *obj,
 				 unsigned long *phandle)
 {
 	unsigned long handle;
-	struct zspage *zspage = get_zspage(zpdesc_page(zpdesc));
+	struct zspage *zspage = get_zspage(zpdesc);
 
 	if (unlikely(ZsHugePage(zspage))) {
 		VM_BUG_ON_PAGE(!is_first_zpdesc(zpdesc), zpdesc_page(zpdesc));
@@ -1267,7 +1267,7 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
 	read_lock(&pool->migrate_lock);
 	obj = handle_to_obj(handle);
 	obj_to_location(obj, &zpdesc, &obj_idx);
-	zspage = get_zspage(zpdesc_page(zpdesc));
+	zspage = get_zspage(zpdesc);
 
 	/*
 	 * migration cannot move any zpages in this zspage. Here, class->lock
@@ -1317,7 +1317,7 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
 
 	obj = handle_to_obj(handle);
 	obj_to_location(obj, &zpdesc, &obj_idx);
-	zspage = get_zspage(zpdesc_page(zpdesc));
+	zspage = get_zspage(zpdesc);
 	class = zspage_class(pool, zspage);
 	off = offset_in_page(class->size * obj_idx);
 
@@ -1483,7 +1483,7 @@ static void obj_free(int class_size, unsigned long obj)
 
 	obj_to_location(obj, &f_zpdesc, &f_objidx);
 	f_offset = offset_in_page(class_size * f_objidx);
-	zspage = get_zspage(zpdesc_page(f_zpdesc));
+	zspage = get_zspage(f_zpdesc);
 
 	vaddr = zpdesc_kmap_atomic(f_zpdesc);
 	link = (struct link_free *)(vaddr + f_offset);
@@ -1517,7 +1517,7 @@ void zs_free(struct zs_pool *pool, unsigned long handle)
 	read_lock(&pool->migrate_lock);
 	obj = handle_to_obj(handle);
 	obj_to_zpdesc(obj, &f_zpdesc);
-	zspage = get_zspage(zpdesc_page(f_zpdesc));
+	zspage = get_zspage(f_zpdesc);
 	class = zspage_class(pool, zspage);
 	spin_lock(&class->lock);
 	read_unlock(&pool->migrate_lock);
@@ -1851,7 +1851,7 @@ static int zs_page_migrate(struct page *newpage, struct page *page,
 	__SetPageZsmalloc(zpdesc_page(newzpdesc));
 
 	/* The page is locked, so this pointer must remain valid */
-	zspage = get_zspage(zpdesc_page(zpdesc));
+	zspage = get_zspage(zpdesc);
 	pool = zspage->pool;
 
 	/*
-- 
2.43.0

[PATCH 16/20] mm/zsmalloc: convert SetZsPageMovable and remove unused funcs

[alexs]

From: Alex Shi <alexs@kernel.org>

Convert SetZsPageMovable() to use zpdesc, and then remove unused
funcs:get_next_page/get_first_page/is_first_page.

Originally-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Alex Shi <alexs@kernel.org>
---
 mm/zsmalloc.c | 33 +++++----------------------------
 1 file changed, 5 insertions(+), 28 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index c136124adb10..951292dbcae4 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -470,11 +470,6 @@ static DEFINE_PER_CPU(struct mapping_area, zs_map_area) = {
 	.lock	= INIT_LOCAL_LOCK(lock),
 };
 
-static __maybe_unused int is_first_page(struct page *page)
-{
-	return PagePrivate(page);
-}
-
 static int is_first_zpdesc(struct zpdesc *zpdesc)
 {
 	return PagePrivate(zpdesc_page(zpdesc));
@@ -491,14 +486,6 @@ static inline void mod_zspage_inuse(struct zspage *zspage, int val)
 	zspage->inuse += val;
 }
 
-static inline struct page *get_first_page(struct zspage *zspage)
-{
-	struct page *first_page = zpdesc_page(zspage->first_zpdesc);
-
-	VM_BUG_ON_PAGE(!is_first_page(first_page), first_page);
-	return first_page;
-}
-
 static struct zpdesc *get_first_zpdesc(struct zspage *zspage)
 {
 	struct zpdesc *first_zpdesc = zspage->first_zpdesc;
@@ -789,16 +776,6 @@ static struct zspage *get_zspage(struct zpdesc *zpdesc)
 	return zspage;
 }
 
-static struct page *get_next_page(struct page *page)
-{
-	struct zspage *zspage = get_zspage(page_zpdesc(page));
-
-	if (unlikely(ZsHugePage(zspage)))
-		return NULL;
-
-	return (struct page *)page->index;
-}
-
 static struct zpdesc *get_next_zpdesc(struct zpdesc *zpdesc)
 {
 	struct zspage *zspage = get_zspage(zpdesc);
@@ -1974,13 +1951,13 @@ static void init_deferred_free(struct zs_pool *pool)
 
 static void SetZsPageMovable(struct zs_pool *pool, struct zspage *zspage)
 {
-	struct page *page = get_first_page(zspage);
+	struct zpdesc *zpdesc = get_first_zpdesc(zspage);
 
 	do {
-		WARN_ON(!trylock_page(page));
-		__SetPageMovable(page, &zsmalloc_mops);
-		unlock_page(page);
-	} while ((page = get_next_page(page)) != NULL);
+		WARN_ON(!zpdesc_trylock(zpdesc));
+		__zpdesc_set_movable(zpdesc, &zsmalloc_mops);
+		zpdesc_unlock(zpdesc);
+	} while ((zpdesc = get_next_zpdesc(zpdesc)) != NULL);
 }
 #else
 static inline void zs_flush_migration(struct zs_pool *pool) { }
-- 
2.43.0

[PATCH 17/20] mm/zsmalloc: convert get/set_first_obj_offset() to take zpdesc

[alexs]

From: Hyeonggon Yoo <42.hyeyoo@gmail.com>

Now that all users of get/set_first_obj_offset() are converted
to use zpdesc, convert them to take zpdesc.

Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Alex Shi <alexs@kernel.org>
---
 mm/zpdesc.h   |  3 +++
 mm/zsmalloc.c | 32 ++++++++++++++++----------------
 2 files changed, 19 insertions(+), 16 deletions(-)

diff --git a/mm/zpdesc.h b/mm/zpdesc.h
index 186ff9711ffb..17941774c46e 100644
--- a/mm/zpdesc.h
+++ b/mm/zpdesc.h
@@ -14,6 +14,7 @@
  * @next:		Next zpdesc in a zspage in zsmalloc zpool
  * @handle:		For huge zspage in zsmalloc zpool
  * @zspage:		Pointer to zspage in zsmalloc
+ * @first_obj_offset:	First object offset in zsmalloc zpool
  *
  * This struct overlays struct page for now. Do not modify without a good
  * understanding of the issues.
@@ -29,6 +30,7 @@ struct zpdesc {
 		unsigned long handle;
 	};
 	struct zspage *zspage;
+	unsigned int first_obj_offset;
 };
 #define ZPDESC_MATCH(pg, zp) \
 	static_assert(offsetof(struct page, pg) == offsetof(struct zpdesc, zp))
@@ -38,6 +40,7 @@ ZPDESC_MATCH(lru, lru);
 ZPDESC_MATCH(index, next);
 ZPDESC_MATCH(index, handle);
 ZPDESC_MATCH(private, zspage);
+ZPDESC_MATCH(page_type, first_obj_offset);
 #undef ZPDESC_MATCH
 static_assert(sizeof(struct zpdesc) <= sizeof(struct page));
 
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 951292dbcae4..3ce49f0372cc 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -496,26 +496,26 @@ static struct zpdesc *get_first_zpdesc(struct zspage *zspage)
 
 #define FIRST_OBJ_PAGE_TYPE_MASK	0xffff
 
-static inline void reset_first_obj_offset(struct page *page)
+static inline void reset_first_obj_offset(struct zpdesc *zpdesc)
 {
-	VM_WARN_ON_ONCE(!PageZsmalloc(page));
-	page->page_type |= FIRST_OBJ_PAGE_TYPE_MASK;
+	VM_WARN_ON_ONCE(!PageZsmalloc(zpdesc_page(zpdesc)));
+	zpdesc->first_obj_offset |= FIRST_OBJ_PAGE_TYPE_MASK;
 }
 
-static inline unsigned int get_first_obj_offset(struct page *page)
+static inline unsigned int get_first_obj_offset(struct zpdesc *zpdesc)
 {
-	VM_WARN_ON_ONCE(!PageZsmalloc(page));
-	return page->page_type & FIRST_OBJ_PAGE_TYPE_MASK;
+	VM_WARN_ON_ONCE(!PageZsmalloc(zpdesc_page(zpdesc)));
+	return zpdesc->first_obj_offset & FIRST_OBJ_PAGE_TYPE_MASK;
 }
 
-static inline void set_first_obj_offset(struct page *page, unsigned int offset)
+static inline void set_first_obj_offset(struct zpdesc *zpdesc, unsigned int offset)
 {
 	/* With 16 bit available, we can support offsets into 64 KiB pages. */
 	BUILD_BUG_ON(PAGE_SIZE > SZ_64K);
-	VM_WARN_ON_ONCE(!PageZsmalloc(page));
+	VM_WARN_ON_ONCE(!PageZsmalloc(zpdesc_page(zpdesc)));
 	VM_WARN_ON_ONCE(offset & ~FIRST_OBJ_PAGE_TYPE_MASK);
-	page->page_type &= ~FIRST_OBJ_PAGE_TYPE_MASK;
-	page->page_type |= offset & FIRST_OBJ_PAGE_TYPE_MASK;
+	zpdesc->first_obj_offset &= ~FIRST_OBJ_PAGE_TYPE_MASK;
+	zpdesc->first_obj_offset |= offset & FIRST_OBJ_PAGE_TYPE_MASK;
 }
 
 static inline unsigned int get_freeobj(struct zspage *zspage)
@@ -852,7 +852,7 @@ static void reset_zpdesc(struct zpdesc *zpdesc)
 	ClearPagePrivate(page);
 	zpdesc->zspage = NULL;
 	zpdesc->next = NULL;
-	reset_first_obj_offset(page);
+	reset_first_obj_offset(zpdesc);
 	__ClearPageZsmalloc(page);
 }
 
@@ -936,7 +936,7 @@ static void init_zspage(struct size_class *class, struct zspage *zspage)
 		struct link_free *link;
 		void *vaddr;
 
-		set_first_obj_offset(zpdesc_page(zpdesc), off);
+		set_first_obj_offset(zpdesc, off);
 
 		vaddr = zpdesc_kmap_atomic(zpdesc);
 		link = (struct link_free *)vaddr + off / sizeof(*link);
@@ -1593,7 +1593,7 @@ static unsigned long find_alloced_obj(struct size_class *class,
 	unsigned long handle = 0;
 	void *addr = zpdesc_kmap_atomic(zpdesc);
 
