linux-kernel - Re: [PATCH -next 1/2] PM: hibernate: fix spelling mistake for annotation

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Date:   Fri, 4 Nov 2022 15:31:49 +0800
From:   TGSP <tgsp002@...il.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     xiongxin@...inos.cn, len.brown@...el.com, pavel@....cz,
        huanglei@...inos.cn, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH -next 1/2] PM: hibernate: fix spelling mistake for
 annotation

在 2022/11/4 00:25, Rafael J. Wysocki 写道:
> On Tue, Nov 1, 2022 at 3:28 AM TGSP <tgsp002@...il.com> wrote:
>>
>> From: xiongxin <xiongxin@...inos.cn>
>>
>> The actual calculation formula in the code below is:
>>
>> max_size = (count - (size + PAGES_FOR_IO)) / 2
>>              - 2 * DIV_ROUND_UP(reserved_size, PAGE_SIZE);
>>
>> But function comments are written differently, the comment is wrong?
> 
> It is, and it is more serious than just a spelling mistake.
> 
>> By the way, what exactly do the "/ 2" and "2 *" mean?
> 
> Every page in the image is a copy of an existing allocated page, so
> room needs to be made for the two, except for the "IO pages" and
> metadata pages that are not copied.  Hence, the division by 2.
> 
> Now, the "reserved_size" pages will be allocated right before creating
> the image and there will be a copy of each of them in the image, so
> there needs to be room for twice as many.

According to your interpretation, the formula should be：
max_size = (count - 2 * DIV_ROUND_UP(reserved_size, PAGE_SIZE)
                - (size + PAGES_FOR_IO)) / 2

Am I right?

> 
> I'll adjust the changelog and queue up the path for 6.2.
> 
>> Cc: stable@...r.kernel.org
> 
> I'll add a Fixes tag instead.
> 
>> Signed-off-by: xiongxin <xiongxin@...inos.cn>
>> ---
>>   kernel/power/snapshot.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
>> index 2a406753af90..c20ca5fb9adc 100644
>> --- a/kernel/power/snapshot.c
>> +++ b/kernel/power/snapshot.c
>> @@ -1723,8 +1723,8 @@ static unsigned long minimum_image_size(unsigned long saveable)
>>    * /sys/power/reserved_size, respectively).  To make this happen, we compute the
>>    * total number of available page frames and allocate at least
>>    *
>> - * ([page frames total] + PAGES_FOR_IO + [metadata pages]) / 2
>> - *  + 2 * DIV_ROUND_UP(reserved_size, PAGE_SIZE)
>> + * ([page frames total] - PAGES_FOR_IO - [metadata pages]) / 2
>> + *  - 2 * DIV_ROUND_UP(reserved_size, PAGE_SIZE)
>>    *
>>    * of them, which corresponds to the maximum size of a hibernation image.
>>    *
>> --
>> 2.25.1
>>