On Tue, Oct 18, 2016 at 3:42 AM, zhongjiang <zhongjiang@xxxxxxxxxx> wrote:
> 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>
Acked-by: Dan Streetman <ddstreet@xxxxxxxx>
> ---> 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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