-	offset = get_first_obj_offset(zpdesc_page(zpdesc));
+	offset = get_first_obj_offset(zpdesc);
 	offset += class->size * index;
 
 	while (offset < PAGE_SIZE) {
@@ -1789,8 +1789,8 @@ static void replace_sub_page(struct size_class *class, struct zspage *zspage,
 	} while ((zpdesc = get_next_zpdesc(zpdesc)) != NULL);
 
 	create_page_chain(class, zspage, zpdescs);
-	first_obj_offset = get_first_obj_offset(zpdesc_page(oldzpdesc));
-	set_first_obj_offset(zpdesc_page(newzpdesc), first_obj_offset);
+	first_obj_offset = get_first_obj_offset(oldzpdesc);
+	set_first_obj_offset(newzpdesc, first_obj_offset);
 	if (unlikely(ZsHugePage(zspage)))
 		newzpdesc->handle = oldzpdesc->handle;
 	__zpdesc_set_movable(newzpdesc, &zsmalloc_mops);
@@ -1845,7 +1845,7 @@ static int zs_page_migrate(struct page *newpage, struct page *page,
 	/* the migrate_write_lock protects zpage access via zs_map_object */
 	migrate_write_lock(zspage);
 
-	offset = get_first_obj_offset(zpdesc_page(zpdesc));
+	offset = get_first_obj_offset(zpdesc);
 	s_addr = zpdesc_kmap_atomic(zpdesc);
 
 	/*
-- 
2.43.0

[PATCH 18/20] mm/zsmalloc: introduce __zpdesc_clear_movable

[alexs]

From: Alex Shi <alexs@kernel.org>

Add a helper __zpdesc_clear_movable() for __ClearPageMovable(), and use it
in callers to make code clear.

Signed-off-by: Alex Shi <alexs@kernel.org>
---
 mm/zpdesc.h   | 5 +++++
 mm/zsmalloc.c | 2 +-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/zpdesc.h b/mm/zpdesc.h
index 17941774c46e..c6a44fe04f97 100644
--- a/mm/zpdesc.h
+++ b/mm/zpdesc.h
@@ -102,6 +102,11 @@ static inline void __zpdesc_set_movable(struct zpdesc *zpdesc,
 	__SetPageMovable(zpdesc_page(zpdesc), mops);
 }
 
+static inline void __zpdesc_clear_movable(struct zpdesc *zpdesc)
+{
+	__ClearPageMovable(zpdesc_page(zpdesc));
+}
+
 static inline bool zpdesc_is_isolated(struct zpdesc *zpdesc)
 {
 	return PageIsolated(zpdesc_page(zpdesc));
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 3ce49f0372cc..abecc8a5c566 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -848,7 +848,7 @@ static void reset_zpdesc(struct zpdesc *zpdesc)
 {
 	struct page *page = zpdesc_page(zpdesc);
 
-	__ClearPageMovable(page);
+	__zpdesc_clear_movable(zpdesc);
 	ClearPagePrivate(page);
 	zpdesc->zspage = NULL;
 	zpdesc->next = NULL;
-- 
2.43.0

[PATCH 19/20] mm/zsmalloc: introduce __zpdesc_clear_zsmalloc

[alexs]

From: Alex Shi <alexs@kernel.org>

Add a helper __zpdesc_clear_zsmalloc() for __ClearPageZsmalloc(), and use
it in callers to make code clear.

Signed-off-by: Alex Shi <alexs@kernel.org>
---
 mm/zpdesc.h   | 5 +++++
 mm/zsmalloc.c | 4 ++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/mm/zpdesc.h b/mm/zpdesc.h
index c6a44fe04f97..e346b39aba59 100644
--- a/mm/zpdesc.h
+++ b/mm/zpdesc.h
@@ -107,6 +107,11 @@ static inline void __zpdesc_clear_movable(struct zpdesc *zpdesc)
 	__ClearPageMovable(zpdesc_page(zpdesc));
 }
 
+static inline void __zpdesc_clear_zsmalloc(struct zpdesc *zpdesc)
+{
+	__ClearPageZsmalloc(zpdesc_page(zpdesc));
+}
+
 static inline bool zpdesc_is_isolated(struct zpdesc *zpdesc)
 {
 	return PageIsolated(zpdesc_page(zpdesc));
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index abecc8a5c566..eaf8dad04f2c 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -853,7 +853,7 @@ static void reset_zpdesc(struct zpdesc *zpdesc)
 	zpdesc->zspage = NULL;
 	zpdesc->next = NULL;
 	reset_first_obj_offset(zpdesc);
-	__ClearPageZsmalloc(page);
+	__zpdesc_clear_zsmalloc(zpdesc);
 }
 
 static int trylock_zspage(struct zspage *zspage)
@@ -1026,7 +1026,7 @@ static struct zspage *alloc_zspage(struct zs_pool *pool,
 		if (!zpdesc) {
 			while (--i >= 0) {
 				zpdesc_dec_zone_page_state(zpdescs[i]);
-				__ClearPageZsmalloc(zpdesc_page(zpdescs[i]));
+				__zpdesc_clear_zsmalloc(zpdescs[i]);
 				free_zpdesc(zpdescs[i]);
 			}
 			cache_free_zspage(pool, zspage);
-- 
2.43.0

[PATCH 20/20] mm/zsmalloc: introduce __zpdesc_set_zsmalloc()

[alexs]

From: Alex Shi <alexs@kernel.org>

Add a helper __zpdesc_set_zsmalloc() for __SetPageZsmalloc(), and use
it in callers to make code clear.

