Re: [PATCH 3/3] mm/swapfile.c: count won't be bigger than SWAP_MAP_MAX

[Wei Yang]

On Sat, May 02, 2020 at 01:29:11PM +0000, Wei Yang wrote:
>On Fri, May 01, 2020 at 03:48:53PM -0700, Andrew Morton wrote:
>>On Fri,  1 May 2020 01:52:59 +0000 Wei Yang <richard.weiyang@xxxxxxxxx> wrote:
>>
>>> When the condition is true, there are two possibilities:
>>
>>I'm struggling with this one.
>>
>>>    1. count == SWAP_MAP_BAD
>>>    2. count == (SWAP_MAP_MAX & COUNT_CONTINUED) == SWAP_MAP_SHMEM
>>
>>I'm not sure what 2. is trying to say.  For a start, (SWAP_MAP_MAX &
>>COUNT_CONTINUED) is zero.  I guess it meant "|"?
>
>Oops, you are right. It should be (SWAP_MAP_MAX | COUNT_CONTINUED).
>
>Sorry for the confusion.
>

Hmm... I made a mistake again, the two cases should be

  * SWAP_MAP_BAD
  * (SWAP_MAP_BAD | COUNT_CONTINUED) == SWAP_MAP_SHMEM

What a shame.

>>
>>Also, the return value documentation says we return EINVAL for migration
>>entries.  Where's that happening, or is the comment out of date?
>>
>
>Not paid attention to this.
>
>Take look into the code, I don't find a relationship between the swap count
>and migration. Seems we just make a migration entry but not duplicate it.  
>If my understanding is correct.
>
>>> The first case would be filtered by the first if in __swap_duplicate().
>>> 
>>> And the second case means this swap entry is for shmem. Since we never
>>> do another duplication for shmem swap entry. This won't happen neither.
>>
>
>-- 
>Wei Yang
>Help you, Help me

-- 
Wei Yang
Help you, Help me