linux-kernel - Re: [PATCH 3/6] swap: Unify normal/huge code path in swap_page_trans_huge

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Date:   Sat, 14 Jul 2018 20:53:12 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     Daniel Jordan <daniel.m.jordan@...cle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, Michal Hocko <mhocko@...e.com>,
        "Johannes Weiner" <hannes@...xchg.org>,
        Shaohua Li <shli@...nel.org>, Hugh Dickins <hughd@...gle.com>,
        Minchan Kim <minchan@...nel.org>,
        Rik van Riel <riel@...hat.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH 3/6] swap: Unify normal/huge code path in swap_page_trans_huge_swapped()

Daniel Jordan <daniel.m.jordan@...cle.com> writes:

> On Fri, Jul 13, 2018 at 07:36:33AM +0800, Huang, Ying wrote:
>> diff --git a/mm/swapfile.c b/mm/swapfile.c
>> index 75c84aa763a3..160f78072667 100644
>> --- a/mm/swapfile.c
>> +++ b/mm/swapfile.c
>> @@ -270,7 +270,10 @@ static inline void cluster_set_null(struct swap_cluster_info *info)
>>  
>>  static inline bool cluster_is_huge(struct swap_cluster_info *info)
>>  {
>> -	return info->flags & CLUSTER_FLAG_HUGE;
>> +	if (IS_ENABLED(CONFIG_THP_SWAP))
>> +		return info->flags & CLUSTER_FLAG_HUGE;
>> +	else
>> +		return false;
>>  }
>>  
>>  static inline void cluster_clear_huge(struct swap_cluster_info *info)
>> @@ -1489,9 +1492,6 @@ static bool swap_page_trans_huge_swapped(struct swap_info_struct *si,
>>  	int i;
>>  	bool ret = false;
>>  
>> -	if (!IS_ENABLED(CONFIG_THP_SWAP))
>> -		return swap_swapcount(si, entry) != 0;
>
> This tests the value returned from swap_count,
>
>> -
>>  	ci = lock_cluster_or_swap_info(si, offset);
>>  	if (!ci || !cluster_is_huge(ci)) {
>>  		if (map[roffset] != SWAP_HAS_CACHE)
>
> and now we're testing
>
>                     map[roffset] != SWAP_HAS_CACHE
>
> instead.  The two seem to mean the same thing here, since the swap slot hasn't
> been freed to the global pool and so can't be 0, but it might be better for
> consistency and clarity to use swap_count here, and a few lines down too
>
>         for (i = 0; i < SWAPFILE_CLUSTER; i++) {                                     
>                 if (map[offset + i] != SWAP_HAS_CACHE) {                             
>
> since swap_count seems to be used everywhere else for this.

Yes.  swap_count() looks better here.  Will change this.

Best Regards,
Huang, Ying