Signed-off-by: Alex Shi <alexs@kernel.org>
---
 mm/zpdesc.h   | 5 +++++
 mm/zsmalloc.c | 4 ++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/mm/zpdesc.h b/mm/zpdesc.h
index e346b39aba59..ef36fc3de75d 100644
--- a/mm/zpdesc.h
+++ b/mm/zpdesc.h
@@ -107,6 +107,11 @@ static inline void __zpdesc_clear_movable(struct zpdesc *zpdesc)
 	__ClearPageMovable(zpdesc_page(zpdesc));
 }
 
+static inline void __zpdesc_set_zsmalloc(struct zpdesc *zpdesc)
+{
+	__SetPageZsmalloc(zpdesc_page(zpdesc));
+}
+
 static inline void __zpdesc_clear_zsmalloc(struct zpdesc *zpdesc)
 {
 	__ClearPageZsmalloc(zpdesc_page(zpdesc));
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index eaf8dad04f2c..e2a506f53957 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -1032,7 +1032,7 @@ static struct zspage *alloc_zspage(struct zs_pool *pool,
 			cache_free_zspage(pool, zspage);
 			return NULL;
 		}
-		__SetPageZsmalloc(zpdesc_page(zpdesc));
+		__zpdesc_set_zsmalloc(zpdesc);
 
 		zpdesc_inc_zone_page_state(zpdesc);
 		zpdescs[i] = zpdesc;
@@ -1825,7 +1825,7 @@ static int zs_page_migrate(struct page *newpage, struct page *page,
 	VM_BUG_ON_PAGE(!zpdesc_is_isolated(zpdesc), zpdesc_page(zpdesc));
 
 	/* We're committed, tell the world that this is a Zsmalloc page. */
-	__SetPageZsmalloc(zpdesc_page(newzpdesc));
+	__zpdesc_set_zsmalloc(newzpdesc);
 
 	/* The page is locked, so this pointer must remain valid */
 	zspage = get_zspage(zpdesc);
-- 
2.43.0

Re: [PATCH 00/20] mm/zsmalloc: add zpdesc memory descriptor for zswap.zpool

[Alex Shi]

On 6/28/24 11:11 AM, alexs@kernel.org wrote:
> From: Alex Shi <alexs@kernel.org>
> 
> According to Metthew's plan, the page descriptor will be replace by a 8
> bytes mem_desc on destination purpose.
> https://lore.kernel.org/lkml/YvV1KTyzZ+Jrtj9x@casper.infradead.org/
> 
> Here is a implement on zsmalloc to replace page descriptor by 'zpdesc',
> which is still overlay on struct page now. but it's a step move forward
> above destination.
> 
> To name the struct zpdesc instead of zsdesc, since there are still 3
> zpools under zswap: zbud, z3fold, zsmalloc for now(z3fold maybe removed
> soon), and we could easyly extend it to other zswap.zpool in needs.
> 
> For all zswap.zpools, they are all using single page since often used
> under memory pressure. So the conversion via folio series helper is
> better than page's for compound_head check saving.
> 
> For now, all zpools are using some page struct members, like page.flags
> for PG_private/PG_locked. and list_head lru, page.mapping for page migration.
> 
> This patachset could save 123Kbyetes zsmalloc.o size.

This patchset is based on next/mm-unstable.

Thanks
Alex

> 
> Thanks
> Alex
> 
> Alex Shi (8):
>   mm/zsmalloc: add zpdesc memory descriptor for zswap.zpool
>   mm/zsmalloc: use zpdesc in trylock_zspage/lock_zspage
>   mm/zsmalloc: convert create_page_chain() and its users to use zpdesc
>   mm/zsmalloc: rename reset_page to reset_zpdesc and use zpdesc in it
>   mm/zsmalloc: convert SetZsPageMovable and remove unused funcs
>   mm/zsmalloc: introduce __zpdesc_clear_movable
>   mm/zsmalloc: introduce __zpdesc_clear_zsmalloc
>   mm/zsmalloc: introduce __zpdesc_set_zsmalloc()
> 
> Hyeonggon Yoo (12):
>   mm/zsmalloc: convert __zs_map_object/__zs_unmap_object to use zpdesc
>   mm/zsmalloc: add and use pfn/zpdesc seeking funcs
>   mm/zsmalloc: convert obj_malloc() to use zpdesc
>   mm/zsmalloc: convert obj_allocated() and related helpers to use zpdesc
>   mm/zsmalloc: convert init_zspage() to use zpdesc
>   mm/zsmalloc: convert obj_to_page() and zs_free() to use zpdesc
>   mm/zsmalloc: add zpdesc_is_isolated/zpdesc_zone helper for
>     zs_page_migrate
>   mm/zsmalloc: convert __free_zspage() to use zdsesc
>   mm/zsmalloc: convert location_to_obj() to take zpdesc
>   mm/zsmalloc: convert migrate_zspage() to use zpdesc
>   mm/zsmalloc: convert get_zspage() to take zpdesc
>   mm/zsmalloc: convert get/set_first_obj_offset() to take zpdesc
> 
>  mm/zpdesc.h   | 134 +++++++++++++++
>  mm/zsmalloc.c | 454 +++++++++++++++++++++++++++-----------------------
>  2 files changed, 384 insertions(+), 204 deletions(-)
>  create mode 100644 mm/zpdesc.h
> 

Re: [PATCH 00/20] mm/zsmalloc: add zpdesc memory descriptor for zswap.zpool

[Alex Shi]

On 6/28/24 3:26 PM, Alex Shi wrote:
> 
> On 6/28/24 11:11 AM, alexs@kernel.org wrote:
>> From: Alex Shi <alexs@kernel.org>
>>
>> According to Metthew's plan, the page descriptor will be replace by a 8
>> bytes mem_desc on destination purpose.
>> https://lore.kernel.org/lkml/YvV1KTyzZ+Jrtj9x@casper.infradead.org/
>>
>> Here is a implement on zsmalloc to replace page descriptor by 'zpdesc',
>> which is still overlay on struct page now. but it's a step move forward
>> above destination.
>>
>> To name the struct zpdesc instead of zsdesc, since there are still 3
>> zpools under zswap: zbud, z3fold, zsmalloc for now(z3fold maybe removed
>> soon), and we could easyly extend it to other zswap.zpool in needs.
>>
>> For all zswap.zpools, they are all using single page since often used
>> under memory pressure. So the conversion via folio series helper is
>> better than page's for compound_head check saving.
>>
>> For now, all zpools are using some page struct members, like page.flags
>> for PG_private/PG_locked. and list_head lru, page.mapping for page migration.
>>
>> This patachset could save 123Kbyetes zsmalloc.o size.
> 
> This patchset is based on next/mm-unstable.

