Re: [PATCH -mm -v2] mm, swap: Sort swap entries before free

[Huang\, Ying]

Rik van Riel <riel@xxxxxxxxxx> writes:

> On Wed, 2017-04-05 at 15:10 +0800, Huang, Ying wrote:
>> To solve the issue, the per-CPU buffer is sorted according to the
>> swap
>> device before freeing the swap entries.ÂÂTest shows that the time
>> spent by swapcache_free_entries() could be reduced after the patch.
>
> That makes a lot of sense.
>
>> @@ -1075,6 +1083,8 @@ void swapcache_free_entries(swp_entry_t
>> *entries, int n)
>> Â
>> Â	prev = NULL;
>> Â	p = NULL;
>> +	if (nr_swapfiles > 1)
>> +		sort(entries, n, sizeof(entries[0]), swp_entry_cmp,
>> NULL);
>
> But it really wants a comment in the code, so people
> reading the code a few years from now can see why
> we are sorting things we are about to free.
>
> Maybe something like:
> Â Â Â Â /* Sort swap entries by swap device, so each lock is only taken
> once. */

Good suggestion!  I will add it in the next version.

Best Regards,
Huang, Ying

>> Â	for (i = 0; i < n; ++i) {
>> Â		p = swap_info_get_cont(entries[i], prev);
>> Â		if (p)