Possible typo in madvise(2)

Possible typo in madvise(2)

[Alex Roper]

Version: Current git repo

The first paragraph of DESCRIPTION states that madvise does not change
the semantics of an application except in the case of MADV_DONTNEED,
which I believe should read MADV_DONTFORK.

Thanks,
Alex
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Re: Possible typo in madvise(2)

[Michael Kerrisk (man-pages)]

On 03/28/2014 12:16 AM, Alex Roper wrote:
> Version: Current git repo
> 
> The first paragraph of DESCRIPTION states that madvise does not change
> the semantics of an application except in the case of MADV_DONTNEED,
> which I believe should read MADV_DONTFORK.

Alex, 

MADV_DONTNEED does change the semantics. But, could you say more
about wht you think MADV_DONTFORK should have been written here 
instead? (Perhaps some fix is needed to the page.)

Thanks,

Michael

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Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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Re: Possible typo in madvise(2)

[Alex Roper]

Sorry for my confusion.

Checking other sources I see MADV_DONTNEED results in modifications to
private mappings being lost (the section on zero-filling non-file-backed
pages address this, in retrospect) which clearly changes semantics.

I had noticed that MADV_DONTFORK can result in different behavior after
a fork (eg, a parent mmaps a file, madvises dontfork, then forks, and
the child writes to the page -- with madvise, the page is updated,
visible to both processes, as is the backing file, without it the child
will segfault) and thought there might be a simple typo.

Alex

On 04/01/2014 02:18 PM, Michael Kerrisk (man-pages) wrote:
> On 03/28/2014 12:16 AM, Alex Roper wrote:
>> Version: Current git repo
>>
>> The first paragraph of DESCRIPTION states that madvise does not change
>> the semantics of an application except in the case of MADV_DONTNEED,
>> which I believe should read MADV_DONTFORK.
> 
> Alex, 
> 
> MADV_DONTNEED does change the semantics. But, could you say more
> about wht you think MADV_DONTFORK should have been written here 
> instead? (Perhaps some fix is needed to the page.)
> 
> Thanks,
> 
> Michael
> 
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Re: Possible typo in madvise(2)

[Alex Roper]

> I had noticed that MADV_DONTFORK can result in different behavior after
> a fork (eg, a parent mmaps a file, madvises dontfork, then forks, and
> the child writes to the page -- with madvise, the page is updated,
> visible to both processes, as is the backing file, without it the child
> will segfault) and thought there might be a simple typo.
Typo: I flipped with and without madvise cases here.
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