madvise() vs posix_fadvise()

[Trond Endrestøl]

On Fri, 21 Mar 2014 18:56+0400, Dmitry Sivachenko wrote:

> Hello!
> 
> I have a program which uses large data files (read-only, via mmap()).
> 
> These machines have a bit more RAM that these files occupy, so it is 
> possible to have all these data in memory.
> 
> What techniques should I use to promote this data not to be purged 
> from RAM:
> 
> -- madvise(MADV_WILLNEED)
> -- posix_fadvise(POSIX_FADV_WILLNEED)
> -- both?

Although a bit dangerous, mlock(2) might be your ticket. That system 
call prevents your memory region from being swapped/paged away from 
physical memory.

> Some parts of this mmap()ed data is frequently accessed, some is 
> not, and I see that rarely accessed regions are purged from RAM.  I 
> want disk cache (program writes large log files) to have lower 
> priority, so disk cache does not purge mmaped regions from memory.
> 
> Thanks.

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