linux-kernel - Re: [PATCH -mm -V3 03/21] mm, THP, swap: Support PMD swap mapping in swap

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Message-ID: <87k1r4puen.fsf@yhuang-dev.intel.com>
Date:   Tue, 12 Jun 2018 11:15:28 +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>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        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>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Zi Yan <zi.yan@...rutgers.edu>
Subject: Re: [PATCH -mm -V3 03/21] mm, THP, swap: Support PMD swap mapping in swap_duplicate()

"Huang, Ying" <ying.huang@...el.com> 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