Sorry, just double checked, this patchset based on git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm mm-unstable branch. "4b17ce353e02 mm: optimization on page allocation when CMA enabled"

Thanks
Alex
> 
>>
>> Thanks
>> Alex
>>
>> Alex Shi (8):
>>   mm/zsmalloc: add zpdesc memory descriptor for zswap.zpool
>>   mm/zsmalloc: use zpdesc in trylock_zspage/lock_zspage
>>   mm/zsmalloc: convert create_page_chain() and its users to use zpdesc
>>   mm/zsmalloc: rename reset_page to reset_zpdesc and use zpdesc in it
>>   mm/zsmalloc: convert SetZsPageMovable and remove unused funcs
>>   mm/zsmalloc: introduce __zpdesc_clear_movable
>>   mm/zsmalloc: introduce __zpdesc_clear_zsmalloc
>>   mm/zsmalloc: introduce __zpdesc_set_zsmalloc()
>>
>> Hyeonggon Yoo (12):
>>   mm/zsmalloc: convert __zs_map_object/__zs_unmap_object to use zpdesc
>>   mm/zsmalloc: add and use pfn/zpdesc seeking funcs
>>   mm/zsmalloc: convert obj_malloc() to use zpdesc
>>   mm/zsmalloc: convert obj_allocated() and related helpers to use zpdesc
>>   mm/zsmalloc: convert init_zspage() to use zpdesc
>>   mm/zsmalloc: convert obj_to_page() and zs_free() to use zpdesc
>>   mm/zsmalloc: add zpdesc_is_isolated/zpdesc_zone helper for
>>     zs_page_migrate
>>   mm/zsmalloc: convert __free_zspage() to use zdsesc
>>   mm/zsmalloc: convert location_to_obj() to take zpdesc
>>   mm/zsmalloc: convert migrate_zspage() to use zpdesc
>>   mm/zsmalloc: convert get_zspage() to take zpdesc
>>   mm/zsmalloc: convert get/set_first_obj_offset() to take zpdesc
>>
>>  mm/zpdesc.h   | 134 +++++++++++++++
>>  mm/zsmalloc.c | 454 +++++++++++++++++++++++++++-----------------------
>>  2 files changed, 384 insertions(+), 204 deletions(-)
>>  create mode 100644 mm/zpdesc.h
>>

Re: [PATCH 01/20] mm/zsmalloc: add zpdesc memory descriptor for zswap.zpool

[Hyeonggon Yoo]

On Fri, Jun 28, 2024 at 12:06 PM <alexs@kernel.org> wrote:
>
> From: Alex Shi <alexs@kernel.org>
>
> The 1st patch introduces new memory decriptor zpdesc and rename
> zspage.first_page to zspage.first_zpdesc, no functional change.
>
> Originally-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
> Signed-off-by: Alex Shi <alexs@kernel.org>
> ---
>  mm/zpdesc.h   | 56 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  mm/zsmalloc.c | 19 ++++++++---------
>  2 files changed, 66 insertions(+), 9 deletions(-)
>  create mode 100644 mm/zpdesc.h

Hi Alex, thanks for your effort in pushing this forward!

> diff --git a/mm/zpdesc.h b/mm/zpdesc.h
> new file mode 100644
> index 000000000000..a1ab5ebaa936
> --- /dev/null
> +++ b/mm/zpdesc.h
> @@ -0,0 +1,56 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* zpdesc.h: zswap.zpool memory descriptor
> + *
> + * Written by Alex Shi <alexs@kernel.org>
> + *           Hyeonggon Yoo <42.hyeyoo@gmail.com>
> + */
> +#ifndef __MM_ZPDESC_H__
> +#define __MM_ZPDESC_H__
> +
> +/*
> + * struct zpdesc -     Memory descriptor for zpool memory, now is for zsmalloc
> + * @flags:             Page flags, PG_private: identifies the first component page
> + * @lru:               Indirected used by page migration

maybe Indirected -> Indirectly?

> + * @next:              Next zpdesc in a zspage in zsmalloc zpool
> + * @handle:            For huge zspage in zsmalloc zpool
> + * @zspage:            Pointer to zspage in zsmalloc
> + *
> + * This struct overlays struct page for now. Do not modify without a good
> + * understanding of the issues.
> + */
> +struct zpdesc {
> +       unsigned long flags;
> +       struct list_head lru;
> +       unsigned long _zp_pad_1;

for understanding, I think it'd be better to replace _zp_pad_1 with movable ops,
because mops reuses this 'mapping' field.

> +       union {
> +               /* Next zpdescs in a zspage in zsmalloc zpool */
> +               struct zpdesc *next;
> +               /* For huge zspage in zsmalloc zpool */
> +               unsigned long handle;
> +       };
> +       struct zspage *zspage;

There was a discussion with Yosry on including memcg_data on zpdesc
even if it's not used at the moment.

