After upgrading from 6.1 series kernel to 6.12.x series kernel, a
performance regression was encountered.

The customer is experiencing:

~2x slower execution times for write-heavy workloads under tight memory
cgroup limits (~256Mi)

Significant latency spikes (median 14s vs 7.1s on kernel 6.1; max 23.5s
vs 7.6s)

Occasional premature OOM conditions


Root Cause (Identified by Customer)

The issue is an upstream Linux kernel MGLRU regression:

Regression commit: 14aa8b2d5c2e ("mm/mglru: don't sync disk for each
aging cycle") – removed waking flusher threads during MGLRU reclaim,
causing dirty page accumulation and reclaim stalls under cgroup memory
pressure.

Fix commit: 1bc542c6a0d1 ("mm/vmscan: wake up flushers conditionally to
avoid cgroup OOM") – available in mainline ~6.13/6.14 but not backported
to the 6.12.x stable series (no Cc: stable tag). Ubuntu had to manually
SRU it.

Validation: Disabling MGLRU (/sys/kernel/mm/lru_gen/enabled=0) on kernel
6.12 nodes restores near-6.1 performance and eliminates the latency
tail, confirming the MGLRU reclaim path as the cause.


Please include the fix commit in the 6.12 series kernel.

Hi stable maintainers,

Brian Maly reported in Debian (bugreport
https://bugs.debian.org/1143545) when updating from the 6.1.y series
to the 6.12.y series and noticed it is caused by 6.12.y missing the
commit 1bc542c6a0d1 ("mm/vmscan: wake up flushers conditionally to
avoid cgroup OOM"):
flushers conditionally to avoid cgroup OOM") for 6.12.y?

Regards,
Salvatore

Queued for 6.12, thanks.