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From: Wei Yang <richard.weiyang@gmail.com>
To: "Huang, Ying" <ying.huang@intel.com>
Cc: Wei Yang <richard.weiyang@gmail.com>,
	akpm@linux-foundation.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, Hugh Dickins <hughd@google.com>
Subject: Re: [PATCH v2] mm/swapfile.c: simplify the scan loop in scan_swap_map_slots()
Date: Sun, 26 Apr 2020 21:19:58 +0000	[thread overview]
Message-ID: <20200426211958.m7aheswirqaj2nte@master> (raw)
In-Reply-To: <87tv17xdfk.fsf@yhuang-dev.intel.com>

On Sun, Apr 26, 2020 at 09:07:11AM +0800, Huang, Ying wrote:
>Wei Yang <richard.weiyang@gmail.com> writes:
>
>> On Fri, Apr 24, 2020 at 10:02:58AM +0800, Huang, Ying wrote:
>>>Wei Yang <richard.weiyang@gmail.com> writes:
>>>
>> [...]
>>>>>
>>>>>if "offset > si->highest_bit" is true and "offset < scan_base" is true,
>>>>>scan_base need to be returned.
>>>>>
>>>>
>>>> When this case would happen in the original code?
>>>
>>>In the original code, the loop can still stop.
>>>
>>
>> Sorry, I don't get your point yet.
>>
>> In original code, there are two separate loops
>>
>>     while (++offset <= si->highest_bit) {
>>     }
>>
>>     while (offset < scan_base) {
>>     }
>>
>> And for your condition, (offset > highest_bit) && (offset < scan_base), which
>> terminates the first loop and fits the second loop well.
>>
>> Not sure how this condition would stop the loop in original code?
>
>Per my understanding, in your code, if some other task changes
>si->highest_bit to be less than scan_base in parallel.  The loop may
>cannot stop.

When (offset > scan_base), (offset >  si->highest_bit) means offset will be
set to si->lowest_bit.

When (offset < scan_base), next_offset() would always increase offset till
offset is scan_base.

Sorry, I didn't catch your case. Would you minding giving more detail?

>
>Best Regards,
>Huang, Ying
>
>>>Best Regards,
>>>Huang, Ying
>>>
>>>>>Again, the new code doesn't make it easier to find this kind of issues.
>>>>>
>>>>>Best Regards,
>>>>>Huang, Ying

-- 
Wei Yang
Help you, Help me


  reply	other threads:[~2020-04-26 21:20 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-22 21:41 Wei Yang
2020-04-23  5:57 ` Huang, Ying
2020-04-23 13:15   ` Wei Yang
2020-04-24  2:02     ` Huang, Ying
2020-04-25  0:30       ` Wei Yang
2020-04-26  1:07         ` Huang, Ying
2020-04-26 21:19           ` Wei Yang [this message]
2020-04-27  0:55             ` Huang, Ying
2020-04-28 21:22               ` Wei Yang
2020-04-29  0:52                 ` Huang, Ying
2020-04-29 22:06                   ` Wei Yang

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