linux-kernel - [PATCH] mm/zsmalloc: don't need to save tag bit in handle

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Date: Tue, 27 Feb 2024 03:00:45 +0000
From: chengming.zhou@...ux.dev
To: minchan@...nel.org,
	senozhatsky@...omium.org,
	akpm@...ux-foundation.org
Cc: hannes@...xchg.org,
	nphamcs@...il.com,
	yosryahmed@...gle.com,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	chengming.zhou@...ux.dev,
	Chengming Zhou <zhouchengming@...edance.com>
Subject: [PATCH] mm/zsmalloc: don't need to save tag bit in handle

From: Chengming Zhou <zhouchengming@...edance.com>

We only need to save the position (pfn + obj_idx) in the handle, don't
need to save tag bit in handle. So one more bit can be used as obj_idx.

Actually, the tag bit is only useful in zspage's memory space, to tell
if an object is allocated or not.

Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
---
 mm/zsmalloc.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 63ec385cd670..7d7cb3eaabe0 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -110,7 +110,7 @@
 #define OBJ_TAG_BITS	1
 #define OBJ_TAG_MASK	OBJ_ALLOCATED_TAG
 
-#define OBJ_INDEX_BITS	(BITS_PER_LONG - _PFN_BITS - OBJ_TAG_BITS)
+#define OBJ_INDEX_BITS	(BITS_PER_LONG - _PFN_BITS)
 #define OBJ_INDEX_MASK	((_AC(1, UL) << OBJ_INDEX_BITS) - 1)
 
 #define HUGE_BITS	1
@@ -737,14 +737,12 @@ static struct page *get_next_page(struct page *page)
 static void obj_to_location(unsigned long obj, struct page **page,
 				unsigned int *obj_idx)
 {
-	obj >>= OBJ_TAG_BITS;
 	*page = pfn_to_page(obj >> OBJ_INDEX_BITS);
 	*obj_idx = (obj & OBJ_INDEX_MASK);
 }
 
 static void obj_to_page(unsigned long obj, struct page **page)
 {
-	obj >>= OBJ_TAG_BITS;
 	*page = pfn_to_page(obj >> OBJ_INDEX_BITS);
 }
 
@@ -759,7 +757,6 @@ static unsigned long location_to_obj(struct page *page, unsigned int obj_idx)
 
 	obj = page_to_pfn(page) << OBJ_INDEX_BITS;
 	obj |= obj_idx & OBJ_INDEX_MASK;
-	obj <<= OBJ_TAG_BITS;
 
 	return obj;
 }
-- 
2.40.1