mmap, msync and linux process termination

Question

I want to use mmap to implement persistence of certain portions of program state in a C program running under Linux by associating a fixed-size struct with a well known file name using mmap() with the MAP_SHARED flag set. For performance reasons, I would prefer not to call msync() at all, and no other programs will be accessing this file. When my program terminates and is restarted, it will map the same file again and do some processing on it to recover the state that it was in before the termination. My question is this: if I never call msync() on the file descriptor, will the kernel guarantee that all updates to the memory will get written to disk and be subsequently recoverable even if my process is terminated with SIGKILL? Also, will there be general system overhead from the kernel periodically writing the pages to disk even if my program never calls msync()?

EDIT: I've settled the problem of whether the data is written, but I'm still not sure about whether this will cause some unexpected system loading over trying to handle this problem with open()/write()/fsync() and taking the risk that some data might be lost if the process gets hit by KILL/SEGV/ABRT/etc. Added a 'linux-kernel' tag in hopes that some knowledgeable person might chime in.

Answer 1

I found a comment from Linus Torvalds that answers this question http://www.realworldtech.com/forum/?threadid=113923&curpostid=114068

The mapped pages are part of the filesystem cache, which means that even if the user process that made a change to that page dies, the page is still managed by the kernel and as all concurrent accesses to that file will go through the kernel, other processes will get served from that cache. In some old Linux kernels it was different, that's the reason why some kernel documents still tell to force msync.

EDIT: Thanks RobH corrected the link.

EDIT:

A new flag, MAP_SYNC, is introduced since Linux 4.15, which can guarantee the coherence.

Shared file mappings with this flag provide the guarantee that while some memory is writably mapped in the address space of the process, it will be visible in the same file at the same offset even after the system crashes or is rebooted.

references:

http://man7.org/linux/man-pages/man2/mmap.2.html search MAP_SYNC in the page

https://lwn.net/Articles/731706/