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charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.54.1 (3.54.1-1.fc41) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Sender: riel@surriel.com On Wed, 2025-01-29 at 01:06 +0800, Qi Zheng wrote: >=20 > I did reproduce the performance regression using the following test > program: >=20 > stress-ng --timeout 60 --times --verify --metrics --no-rand-seed=20 > --mmapaddr 64 >=20 > And its call stack is as follows: >=20 > bpftrace -e 'k:_raw_spin_unlock_irqrestore {@[kstack,comm]=3Dcount();}= =20 > interval:s:1 {exit();}' >=20 > @[ > _raw_spin_unlock_irqrestore+5 > free_one_page+85 > rcu_do_batch+424 > rcu_core+401 > handle_softirqs+204 > irq_exit_rcu+208 That looks like the RCU freeing somehow bypassing the per-cpu-pages, and hitting the zone->lock at page free time, while regular freeing usually puts pages in the CPU-local free page cache, without the lock? I'm not quite sure why this would be happening, though. Maybe the RCU batches are too big for the PCPs to hold them? If that is the case, chances are more code paths are hitting that issue, and we should just fix it, rather than trying to bypass it. Maybe the reason is more simple than that? I have not found a place where it explicitly bypasses the PCPs, but who knows? --=20 All Rights Reversed.