[Bug 2062556] Re: [Ubuntu-24.04] Hugepage memory is not getting released even after destroying the guest!

This bug is awaiting verification that the linux-
nvidia-6.8/6.8.0-1008.8~22.04.1 kernel in -proposed solves the problem.
Please test the kernel and update this bug with the results. If the
problem is solved, change the tag 'verification-needed-jammy-linux-
nvidia-6.8' to 'verification-done-jammy-linux-nvidia-6.8'. If the
problem still exists, change the tag 'verification-needed-jammy-linux-
nvidia-6.8' to 'verification-failed-jammy-linux-nvidia-6.8'.


If verification is not done by 5 working days from today, this fix will
be dropped from the source code, and this bug will be closed.


See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how
to enable and use -proposed. Thank you!


** Tags added: kernel-spammed-jammy-linux-nvidia-6.8-v2 verification-needed-jammy-linux-nvidia-6.8

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https://bugs.launchpad.net/bugs/2062556

Title:
[Ubuntu-24.04] Hugepage memory is not getting released even after
destroying the guest!

Status in The Ubuntu-power-systems project:
Fix Released
Status in linux package in Ubuntu:
Fix Released
Status in linux source package in Noble:
Fix Released

Bug description:
---Problem Description---

Hugepages memory is not getting released even after destroying the guest

Machine Type = P10 Denali LPAR

---uname output---
Linux ubuntu2404lp3 6.8.0-22-generic #22-Ubuntu SMP Thu Apr 4 22:47:57 UTC 2024 ppc64le ppc64le ppc64le GNU/Linux


---Steps to Reproduce---
1. Create a guest which is backed by hugepages.
2. Destroy the guest
3. execute "free -h" or "cat /proc/meminfo" to see that Hugepage memory is still getting held.


HugePages_Total: 20480
HugePages_Free: 20419
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 2048 kB
Hugetlb: 41943040 kB
DirectMap4k: 0 kB
DirectMap64k: 52428800 kB
DirectMap2M: 0 kB
DirectMap1G: 0 kB
root@ubuntu2404lp3:~# virsh list --all
Id Name State
---------------------------
- ramlp2g1 shut off
- ramlp2g2 shut off
- ramlp2g3 shut off
- ramlp3g3 shut off

root@ubuntu2404lp3:~# free -h
total used free shared buff/cache available
Mem: 48Gi 43Gi 4.6Gi 2.6Mi 277Mi 4.6Gi
Swap: 8.0Gi 243Mi 7.8Gi
root@ubuntu2404lp3:~#

====
This is an issue created by commit 1b151e2435fc ("block: Remove special-casing of compound pages") that moved the direct-io hugetlb handling from compound pages to folios.

Following commit has been proposed and merged into 6.9-rc1 which fixes this issue.
38b43539d64b2fa020b3b9a752a986769f87f7a6("block: Fix page refcounts for unaligned buffers in __bio_release_pages()")

So the same needs to be backported to the Ubuntu24.04 kernel as well.

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