Performance Degradation with rsync in container or cgroupv2 with MEM limit

[Alexandru Lazarev]

I'll answer my own question here:
Looks like it is a bug in Oracle Linux (OL) 9.2 RHCK Kernel
"kernel-5.14.0-284.11.1" (see table:
https://docs.oracle.com/en/operating-systems/oracle-linux/9/boot/oracle_linux9_kernel_version_matrix.html)

Switching to UEK Kernel of the same OL version (9.2) fixed the issue,
but UEK is not supported by some SW (e.g. Vertica DB), so that I've
tried RHCK Kernels update: only Kernel and dependencies from OL9.4
(kernel-5.14.0-427) and OL9.5 (kernel-5.14.0-503.11.1) - both fixed
the issue, with remark: RHCK update using one from OL9.5 is suspected
to have some HW compatibility issues (under investigation).
Some more details discussed here:
https://www.linuxquestions.org/questions/linux-containers-122/performance-degradation-with-rsync-in-container-or-cgroupv2-with-mem-limit-on-oracle-linux-9-2-rhck-5-14-vs-uek-5-15-a-4175749063/

On Wed, Mar 26, 2025 at 4:10 PM Alexandru Lazarev
<alexandru.lazarev at gmail.com> wrote:
>
> hi Greg,
> Thx for Your feedback - I would appreciate any feedback.
>
> I'am not paying for it - I am doing some tests on a given platform.
> Kernel is RHCK.
> I posted this question-issue here because maybe it is some generic
> kernel issue (I saw several of unanswered threads on various platforms
> of rsync degradation in containers) amnd someone can suggest to me
> right directions, OR..
> I know here in mail list are some people from Red Hat and Oracle which
> usually provide their valuable answered, so I am still keep my hopness
> on finding some ideas on this issue
>
> On Wed, Mar 26, 2025 at 4:00 PM Greg KH <greg at kroah.com> wrote:
> >
> > On Wed, Mar 26, 2025 at 02:11:41PM +0200, Alexandru Lazarev wrote:
> > > Hi everyone,
> > > I'm experiencing a significant performance degradation when using
> > > "rsync" to copy files over the network from within a container or
> > > cgroup with memory limits on Oracle Linux 9.2. The issue occurs with
> > > the Red Hat Compatible Kernel (RHCK) 5.14.0-284.11.1.el9_2.x86_64 but
> > > not with the Unbreakable Enterprise Kernel (UEK)
> > > 5.15.0-101.103.2.1.el9uek.x86_64.
> >
> > <snip>
> >
> > As you are paying for Oracle support for these kernels, please contact
> > them to take advantage of that support.  They are the only ones that can
> > help you out here as no one in the community has any idea of what is in
> > these kernels at all, sorry.
> >
> > good luck!
> >
> > greg k-h