linux-kernel - Re: [PATCH v2] mm/swapfile.c: simplify the scan loop in scan_swap_map

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Message-ID: <20200425003012.uuqh547feq3kz4y5@master>
Date:   Sat, 25 Apr 2020 00:30:12 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     Wei Yang <richard.weiyang@...il.com>, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH v2] mm/swapfile.c: simplify the scan loop in
 scan_swap_map_slots()

On Fri, Apr 24, 2020 at 10:02:58AM +0800, Huang, Ying wrote:
>Wei Yang <richard.weiyang@...il.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?

>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