Maybe you can look at:
https://lore.kernel.org/linux-mm/CAB=+i9Quz9iP2-Lq=oQfKVVnzPDtOaKMm=hUPbnRg5hRxH+qaA@mail.gmail.com/

> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index fec1a39e5bbe..67bb80b7413a 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -13,17 +13,17 @@
>
>  /*
>   * Following is how we use various fields and flags of underlying
> - * struct page(s) to form a zspage.
> + * struct zpdesc(page) to form a zspage.
>   *
> - * Usage of struct page fields:
> - *     page->private: points to zspage
> - *     page->index: links together all component pages of a zspage
> + * Usage of struct zpdesc fields:
> + *     zpdesc->zspage: points to zspage
> + *     zpdesc->next: 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
>   *             offset in a subpage of a zspage
>   *
> - * Usage of struct page flags:
> + * Usage of struct zpdesc(page) flags:
>   *     PG_private: identifies the first component page
>   *     PG_owner_priv_1: identifies the huge component page

the comment for PG_owner_priv_1 can safely be removed as it's not used
after commit a41ec880aa7b ("zsmalloc: move huge compressed obj from
page to zspage")

> @@ -948,7 +949,7 @@ static void create_page_chain(struct size_class *class, struct zspage *zspage,
>                 set_page_private(page, (unsigned long)zspage);
>                 page->index = 0;
>                 if (i == 0) {
> -                       zspage->first_page = page;
> +                       zspage->first_zpdesc = page_zpdesc(page);
>                         SetPagePrivate(page);
>                         if (unlikely(class->objs_per_zspage == 1 &&
>                                         class->pages_per_zspage == 1))
> @@ -1325,7 +1326,7 @@ static unsigned long obj_malloc(struct zs_pool *pool,
>                 link->handle = handle;
>         else
>                 /* record handle to page->index */
> -               zspage->first_page->index = handle;
> +               zspage->first_zpdesc->handle = handle;

FYI this line seems to conflict with
bcc6116e39f512 ("mm/zsmalloc: move record_obj() into obj_malloc()")
on mm-unstable.

Best,
Hyeonggon

Re: [PATCH 01/20] mm/zsmalloc: add zpdesc memory descriptor for zswap.zpool

[Alex Shi]

On 6/30/24 9:45 PM, Hyeonggon Yoo wrote:
> On Fri, Jun 28, 2024 at 12:06 PM <alexs@kernel.org> wrote:
>>
>> From: Alex Shi <alexs@kernel.org>
>>
>> The 1st patch introduces new memory decriptor zpdesc and rename
>> zspage.first_page to zspage.first_zpdesc, no functional change.
>>
>> Originally-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
>> Signed-off-by: Alex Shi <alexs@kernel.org>
>> ---
>>  mm/zpdesc.h   | 56 +++++++++++++++++++++++++++++++++++++++++++++++++++
>>  mm/zsmalloc.c | 19 ++++++++---------
>>  2 files changed, 66 insertions(+), 9 deletions(-)
>>  create mode 100644 mm/zpdesc.h
> 
> Hi Alex, thanks for your effort in pushing this forward!
> 
>> diff --git a/mm/zpdesc.h b/mm/zpdesc.h
>> new file mode 100644
>> index 000000000000..a1ab5ebaa936
>> --- /dev/null
>> +++ b/mm/zpdesc.h
>> @@ -0,0 +1,56 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +/* zpdesc.h: zswap.zpool memory descriptor
>> + *
>> + * Written by Alex Shi <alexs@kernel.org>
>> + *           Hyeonggon Yoo <42.hyeyoo@gmail.com>
>> + */
>> +#ifndef __MM_ZPDESC_H__
>> +#define __MM_ZPDESC_H__
>> +
>> +/*
>> + * struct zpdesc -     Memory descriptor for zpool memory, now is for zsmalloc
>> + * @flags:             Page flags, PG_private: identifies the first component page
>> + * @lru:               Indirected used by page migration
> 
> maybe Indirected -> Indirectly?

Hi Yoo,

Thanks for comments! Yes Indirectly is better. I will update it in next version.

> 
>> + * @next:              Next zpdesc in a zspage in zsmalloc zpool
>> + * @handle:            For huge zspage in zsmalloc zpool
>> + * @zspage:            Pointer to zspage in zsmalloc
>> + *
>> + * This struct overlays struct page for now. Do not modify without a good
>> + * understanding of the issues.
>> + */
>> +struct zpdesc {
>> +       unsigned long flags;
>> +       struct list_head lru;
>> +       unsigned long _zp_pad_1;
> 
> for understanding, I think it'd be better to replace _zp_pad_1 with movable ops,
> because mops reuses this 'mapping' field.

Right, 'mops' looks a bit more clear.

> 
>> +       union {
>> +               /* Next zpdescs in a zspage in zsmalloc zpool */
>> +               struct zpdesc *next;
>> +               /* For huge zspage in zsmalloc zpool */
>> +               unsigned long handle;
>> +       };
>> +       struct zspage *zspage;
> 
> There was a discussion with Yosry on including memcg_data on zpdesc
> even if it's not used at the moment.
> 
> Maybe you can look at:
> https://lore.kernel.org/linux-mm/CAB=+i9Quz9iP2-Lq=oQfKVVnzPDtOaKMm=hUPbnRg5hRxH+qaA@mail.gmail.com/

Thanks for notice. 
The memcg_data isn't used for zpdesc. And I have a bit confusion since Yosry said: "I think to drop memcg_data we need to enlighten the code that ...". So we actually don't need to have this unused member, is this right, Yosry?

> 
>> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
>> index fec1a39e5bbe..67bb80b7413a 100644
>> --- a/mm/zsmalloc.c
>> +++ b/mm/zsmalloc.c
>> @@ -13,17 +13,17 @@
>>
>>  /*
>>   * Following is how we use various fields and flags of underlying
>> - * struct page(s) to form a zspage.
>> + * struct zpdesc(page) to form a zspage.
>>   *
>> - * Usage of struct page fields:
>> - *     page->private: points to zspage
>> - *     page->index: links together all component pages of a zspage
>> + * Usage of struct zpdesc fields:
>> + *     zpdesc->zspage: points to zspage
>> + *     zpdesc->next: 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
>>   *             offset in a subpage of a zspage
>>   *
>> - * Usage of struct page flags:
>> + * Usage of struct zpdesc(page) flags:
>>   *     PG_private: identifies the first component page
>>   *     PG_owner_priv_1: identifies the huge component page
> 
> the comment for PG_owner_priv_1 can safely be removed as it's not used
> after commit a41ec880aa7b ("zsmalloc: move huge compressed obj from
> page to zspage")

Right, thanks for info!

