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b=EyjAmEG1mTlciR+Q3Pcu6rKB451iaUX1ubjjD75vg2cCz5MHYoxTG9ISioIvBP9vu +9gtR0B7cdNs9zCQgLp7Dg/eonIRj075LWtGlj0+4VWRI+TJSoTN84IGAOVcYse93H IiLPbaaqQg3j76996tOqOQe/iow8c1mE6A3NZRap1GBsWlWeQxxtoj4JF1EPWoAk5s STZyiN6tQs/yhJ7cWa01+Hqi3xLTuakIZvDU1H+0xhxjSJZFhwhKtTQJo1nVg9azO5 s0CLYSZwBMS7kudRlamI8p64Q/01LBuLRit/MQrid92i7uLtL34SwTDFACJuOLMM4l vdzeOqkD8mquA== Message-ID: <6ee2518b-81dd-4082-bdf5-322883895ffc@kernel.org> Date: Fri, 7 Jun 2024 19:26:47 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 6.6.y] mm: ratelimit stat flush from workingset shrinker To: Shakeel Butt Cc: stable@vger.kernel.org, yosryahmed@google.com, tj@kernel.org, hannes@cmpxchg.org, lizefan.x@bytedance.com, cgroups@vger.kernel.org, longman@redhat.com, linux-mm@kvack.org, kernel-team@cloudflare.com References: <171776806121.384105.7980809581420394573.stgit@firesoul> Content-Language: en-US From: Jesper Dangaard Brouer In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 178A4140020 X-Stat-Signature: ewhjet4mqpz7idnwj8k6dyemdxbeimgg X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1717781214-154425 X-HE-Meta: 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 XLdMIXPu 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 07/06/2024 16.32, Shakeel Butt wrote: > On Fri, Jun 07, 2024 at 03:48:06PM GMT, Jesper Dangaard Brouer wrote: >> From: Shakeel Butt >> >> commit d4a5b369ad6d8aae552752ff438dddde653a72ec upstream. >> >> One of our workloads (Postgres 14 + sysbench OLTP) regressed on newer >> upstream kernel and on further investigation, it seems like the cause is >> the always synchronous rstat flush in the count_shadow_nodes() added by >> the commit f82e6bf9bb9b ("mm: memcg: use rstat for non-hierarchical >> stats"). On further inspection it seems like we don't really need >> accurate stats in this function as it was already approximating the amount >> of appropriate shadow entries to keep for maintaining the refault >> information. Since there is already 2 sec periodic rstat flush, we don't >> need exact stats here. Let's ratelimit the rstat flush in this code path. >> >> Link: https://lkml.kernel.org/r/20231228073055.4046430-1-shakeelb@google.com >> Fixes: f82e6bf9bb9b ("mm: memcg: use rstat for non-hierarchical stats") >> Signed-off-by: Shakeel Butt >> Cc: Johannes Weiner >> Cc: Yosry Ahmed >> Cc: Yu Zhao >> Cc: Michal Hocko >> Cc: Roman Gushchin >> Cc: Muchun Song >> Signed-off-by: Andrew Morton >> Signed-off-by: Jesper Dangaard Brouer >> >> --- >> On production with kernel v6.6 we are observing issues with excessive >> cgroup rstat flushing due to the extra call to mem_cgroup_flush_stats() >> in count_shadow_nodes() introduced in commit f82e6bf9bb9b ("mm: memcg: >> use rstat for non-hierarchical stats") that commit is part of v6.6. >> We request backport of commit d4a5b369ad6d ("mm: ratelimit stat flush >> from workingset shrinker") as it have a fixes tag for this commit. >> >> IMHO it is worth explaining call path that makes count_shadow_nodes() >> cause excessive cgroup rstat flushing calls. Function shrink_node() >> calls mem_cgroup_flush_stats() on its own first, and then invokes >> shrink_node_memcgs(). Function shrink_node_memcgs() iterates over >> cgroups via mem_cgroup_iter() for each calling shrink_slab(). The >> shrink_slab() calls do_shrink_slab() that via shrinker->count_objects() >> invoke count_shadow_nodes(), and count_shadow_nodes() does >> a mem_cgroup_flush_stats() call, that seems unnecessary. >> > > Actually at Meta production we have also replaced > mem_cgroup_flush_stats() in shrink_node() with > mem_cgroup_flush_stats_ratelimited() as it was causing too much flushing > issue. We have not observed any issue after the change. I will propose > that patch to upstream as well. (Please Cc me as I'm not subscribed on cgroups@vger.kernel.org) Yes, we also see mem_cgroup_flush_stats() in shrink_node() cause issues. So, I can confirm the issue. What we see is that it originates from kswapd, which have a kthread per NUMA node that runs concurrently... we measure cgroup rstat lock contention happening due to call in shrink_node(). See call stacks I captured with bpftrace script[1]: stack_wait[695, kswapd0, 1]: __cgroup_rstat_lock+107 __cgroup_rstat_lock+107 cgroup_rstat_flush_locked+851 cgroup_rstat_flush+35 shrink_node+226 balance_pgdat+807 kswapd+521 kthread+228 ret_from_fork+48 ret_from_fork_asm+27 @stack_wait[696, kswapd1, 1]: __cgroup_rstat_lock+107 __cgroup_rstat_lock+107 cgroup_rstat_flush_locked+851 cgroup_rstat_flush+35 shrink_node+226 balance_pgdat+807 kswapd+521 kthread+228 ret_from_fork+48 ret_from_fork_asm+27 @stack_wait[697, kswapd2, 1]: __cgroup_rstat_lock+107 __cgroup_rstat_lock+107 cgroup_rstat_flush_locked+851 cgroup_rstat_flush+35 shrink_node+226 balance_pgdat+807 kswapd+521 kthread+228 ret_from_fork+48 ret_from_fork_asm+27 @stack_wait[698, kswapd3, 1]: __cgroup_rstat_lock+107 __cgroup_rstat_lock+107 cgroup_rstat_flush_locked+851 cgroup_rstat_flush+35 shrink_node+226 balance_pgdat+807 kswapd+521 kthread+228 ret_from_fork+48 ret_from_fork_asm+27 @stack_wait[699, kswapd4, 1]: __cgroup_rstat_lock+107 __cgroup_rstat_lock+107 cgroup_rstat_flush_locked+851 cgroup_rstat_flush+35 shrink_node+226 balance_pgdat+807 kswapd+521 kthread+228 ret_from_fork+48 ret_from_fork_asm+27 @stack_wait[700, kswapd5, 1]: __cgroup_rstat_lock+107 __cgroup_rstat_lock+107 cgroup_rstat_flush_locked+851 cgroup_rstat_flush+35 shrink_node+226 balance_pgdat+807 kswapd+521 kthread+228 ret_from_fork+48 ret_from_fork_asm+27 @stack_wait[701, kswapd6, 1]: __cgroup_rstat_lock+107 __cgroup_rstat_lock+107 cgroup_rstat_flush_locked+851 cgroup_rstat_flush+35 shrink_node+226 balance_pgdat+807 kswapd+521 kthread+228 ret_from_fork+48 ret_from_fork_asm+27 @stack_wait[702, kswapd7, 1]: __cgroup_rstat_lock+107 __cgroup_rstat_lock+107 cgroup_rstat_flush_locked+851 cgroup_rstat_flush+35 shrink_node+226 balance_pgdat+807 kswapd+521 kthread+228 ret_from_fork+48 ret_from_fork_asm+27 --Jesper [1] https://github.com/xdp-project/xdp-project/blob/master/areas/latency/cgroup_rstat_latency.bt