Re: [PATCH -V2] swap: Reduce lock contention on swap cache from swap slots allocation

[Huang\, Ying]

Daniel Jordan <daniel.m.jordan@xxxxxxxxxx> writes:

> On Wed, May 20, 2020 at 11:15:02AM +0800, Huang Ying wrote:
>> @@ -2827,6 +2865,11 @@ static struct swap_info_struct *alloc_swap_info(void)
>>  	p = kvzalloc(struct_size(p, avail_lists, nr_node_ids), GFP_KERNEL);
>>  	if (!p)
>>  		return ERR_PTR(-ENOMEM);
>> +	p->cluster_next_cpu = alloc_percpu(unsigned int);
>> +	if (!p->cluster_next_cpu) {
>> +		kvfree(p);
>> +		return ERR_PTR(-ENOMEM);
>> +	}
>
> There should be free_percpu()s at two places after this, but I think the
> allocation really belongs right...
>
>> @@ -3202,7 +3245,10 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>>  		 * select a random position to start with to help wear leveling
>>  		 * SSD
>>  		 */
>> -		p->cluster_next = 1 + prandom_u32_max(p->highest_bit);
>
> ...here because then it's only allocated when it's actually used.

Good catch!  And yes, this is the better place to allocate memory.  I
will fix this in the new version!  Thanks a lot!

Best Regards,
Huang, Ying

>> +		for_each_possible_cpu(cpu) {
>> +			per_cpu(*p->cluster_next_cpu, cpu) =
>> +				1 + prandom_u32_max(p->highest_bit);
>> +		}
>>  		nr_cluster = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);
>>  
>>  		cluster_info = kvcalloc(nr_cluster, sizeof(*cluster_info),
>> -- 
>> 2.26.2
>> 
>>