> 
>> @@ -948,7 +949,7 @@ static void create_page_chain(struct size_class *class, struct zspage *zspage,
>>                 set_page_private(page, (unsigned long)zspage);
>>                 page->index = 0;
>>                 if (i == 0) {
>> -                       zspage->first_page = page;
>> +                       zspage->first_zpdesc = page_zpdesc(page);
>>                         SetPagePrivate(page);
>>                         if (unlikely(class->objs_per_zspage == 1 &&
>>                                         class->pages_per_zspage == 1))
>> @@ -1325,7 +1326,7 @@ static unsigned long obj_malloc(struct zs_pool *pool,
>>                 link->handle = handle;
>>         else
>>                 /* record handle to page->index */
>> -               zspage->first_page->index = handle;
>> +               zspage->first_zpdesc->handle = handle;
> 
> FYI this line seems to conflict with
> bcc6116e39f512 ("mm/zsmalloc: move record_obj() into obj_malloc()")
> on mm-unstable.

yes, a new commit made this conflict. will update this in next version.

Thanks
Alex
> 
> Best,
> Hyeonggon

Re: [PATCH 01/20] mm/zsmalloc: add zpdesc memory descriptor for zswap.zpool

[Alex Shi]

Ops, 

Sorry for missing Yosry and Nhat. How stupid I am!
Here is the first patch on lore: https://lore.kernel.org/all/20240628031138.429622-1-alexs@kernel.org/

Sorry for this!
Alex

On 7/1/24 11:03 AM, Alex Shi wrote:
> 
> 
> On 6/30/24 9:45 PM, Hyeonggon Yoo wrote:
>> On Fri, Jun 28, 2024 at 12:06 PM <alexs@kernel.org> wrote:
>>>
>>> From: Alex Shi <alexs@kernel.org>
>>>
>>> The 1st patch introduces new memory decriptor zpdesc and rename
>>> zspage.first_page to zspage.first_zpdesc, no functional change.
>>>
>>> Originally-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
>>> Signed-off-by: Alex Shi <alexs@kernel.org>
>>> ---
>>>  mm/zpdesc.h   | 56 +++++++++++++++++++++++++++++++++++++++++++++++++++
>>>  mm/zsmalloc.c | 19 ++++++++---------
>>>  2 files changed, 66 insertions(+), 9 deletions(-)
>>>  create mode 100644 mm/zpdesc.h
>>
>> Hi Alex, thanks for your effort in pushing this forward!
>>
>>> diff --git a/mm/zpdesc.h b/mm/zpdesc.h
>>> new file mode 100644
>>> index 000000000000..a1ab5ebaa936
>>> --- /dev/null
>>> +++ b/mm/zpdesc.h
>>> @@ -0,0 +1,56 @@
>>> +/* SPDX-License-Identifier: GPL-2.0 */
>>> +/* zpdesc.h: zswap.zpool memory descriptor
>>> + *
>>> + * Written by Alex Shi <alexs@kernel.org>
>>> + *           Hyeonggon Yoo <42.hyeyoo@gmail.com>
>>> + */
>>> +#ifndef __MM_ZPDESC_H__
>>> +#define __MM_ZPDESC_H__
>>> +
>>> +/*
>>> + * struct zpdesc -     Memory descriptor for zpool memory, now is for zsmalloc
>>> + * @flags:             Page flags, PG_private: identifies the first component page
>>> + * @lru:               Indirected used by page migration
>>
>> maybe Indirected -> Indirectly?
> 
> Hi Yoo,
> 
> Thanks for comments! Yes Indirectly is better. I will update it in next version.
> 
>>
>>> + * @next:              Next zpdesc in a zspage in zsmalloc zpool
>>> + * @handle:            For huge zspage in zsmalloc zpool
>>> + * @zspage:            Pointer to zspage in zsmalloc
>>> + *
>>> + * This struct overlays struct page for now. Do not modify without a good
>>> + * understanding of the issues.
>>> + */
>>> +struct zpdesc {
>>> +       unsigned long flags;
>>> +       struct list_head lru;
>>> +       unsigned long _zp_pad_1;
>>
>> for understanding, I think it'd be better to replace _zp_pad_1 with movable ops,
>> because mops reuses this 'mapping' field.
> 
> Right, 'mops' looks a bit more clear.
> 
>>
>>> +       union {
>>> +               /* Next zpdescs in a zspage in zsmalloc zpool */
>>> +               struct zpdesc *next;
>>> +               /* For huge zspage in zsmalloc zpool */
>>> +               unsigned long handle;
>>> +       };
>>> +       struct zspage *zspage;
>>
>> There was a discussion with Yosry on including memcg_data on zpdesc
>> even if it's not used at the moment.
>>
>> Maybe you can look at:
>> https://lore.kernel.org/linux-mm/CAB=+i9Quz9iP2-Lq=oQfKVVnzPDtOaKMm=hUPbnRg5hRxH+qaA@mail.gmail.com/
> 
> Thanks for notice. 
> The memcg_data isn't used for zpdesc. And I have a bit confusion since Yosry said: "I think to drop memcg_data we need to enlighten the code that ...". So we actually don't need to have this unused member, is this right, Yosry?
> 
>>
>>> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
>>> index fec1a39e5bbe..67bb80b7413a 100644
>>> --- a/mm/zsmalloc.c
>>> +++ b/mm/zsmalloc.c
>>> @@ -13,17 +13,17 @@
>>>
>>>  /*
>>>   * Following is how we use various fields and flags of underlying
>>> - * struct page(s) to form a zspage.
>>> + * struct zpdesc(page) to form a zspage.
>>>   *
>>> - * Usage of struct page fields:
>>> - *     page->private: points to zspage
>>> - *     page->index: links together all component pages of a zspage
>>> + * Usage of struct zpdesc fields:
>>> + *     zpdesc->zspage: points to zspage
>>> + *     zpdesc->next: 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
>>>   *             offset in a subpage of a zspage
>>>   *
>>> - * Usage of struct page flags:
>>> + * Usage of struct zpdesc(page) flags:
>>>   *     PG_private: identifies the first component page
>>>   *     PG_owner_priv_1: identifies the huge component page
>>
>> the comment for PG_owner_priv_1 can safely be removed as it's not used
>> after commit a41ec880aa7b ("zsmalloc: move huge compressed obj from
>> page to zspage")
> 
> Right, thanks for info!
> 
>>
>>> @@ -948,7 +949,7 @@ static void create_page_chain(struct size_class *class, struct zspage *zspage,
>>>                 set_page_private(page, (unsigned long)zspage);
>>>                 page->index = 0;
>>>                 if (i == 0) {
>>> -                       zspage->first_page = page;
>>> +                       zspage->first_zpdesc = page_zpdesc(page);
>>>                         SetPagePrivate(page);
>>>                         if (unlikely(class->objs_per_zspage == 1 &&
>>>                                         class->pages_per_zspage == 1))
>>> @@ -1325,7 +1326,7 @@ static unsigned long obj_malloc(struct zs_pool *pool,
>>>                 link->handle = handle;
>>>         else
>>>                 /* record handle to page->index */
>>> -               zspage->first_page->index = handle;
>>> +               zspage->first_zpdesc->handle = handle;
>>
>> FYI this line seems to conflict with
>> bcc6116e39f512 ("mm/zsmalloc: move record_obj() into obj_malloc()")
>> on mm-unstable.
> 
> yes, a new commit made this conflict. will update this in next version.
> 
> Thanks
> Alex
>>
>> Best,
>> Hyeonggon

