[PATCH 01/15] mm/z3fold: add zpdesc struct and helper and use them in z3fold_page_isolate

[alexs@kernel.org]

From: Alex Shi <alexs@kernel.org>

The 1st patch here, we introduce some helper functions along with struct
zpdesc, like zpdesc_page/zpdesc_folio/page_zpdesc and zpdesc_address
similar with folio_address, and convert page to zpdesc in func
z3fold_page_isolate. z3fold_page_isolate() hooked to page_isolate that
the reason we could not fully remove page from its parameter for now.

Originally-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Alex Shi <alexs@kernel.org>
---
 mm/z3fold.c | 14 ++++++++------
 mm/zpdesc.h | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+), 6 deletions(-)
 create mode 100644 mm/zpdesc.h

diff --git a/mm/z3fold.c b/mm/z3fold.c
index 2ebfed32871b..b1229c0520f1 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -40,6 +40,7 @@
 #include <linux/spinlock.h>
 #include <linux/zpool.h>
 #include <linux/kmemleak.h>
+#include "zpdesc.h"
 
 /*
  * NCHUNKS_ORDER determines the internal allocation granularity, effectively
@@ -1251,22 +1252,23 @@ static bool z3fold_page_isolate(struct page *page, isolate_mode_t mode)
 {
 	struct z3fold_header *zhdr;
 	struct z3fold_pool *pool;
+	struct zpdesc *zpdesc = page_zpdesc(page);
 
-	VM_BUG_ON_PAGE(PageIsolated(page), page);
+	VM_BUG_ON_PAGE(PageIsolated(zpdesc_page(zpdesc)), zpdesc_page(zpdesc));
 
-	if (test_bit(PAGE_HEADLESS, &page->private))
+	if (test_bit(PAGE_HEADLESS, &zpdesc->zppage_flag))
 		return false;
 
-	zhdr = page_address(page);
+	zhdr = zpdesc_address(zpdesc);
 	z3fold_page_lock(zhdr);
-	if (test_bit(NEEDS_COMPACTING, &page->private) ||
-	    test_bit(PAGE_STALE, &page->private))
+	if (test_bit(NEEDS_COMPACTING, &zpdesc->zppage_flag) ||
+	    test_bit(PAGE_STALE, &zpdesc->zppage_flag))
 		goto out;
 
 	if (zhdr->mapped_count != 0 || zhdr->foreign_handles != 0)
 		goto out;
 
-	if (test_and_set_bit(PAGE_CLAIMED, &page->private))
+	if (test_and_set_bit(PAGE_CLAIMED, &zpdesc->zppage_flag))
 		goto out;
 	pool = zhdr_to_pool(zhdr);
 	spin_lock(&pool->lock);
diff --git a/mm/zpdesc.h b/mm/zpdesc.h
new file mode 100644
index 000000000000..d51785863596
--- /dev/null
+++ b/mm/zpdesc.h
@@ -0,0 +1,51 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* zpdesc.h: zswap.zpool memory descriptor
+ *
+ * Written by Alex Shi (Tencent) <alexs@kernel.org>
+ */
+#ifndef __MM_ZPDESC_H__
+#define __MM_ZPDESC_H__
+
+/*
+ * struct zpdesc -	Memory descriptor for z3fold memory
+ * @flags:		Page flags, PG_locked for headless z3fold memory
+ * @lru:		Indirected used by page migration
+ * @zppage_flag:	z3fold memory flags
+ *
+ * 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;
+	unsigned long _zp_pad_2;
+	unsigned long zppage_flag;
+};
+#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(private, zppage_flag);
+#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)))
+
+static inline void *zpdesc_address(const struct zpdesc *zpdesc)
+{
+	return folio_address(zpdesc_folio(zpdesc));
+}
+
+#endif
-- 
2.43.0