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From:   "Huang\, Ying" <ying.huang@intel.com>
To:     Daniel Jordan <daniel.m.jordan@oracle.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Michal Hocko <mhocko@suse.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Shaohua Li <shli@kernel.org>, Hugh Dickins <hughd@google.com>,
        Minchan Kim <minchan@kernel.org>,
        Rik van Riel <riel@redhat.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        Zi Yan <zi.yan@cs.rutgers.edu>
Subject: Re: [PATCH -mm -V3 03/21] mm, THP, swap: Support PMD swap mapping in swap_duplicate()
References: <20180523082625.6897-1-ying.huang@intel.com>
        <20180523082625.6897-4-ying.huang@intel.com>
        <20180611204231.ojhlyrbmda6pouxb@ca-dmjordan1.us.oracle.com>
        <87o9ggpzlk.fsf@yhuang-dev.intel.com>
Date:   Tue, 12 Jun 2018 11:15:28 +0800
In-Reply-To: <87o9ggpzlk.fsf@yhuang-dev.intel.com> (Ying Huang's message of
        "Tue, 12 Jun 2018 09:23:19 +0800")
Message-ID: <87k1r4puen.fsf@yhuang-dev.intel.com>
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"Huang, Ying" <ying.huang@intel.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