Please apply commit 1bc542c6a0d1 ("mm/vmscan: wake up flushers conditionally to avoid cgroup OOM") to v6.12.y

Control: forwarded -1 https://lore.kernel.org/stable/[email protected]

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"):

On Mon, Aug 03, 2026 at 09:52:09PM -0400, Brian Maly wrote:
> Package: kernel
> Version: 6.12.94-1
>
>
> 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.

Can you thus please backport/pick 1bc542c6a0d1 ("mm/vmscan: wake up
flushers conditionally to avoid cgroup OOM") for 6.12.y?

Regards,
Salvatore