From: zhong jiang <[email protected]>
At present, zhdr->first_num plus bud can exceed the BUDDY_MASK
in encode_handle, it will lead to the the caller handle_to_buddy
return the error value.
The patch fix the issue by changing the BUDDY_MASK to PAGE_MASK,
it will be consistent with handle_to_z3fold_header. At the same time,
change the BUDDY_MASK to PAGE_MASK in handle_to_buddy is better.
Signed-off-by: zhong jiang <[email protected]>
---
mm/z3fold.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/mm/z3fold.c b/mm/z3fold.c
index 8f9e89c..e8fc216 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -169,7 +169,7 @@ static unsigned long encode_handle(struct z3fold_header *zhdr, enum buddy bud)
handle = (unsigned long)zhdr;
if (bud != HEADLESS)
- handle += (bud + zhdr->first_num) & BUDDY_MASK;
+ handle += (bud + zhdr->first_num) & PAGE_MASK;
return handle;
}
@@ -183,7 +183,7 @@ static struct z3fold_header *handle_to_z3fold_header(unsigned long handle)
static enum buddy handle_to_buddy(unsigned long handle)
{
struct z3fold_header *zhdr = handle_to_z3fold_header(handle);
- return (handle - zhdr->first_num) & BUDDY_MASK;
+ return (handle - zhdr->first_num) & PAGE_MASK;
}
/*
--
1.8.3.1
Hi, Vitaly
About the following patch, is it right?
Thanks
zhongjiang
On 2016/10/13 12:02, zhongjiang wrote:
> From: zhong jiang <[email protected]>
>
> At present, zhdr->first_num plus bud can exceed the BUDDY_MASK
> in encode_handle, it will lead to the the caller handle_to_buddy
> return the error value.
>
> The patch fix the issue by changing the BUDDY_MASK to PAGE_MASK,
> it will be consistent with handle_to_z3fold_header. At the same time,
> change the BUDDY_MASK to PAGE_MASK in handle_to_buddy is better.
>
> Signed-off-by: zhong jiang <[email protected]>
> ---
> mm/z3fold.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index 8f9e89c..e8fc216 100644
> --- a/mm/z3fold.c
> +++ b/mm/z3fold.c
> @@ -169,7 +169,7 @@ static unsigned long encode_handle(struct z3fold_header *zhdr, enum buddy bud)
>
> handle = (unsigned long)zhdr;
> if (bud != HEADLESS)
> - handle += (bud + zhdr->first_num) & BUDDY_MASK;
> + handle += (bud + zhdr->first_num) & PAGE_MASK;
> return handle;
> }
>
> @@ -183,7 +183,7 @@ static struct z3fold_header *handle_to_z3fold_header(unsigned long handle)
> static enum buddy handle_to_buddy(unsigned long handle)
> {
> struct z3fold_header *zhdr = handle_to_z3fold_header(handle);
> - return (handle - zhdr->first_num) & BUDDY_MASK;
> + return (handle - zhdr->first_num) & PAGE_MASK;
> }
>
> /*
Hi Zhong Jiang,
On Mon, Oct 17, 2016 at 3:58 AM, zhong jiang <[email protected]> wrote:
> Hi, Vitaly
>
> About the following patch, is it right?
>
> Thanks
> zhongjiang
> On 2016/10/13 12:02, zhongjiang wrote:
>> From: zhong jiang <[email protected]>
>>
>> At present, zhdr->first_num plus bud can exceed the BUDDY_MASK
>> in encode_handle, it will lead to the the caller handle_to_buddy
>> return the error value.
>>
>> The patch fix the issue by changing the BUDDY_MASK to PAGE_MASK,
>> it will be consistent with handle_to_z3fold_header. At the same time,
>> change the BUDDY_MASK to PAGE_MASK in handle_to_buddy is better.
are you seeing problems with the existing code? first_num should wrap around
BUDDY_MASK and this should be ok because it is way bigger than the number
of buddies.
~vitaly
On 2016/10/17 20:03, Vitaly Wool wrote:
> Hi Zhong Jiang,
>
> On Mon, Oct 17, 2016 at 3:58 AM, zhong jiang <[email protected]> wrote:
>> Hi, Vitaly
>>
>> About the following patch, is it right?
>>
>> Thanks
>> zhongjiang
>> On 2016/10/13 12:02, zhongjiang wrote:
>>> From: zhong jiang <[email protected]>
>>>
>>> At present, zhdr->first_num plus bud can exceed the BUDDY_MASK
>>> in encode_handle, it will lead to the the caller handle_to_buddy
>>> return the error value.
>>>
>>> The patch fix the issue by changing the BUDDY_MASK to PAGE_MASK,
>>> it will be consistent with handle_to_z3fold_header. At the same time,
>>> change the BUDDY_MASK to PAGE_MASK in handle_to_buddy is better.
> are you seeing problems with the existing code? first_num should wrap around
> BUDDY_MASK and this should be ok because it is way bigger than the number
> of buddies.
>
> ~vitaly
>
> .
>
first_num plus buddies can exceed the BUDDY_MASK. is it right?
(first_num + buddies) & BUDDY_MASK may be a smaller value than first_num.
but (handle - zhdr->first_num) & BUDDY_MASK will return incorrect value
in handle_to_buddy.
Thanks
zhongjiang
On 2016/10/17 20:03, Vitaly Wool wrote:
> Hi Zhong Jiang,
>
> On Mon, Oct 17, 2016 at 3:58 AM, zhong jiang <[email protected]> wrote:
>> Hi, Vitaly
>>
>> About the following patch, is it right?
>>
>> Thanks
>> zhongjiang
>> On 2016/10/13 12:02, zhongjiang wrote:
>>> From: zhong jiang <[email protected]>
>>>
>>> At present, zhdr->first_num plus bud can exceed the BUDDY_MASK
>>> in encode_handle, it will lead to the the caller handle_to_buddy
>>> return the error value.
