Pre-Content fanotify / fanotify Hierarchical Storage Management Expected For Linux 6.14

Queued up by way of linux-fs.git's "for_next" Git branch is the fanotify HSM (Hierarchical Storage Management) implementation via the pre-content fanotify patch series.

This code has been worked on by Meta engineers for a while and already the code is used in production in Meta for fanotify-based Hierarchical Storage Management / Tiered Storage handling using the fanotify API. The fanotify API is used for notification and interception of file-system events.

Being worked on for several months has been the pre-content hooks for fanotify worked on by Amir Goldstein and Josef Bacik. Bacik explained there:

"I did a bunch of testing, I also got some performance numbers. I copied a kernel tree, and then did remote-fetch, and then make -j4

Normal
real 9m49.709s
user 28m11.372s
sys 4m57.304s

HSM
real 10m6.454s
user 29m10.517s
sys 5m2.617s

So ~17 seconds more to build with HSM. I then did a make mrproper on both trees to see the size

[root@fedora ~]# du -hs /src/linux
1.6G /src/linux
[root@fedora ~]# du -hs dst
125M dst

This mirrors the sort of savings we've seen in production.

Meta has had these patches (minus the page fault patch) deployed in production for almost a year with our own utility for doing on-demand package fetching. The savings from this has been pretty significant.

The page-fault hooks are necessary for the last thing we need, which is on-demand range fetching of executables. Some of our binaries are several gigs large, having the ability to remote fetch them on demand is a huge win for us not only with space savings, but with startup time of containers."

The patches are queued up via this merge to linux-fs.git for_next, so barring any last minute issues they should end up being merged for Linux 6.14 in the new year.