Re: [PATCH 01/20] mm/zsmalloc: add zpdesc memory descriptor for zswap.zpool

[Yosry Ahmed]

[..]
> >> +       union {
> >> +               /* Next zpdescs in a zspage in zsmalloc zpool */
> >> +               struct zpdesc *next;
> >> +               /* For huge zspage in zsmalloc zpool */
> >> +               unsigned long handle;
> >> +       };
> >> +       struct zspage *zspage;
> >
> > There was a discussion with Yosry on including memcg_data on zpdesc
> > even if it's not used at the moment.
> >
> > Maybe you can look at:
> > https://lore.kernel.org/linux-mm/CAB=+i9Quz9iP2-Lq=oQfKVVnzPDtOaKMm=hUPbnRg5hRxH+qaA@mail.gmail.com/
>
> Thanks for notice.
> The memcg_data isn't used for zpdesc. And I have a bit confusion since Yosry said: "I think to drop memcg_data we need to enlighten the code that ...". So we actually don't need to have this unused member, is this right, Yosry?

I think we need to have it, at least for now. When the pages are
freed, put_page() -> folio_put() -> __folio_put() will call
mem_cgroup_uncharge(). The latter will call folio_memcg() (which reads
folio->memcg_data) to figure out if uncharging needs to be done.

There are also other similar code paths that will check
folio->memcg_data. It is currently expected to be present for all
folios. So until we have custom code paths per-folio type for
allocation/freeing/etc, we need to keep folio->memcg_data present and
properly initialized.

Re: [PATCH 01/20] mm/zsmalloc: add zpdesc memory descriptor for zswap.zpool

[Alex Shi]

On 7/1/24 9:42 PM, Yosry Ahmed wrote:
> [..]
>>>> +       union {
>>>> +               /* Next zpdescs in a zspage in zsmalloc zpool */
>>>> +               struct zpdesc *next;
>>>> +               /* For huge zspage in zsmalloc zpool */
>>>> +               unsigned long handle;
>>>> +       };
>>>> +       struct zspage *zspage;
>>>
>>> There was a discussion with Yosry on including memcg_data on zpdesc
>>> even if it's not used at the moment.
>>>
>>> Maybe you can look at:
>>> https://lore.kernel.org/linux-mm/CAB=+i9Quz9iP2-Lq=oQfKVVnzPDtOaKMm=hUPbnRg5hRxH+qaA@mail.gmail.com/
>>
>> Thanks for notice.
>> The memcg_data isn't used for zpdesc. And I have a bit confusion since Yosry said: "I think to drop memcg_data we need to enlighten the code that ...". So we actually don't need to have this unused member, is this right, Yosry?
> 
> I think we need to have it, at least for now. When the pages are
> freed, put_page() -> folio_put() -> __folio_put() will call
> mem_cgroup_uncharge(). The latter will call folio_memcg() (which reads
> folio->memcg_data) to figure out if uncharging needs to be done.
> 
> There are also other similar code paths that will check
> folio->memcg_data. It is currently expected to be present for all
> folios. So until we have custom code paths per-folio type for
> allocation/freeing/etc, we need to keep folio->memcg_data present and
> properly initialized.

Hi Yosry,

Many thanks for detailed comments and requirements! 
I'm going to add this member in next version, maybe tomorrow, unless there are more comments for this patchset. :)

Thank a lot!
Alex