mm/zsmalloc: don't need to reserve LSB in handle

We will save allocated tag in the object header to indicate that it's
allocated.

	handle |= OBJ_ALLOCATED_TAG;

So the object header needs to reserve LSB for this tag bit.

But the handle itself doesn't need to reserve LSB to save tag, since it's
only used to find the position of object, by (pfn + obj_idx).  So remove
LSB reserve from handle, one more bit can be used as obj_idx.

Link: https://lkml.kernel.org/r/20240228023854.3511239-1-chengming.zhou@linux.dev
Signed-off-by: Chengming Zhou <chengming.zhou@linux.dev>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 63ec385cd670f3e9c55ee24a6bc0a31f13a447de..7d7cb3eaabe029beaaf522c8521e8589cd0fafdd 100644 (file)
--- 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;
 }