On Tue, Oct 18, 2016 at 3:57 PM, Dan Streetman <ddstreet@xxxxxxxx> wrote:
> 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>
Acked-by: Vitaly Wool <vitalywool@xxxxxxxxx>
>> ---> 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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