Re: [PATCH -mm -V3 03/21] mm, THP, swap: Support PMD swap mapping in swap_duplicate()

[Huang\, Ying]

"Huang, Ying" <ying.huang@xxxxxxxxx> writes:
>> On Wed, May 23, 2018 at 04:26:07PM +0800, Huang, Ying wrote:
>>> @@ -3516,11 +3512,39 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
>>
>> Two comments about this part of __swap_duplicate as long as you're moving it to
>> another function:
>>
>>    } else if (count || has_cache) {
>>    
>>    	if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)          /* #1   */
>>    		count += usage;
>>    	else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)     /* #2   */
>>    		err = -EINVAL;
>>
>> #1:  __swap_duplicate_locked might use
>>
>>     VM_BUG_ON(usage != SWAP_HAS_CACHE && usage != 1);
>>
>> to document the unstated assumption that usage is 1 (otherwise count could
>> overflow).
>
> Sounds good.  Will do this.

Found usage parameter of __swap_duplicate() could be SWAP_MAP_SHMEM too.
We can improve the parameter checking.  But that appears not belong to
this series.

Best Regards,
Huang, Ying