[PATCH] z3fold: limit first_num to the actual range of possible buddy indexes

[PATCH] z3fold: limit first_num to the actual range of possible buddy indexes

[zhongjiang]

From: zhong jiang <zhongjiang@huawei.com>

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@ieee.org>
Signed-off-by: zhong jiang <zhongjiang@huawei.com>
---
 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

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

Re: [PATCH] z3fold: limit first_num to the actual range of possible buddy indexes

[Dan Streetman]

On Tue, Oct 18, 2016 at 3:42 AM, zhongjiang <zhongjiang@huawei.com> wrote:
> From: zhong jiang <zhongjiang@huawei.com>
>
> 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@ieee.org>
> Signed-off-by: zhong jiang <zhongjiang@huawei.com>

Acked-by: Dan Streetman <ddstreet@ieee.org>

> --->  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
>

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

Re: [PATCH] z3fold: limit first_num to the actual range of possible buddy indexes

[Vitaly Wool]

On Tue, Oct 18, 2016 at 3:57 PM, Dan Streetman <ddstreet@ieee.org> wrote:
> On Tue, Oct 18, 2016 at 3:42 AM, zhongjiang <zhongjiang@huawei.com> wrote:
>> From: zhong jiang <zhongjiang@huawei.com>
>>
>> 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@ieee.org>
>> Signed-off-by: zhong jiang <zhongjiang@huawei.com>
>
> Acked-by: Dan Streetman <ddstreet@ieee.org>

Acked-by: Vitaly Wool <vitalywool@gmail.com>

>> --->  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
>>

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>