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UPDATE:

It's a padding: every such non-rwx area is preceded with a readable and/or writable area and together they constitute a 64Mb segment (for 64bit architecture).

A relevant question on SO: https://stackoverflow.com/q/6568043/251311

I have discovered there are plenty of VM segments that don't have any of rwx flags, just p:

7f7e98033000-7f7e9c000000 ---p 00000000 00:00 0 Size: 65332 kB Rss: 0 kB Pss: 0 kB Shared_Clean: 0 kB Shared_Dirty: 0 kB Private_Clean: 0 kB Private_Dirty: 0 kB Referenced: 0 kB Anonymous: 0 kB AnonHugePages: 0 kB Swap: 0 kB KernelPageSize: 4 kB MMUPageSize: 4 kB

Any reference on what it means?

Unlike what's described in http://www.greenend.org.uk/rjk/tech/dataseg.html, it's not a mapping from a shared library since it does not have a corresponding fd attached. It's a custom long running C++ daemon, but I found some other processes have similar usage patterns: eg erlang (which also has plenty of them). In contrast long running php-fpm and python processes have literally 0 of such segments. "What other mappings does it have?" --- everything else is kind of expected and usual: just normal r/w private segments and shared libraries.

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  • @Gilles I've run through the links in your answer (especially the greenend.org.uk/rjk/tech/dataseg.html which is a gem), do you think it has the same nature as with shared libraries? Eg: it's done by a linker (or something else) to enforce placement of something separated from something else? My extremely limited understanding of memory management allows me understand why it can be helpful for a shared library case, but here it's an anonymous private page. Do you think it's the case here as well? Commented Oct 11, 2015 at 22:02
  • Hmm, true, there could be some other reason to have a private page with no permissions (none that comes to mind, but it's technically possible). But what makes you think that this isn't a mapping from a shared library? What process is it? What other mappings does it have? Commented Oct 11, 2015 at 22:12
  • It's not a mapping from a shared library since it does not have a corresponding fd attached. It's a custom long running C++ daemon, but I found some other processes have similar usage patterns: eg erlang (which also has plenty of them). In contrast long running php-fpm and python processes have literally 0 of such segments. "What other mappings does it have?" --- everything else is kind of expected and usual: just normal r/w private segments and shared libraries. Commented Oct 11, 2015 at 22:14
  • @Gilles seems like it's padding (relevant macro is HEAP_MAX_SIZE). Having that keyword I could find something relevant. And what is funny is that you have edited that question as well! :-D stackoverflow.com/q/6568043/251311 Commented Oct 13, 2015 at 20:45

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