Re: [PATCH 4/4] mm/gup: remove get_user_pages_locked()

[John Hubbard <jhubbard@nvidia.com>]

On 1/31/22 05:36, Jason Gunthorpe wrote:
...
>> @@ -968,15 +966,15 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask,
>>   	if (flags & MPOL_F_NODE) {
>>   		if (flags & MPOL_F_ADDR) {
>>   			/*
>> -			 * Take a refcount on the mpol, lookup_node()
>> -			 * will drop the mmap_lock, so after calling
>> -			 * lookup_node() only "pol" remains valid, "vma"
>> -			 * is stale.
>> +			 * Take a refcount on the mpol, because we are about to
>> +			 * drop the mmap_lock, after which only "pol" remains
>> +			 * valid, "vma" is stale.
>>   			 */
>>   			pol_refcount = pol;
>>   			vma = NULL;
>>   			mpol_get(pol);
>>   			err = lookup_node(mm, addr);
>> +			mmap_read_unlock(mm);
> 
> How about move the mmap_read_unlock up one line and then use
> get_user_pages_fast()
> 
> I'm guessing in most cases here the PTE will be present so that should
> be a net win?

Neat, I'll do that.


thanks,
-- 
John Hubbard
NVIDIA