Re: [PATCH] pre7-1 semicolon & nicely readableB

Re: [PATCH] pre7-1 semicolon & nicely readableB

[Roel van der Goot]

Hi Rik,

I want to inform you that there is a subtle difference between
the following two loops:

(i)

   while ((mm->swap_cnt << 2 * (i + 1) < max_cnt)
                   && i++ < 10);

(ii)

   while ((mm->swap_cnt << 2 * (i + 1) < max_cnt)
                   && i < 10)
           i++;

Cheers,
Roel.


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Re: [PATCH] pre7-1 semicolon & nicely readableB

[Rik van Riel]

On Mon, 1 May 2000, Roel van der Goot wrote:

> I want to inform you that there is a subtle difference between
> the following two loops:
> 
> (i)
> 
>    while ((mm->swap_cnt << 2 * (i + 1) < max_cnt)
>                    && i++ < 10);
> 
> (ii)
> 
>    while ((mm->swap_cnt << 2 * (i + 1) < max_cnt)
>                    && i < 10)
>            i++;

I want to inform you that you're wrong. The only difference is
in readability.

If the first test fails, the clause behind the && won't be run.

Furthermore, i will only reach 10 if the RSS difference between
the current process and the biggest process is more than a factor
2^21 ... which can never happen on 32-bit hardware, unless the
RSS of the current process is 0.

In fact, the <10 test is only there to prevent infinite looping
for when a process with 0 swap_cnt "slips through" the tests above.

regards,

Rik
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Re: [PATCH] pre7-1 semicolon & nicely readable

[Roel van der Goot]

On Mon, 1 May 2000, Rik van Riel wrote:

> In fact, the <10 test is only there to prevent infinite looping
> for when a process with 0 swap_cnt "slips through" the tests above.

In case of a "slip through" variable i will have a different
value after the loop. But I understand from your reply that you
covered that case.

Cheers,
Roel.


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Re: [PATCH] pre7-1 semicolon & nicely readableB

[Chris Evans]

On Mon, 1 May 2000, Rik van Riel wrote:

> I want to inform you that you're wrong. The only difference is
> in readability.

[..]

> In fact, the <10 test is only there to prevent infinite looping
> for when a process with 0 swap_cnt "slips through" the tests above.

If such a value should never "slip through", then, for readability, you
want an assert (e.g. BUG() ).

Chris

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Re: [PATCH] pre7-1 semicolon & nicely readableB

[Rik van Riel]

On Tue, 2 May 2000, Chris Evans wrote:
> On Mon, 1 May 2000, Rik van Riel wrote:
> 
> > I want to inform you that you're wrong. The only difference is
> > in readability.
> 
> [..]
> 
> > In fact, the <10 test is only there to prevent infinite looping
> > for when a process with 0 swap_cnt "slips through" the tests above.
> 
> If such a value should never "slip through", then, for
> readability, you want an assert (e.g. BUG() ).

It's ok for them to slip through, it's just not ok for the kernel
to go into an infinite loop here...

Rik
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