From: zhong jiang <zhongjiang@xxxxxxxxxx>
At present, Tying the first_num size to NCHUNKS_ORDER is confusing.
the number of chunks is completely unrelated to the number of buddies.
The patch limit the first_num to actual range of possible buddy indexes.
and that is more reasonable and obvious without functional change.
Suggested-by: Dan Streetman <ddstreet@xxxxxxxx>
Signed-off-by: zhong jiang <zhongjiang@xxxxxxxxxx>
---
mm/z3fold.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/mm/z3fold.c b/mm/z3fold.c
index 8f9e89c..207e5dd 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -50,7 +50,7 @@
#define ZHDR_SIZE_ALIGNED CHUNK_SIZE
#define NCHUNKS ((PAGE_SIZE - ZHDR_SIZE_ALIGNED) >> CHUNK_SHIFT)
-#define BUDDY_MASK ((1 << NCHUNKS_ORDER) - 1)
+#define BUDDY_MASK (0x3)
struct z3fold_pool;
struct z3fold_ops {
@@ -109,7 +109,7 @@ struct z3fold_header {
unsigned short middle_chunks;
unsigned short last_chunks;
unsigned short start_middle;
- unsigned short first_num:NCHUNKS_ORDER;
+ unsigned short first_num:2;
};
/*
@@ -179,7 +179,11 @@ static struct z3fold_header *handle_to_z3fold_header(unsigned long handle)
return (struct z3fold_header *)(handle & PAGE_MASK);
}
-/* Returns buddy number */
+/*
+ * (handle & BUDDY_MASK) < zhdr->first_num is possible in encode_handle
+ * but that doesn't matter. because the masking will result in the
+ * correct buddy number.
+ */
static enum buddy handle_to_buddy(unsigned long handle)
{
struct z3fold_header *zhdr = handle_to_z3fold_header(handle);
--
1.8.3.1
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