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SubjectRe: [PATCH] mm: memcontrol: use per-cpu stocks for socket memory uncharging
On Tue, Aug 29, 2017 at 03:26:21PM -0400, Johannes Weiner wrote:
> On Tue, Aug 29, 2017 at 11:01:50AM +0100, Roman Gushchin wrote:
> > We've noticed a quite sensible performance overhead on some hosts
> > with significant network traffic when socket memory accounting
> > is enabled.
> >
> > Perf top shows that socket memory uncharging path is hot:
> > 2.13% [kernel] [k] page_counter_cancel
> > 1.14% [kernel] [k] __sk_mem_reduce_allocated
> > 1.14% [kernel] [k] _raw_spin_lock
> > 0.87% [kernel] [k] _raw_spin_lock_irqsave
> > 0.84% [kernel] [k] tcp_ack
> > 0.84% [kernel] [k] ixgbe_poll
> > 0.83% < workload >
> > 0.82% [kernel] [k] enqueue_entity
> > 0.68% [kernel] [k] __fget
> > 0.68% [kernel] [k] tcp_delack_timer_handler
> > 0.67% [kernel] [k] __schedule
> > 0.60% < workload >
> > 0.59% [kernel] [k] __inet6_lookup_established
> > 0.55% [kernel] [k] __switch_to
> > 0.55% [kernel] [k] menu_select
> > 0.54% libc-2.20.so [.] __memcpy_avx_unaligned
> >
> > To address this issue, the existing per-cpu stock infrastructure
> > can be used.
> >
> > refill_stock() can be called from mem_cgroup_uncharge_skmem()
> > to move charge to a per-cpu stock instead of calling atomic
> > page_counter_uncharge().
> >
> > To prevent the uncontrolled growth of per-cpu stocks,
> > refill_stock() will explicitly drain the cached charge,
> > if the cached value exceeds CHARGE_BATCH.
> >
> > This allows significantly optimize the load:
> > 1.21% [kernel] [k] _raw_spin_lock
> > 1.01% [kernel] [k] ixgbe_poll
> > 0.92% [kernel] [k] _raw_spin_lock_irqsave
> > 0.90% [kernel] [k] enqueue_entity
> > 0.86% [kernel] [k] tcp_ack
> > 0.85% < workload >
> > 0.74% perf-11120.map [.] 0x000000000061bf24
> > 0.73% [kernel] [k] __schedule
> > 0.67% [kernel] [k] __fget
> > 0.63% [kernel] [k] __inet6_lookup_established
> > 0.62% [kernel] [k] menu_select
> > 0.59% < workload >
> > 0.59% [kernel] [k] __switch_to
> > 0.57% libc-2.20.so [.] __memcpy_avx_unaligned
> >
> > Signed-off-by: Roman Gushchin <guro@fb.com>
> > Cc: Johannes Weiner <hannes@cmpxchg.org>
> > Cc: Michal Hocko <mhocko@kernel.org>
> > Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
> > Cc: cgroups@vger.kernel.org
> > Cc: kernel-team@fb.com
> > Cc: linux-mm@kvack.org
> > Cc: linux-kernel@vger.kernel.org
>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
>
> Neat!
>
> As far as other types of pages go: page cache and anon are already
> batched pretty well, but I think kmem might benefit from this
> too. Have you considered using the stock in memcg_kmem_uncharge()?

Good idea!
I'll try to find an appropriate testcase and check if it really
brings any benefits. If so, I'll master a patch.

Thanks!

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