Potential future breakage on linux

[hoytech]

It looks like mincore() may be crippled in new linux kernels to protect against side-channel attacks: see this linux kernel commit

Unfortunately, on kernel versions 5.2+, you'll need to run vmtouch as root to get accurate page-residency information on files you don't have write access to.

[freedge]

indeed, we experienced issue with SLES12 and kernel 4.12.14-95.24 - vmtouch would just report every single file as fully present in the page cache.

It's a bit messy, Linus committed, then reverted, a patch for mincore. Not sure how newer kernel versions will behave.