>>>
>>> The patch fix the issue by changing the BUDDY_MASK to PAGE_MASK,
>>> it will be consistent with handle_to_z3fold_header. At the same time,
>>> change the BUDDY_MASK to PAGE_MASK in handle_to_buddy is better.
> are you seeing problems with the existing code? first_num should wrap around
> BUDDY_MASK and this should be ok because it is way bigger than the number
> of buddies.
>
> ~vitaly
>
> .
>
I am curious about the z3fold implement, Thus, I am reviewing the code.
Thanks
zhongjiang
On Mon, Oct 17, 2016 at 8:48 AM, zhong jiang <[email protected]> wrote:
>
> On 2016/10/17 20:03, Vitaly Wool wrote:
> > Hi Zhong Jiang,
> >
> > On Mon, Oct 17, 2016 at 3:58 AM, zhong jiang <[email protected]> wrote:
> >> Hi, Vitaly
> >>
> >> About the following patch, is it right?
> >>
> >> Thanks
> >> zhongjiang
> >> On 2016/10/13 12:02, zhongjiang wrote:
> >>> From: zhong jiang <[email protected]>
> >>>
> >>> At present, zhdr->first_num plus bud can exceed the BUDDY_MASK
> >>> in encode_handle, it will lead to the the caller handle_to_buddy
> >>> return the error value.
> >>>
> >>> The patch fix the issue by changing the BUDDY_MASK to PAGE_MASK,
> >>> it will be consistent with handle_to_z3fold_header. At the same time,
> >>> change the BUDDY_MASK to PAGE_MASK in handle_to_buddy is better.
> > are you seeing problems with the existing code? first_num should wrap around
> > BUDDY_MASK and this should be ok because it is way bigger than the number
> > of buddies.
> >
> > ~vitaly
> >
> > .
> >
> first_num plus buddies can exceed the BUDDY_MASK. is it right?
yes.
>
> (first_num + buddies) & BUDDY_MASK may be a smaller value than first_num.
yes, but that doesn't matter; the value stored in the handle is never
accessed directly.
>
> but (handle - zhdr->first_num) & BUDDY_MASK will return incorrect value
> in handle_to_buddy.
the subtraction and masking will result in the correct buddy number,
even if (handle & BUDDY_MASK) < zhdr->first_num.
However, I agree it's nonobvious, and tying the first_num size to
NCHUNKS_ORDER is confusing - the number of chunks is completely
unrelated to the number of buddies.
Possibly a better way to handle first_num is to limit it to the order
of enum buddy to the actual range of possible buddy indexes, which is
0x3, i.e.:
#define BUDDY_MASK (0x3)
and
unsigned short first_num:2;
with that and a small bit of explanation in the encode_handle or
handle_to_buddy comments, it should be clear how the first_num and
buddy numbering work, including that overflow/underflow are ok (due to
the masking)...
>
> Thanks
> zhongjiang
>
>
On 2016/10/17 23:30, Dan Streetman wrote:
> On Mon, Oct 17, 2016 at 8:48 AM, zhong jiang <[email protected]> wrote:
>> On 2016/10/17 20:03, Vitaly Wool wrote:
>>> Hi Zhong Jiang,
>>>
>>> On Mon, Oct 17, 2016 at 3:58 AM, zhong jiang <[email protected]> wrote:
>>>> Hi, Vitaly
>>>>
>>>> About the following patch, is it right?
>>>>
>>>> Thanks
>>>> zhongjiang
>>>> On 2016/10/13 12:02, zhongjiang wrote:
>>>>> From: zhong jiang <[email protected]>
>>>>>
>>>>> At present, zhdr->first_num plus bud can exceed the BUDDY_MASK
>>>>> in encode_handle, it will lead to the the caller handle_to_buddy
>>>>> return the error value.
>>>>>
>>>>> The patch fix the issue by changing the BUDDY_MASK to PAGE_MASK,
>>>>> it will be consistent with handle_to_z3fold_header. At the same time,
>>>>> change the BUDDY_MASK to PAGE_MASK in handle_to_buddy is better.
>>> are you seeing problems with the existing code? first_num should wrap around
>>> BUDDY_MASK and this should be ok because it is way bigger than the number
>>> of buddies.
>>>
>>> ~vitaly
>>>
>>> .
>>>
>> first_num plus buddies can exceed the BUDDY_MASK. is it right?
> yes.
>
>> (first_num + buddies) & BUDDY_MASK may be a smaller value than first_num.
> yes, but that doesn't matter; the value stored in the handle is never
> accessed directly.
>
>> but (handle - zhdr->first_num) & BUDDY_MASK will return incorrect value
>> in handle_to_buddy.
> the subtraction and masking will result in the correct buddy number,
> even if (handle & BUDDY_MASK) < zhdr->first_num.
yes, I see. it is hard to read.
> However, I agree it's nonobvious, and tying the first_num size to
> NCHUNKS_ORDER is confusing - the number of chunks is completely
> unrelated to the number of buddies.
yes. indeed.
> Possibly a better way to handle first_num is to limit it to the order
> of enum buddy to the actual range of possible buddy indexes, which is
> 0x3, i.e.:
>
> #define BUDDY_MASK (0x3)
>
> and
>
> unsigned short first_num:2;
>
> with that and a small bit of explanation in the encode_handle or
> handle_to_buddy comments, it should be clear how the first_num and
> buddy numbering work, including that overflow/underflow are ok (due to
> the masking)...
yes, It is better and clearer. Thanks for your relpy and advice. I will
resend the patch.
>> Thanks
>> zhongjiang
>>
>>
> .
>