Re: Where in the code mmap + MAP_ANONYMOUS clears returned pages?

[Alexei Fedotov]

Thanks, Michal!
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Alexei Fedotov / ÐÐÐÐÑÐÐ ÐÐÐÐÑÐÐ,
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On Tue, Jul 15, 2014 at 11:14 PM, Michal Hocko <mhocko@xxxxxxx> wrote:
> On Tue 15-07-14 21:55:03, Alexei Fedotov wrote:
>> Guys,
>>
>> I look into mmap.c code [1] and try to understand where anonymous
>> memory mapping (mmap + MAP_ANONYMOUS) sets memory to zero. My best
>> guess is I should dig that somewhere in mmap_region.
>>
>> Could you please help me locating the code which makes returned memory
>> pages clean? Thank you in advance.
>
> mmap doesn't allocate pages which back the mapping directly unless it is
> told to by MAP_POPULATE. So the clean pages are either allocated during
> the page fault path when the memory is accessed (see do_anonymous_page
> for private 4k pages fault, do_huge_pmd_anonymous_page for THP page and
> MAP_SHARED is left as an excercise for the reader ;)) or in mmap path
> directly when MAP_POPULATE is specified (see vm_mmap_pgoff which calls
> mm_populate)
>
>>
>> [1] http://code.ohloh.net/file?fid=RPa2fuiQ5j_IwR1nymptYBBC3X4&cid=w6qrXNDsMqk
>>
>> --
>> With best regards / Ñ ÐÐÐÐÑÑÑÐÐÐ ÐÐÐÐÐÐÐÐÑÐÐ,
>> Alexei Fedotov / ÐÐÐÐÑÐÐ ÐÐÐÐÑÐÐ,
>> http://dataved.ru/
>> +7 916 562 8095
>>
>> [1] Start using Apache Openmeetings today, http://openmeetings.apache.org/
>> [2] Join Alexei Fedotov @linkedin, http://ru.linkedin.com/in/dataved/
>> [3] Join Alexei Fedotov @facebook, http://www.facebook.com/openmeetings
>> --
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>
> --
> Michal Hocko
> SUSE Labs
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