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AJvYcCXlDG+9QPg7t0PayIFJHwmlepmApgwjoy1qRolxLcW3OyfL+MpsLhHyXjt7rODSIj1WQjl2GHn7Og==@kvack.org X-Gm-Message-State: AOJu0Yxfw07yGu1KtRS51uR2VFkggTuqQeqnLvnlDV/vWbvhDHyE3SPn CQRDSNz872qTUMmrQXJqQf776dat+rMlClyhFyFV1wC9yBjTKDkSQeD5YGXBteLKrtvaDKD21Pz rpcLM5PsqMRGWMlnWENM86ostb5trRfrGV9fgm4GkdwByRna0uX/w X-Google-Smtp-Source: AGHT+IFN10uO7Gv80Xy38TQMAfn8kCvpzPHRJEbUH6QT906dpWAhof4RZ++pgvf6kg2EjLcNHqCBXsjfJjLE6WI+ato= X-Received: by 2002:a17:907:7d8d:b0:a99:497f:317 with SMTP id a640c23a62f3a-a999e8f7daemr151234466b.62.1728521219610; Wed, 09 Oct 2024 17:46:59 -0700 (PDT) MIME-Version: 1.0 References: <20241010003550.3695245-1-shakeel.butt@linux.dev> In-Reply-To: <20241010003550.3695245-1-shakeel.butt@linux.dev> From: Yosry Ahmed Date: Wed, 9 Oct 2024 17:46:22 -0700 Message-ID: Subject: Re: [PATCH] memcg: add tracing for memcg stat updates To: Shakeel Butt Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Steven Rostedt , JP Kobryn , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Stat-Signature: stebm1pyr87rjqtxmtij5pibjhd6zqix X-Rspamd-Queue-Id: DB3BE40002 X-Rspamd-Server: rspam11 X-HE-Tag: 1728521220-136836 X-HE-Meta: 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 4hOE6FXb lDBN0rJ0hfbG724zINhNNbEy6waTjF7vO/TNnfgrbpC17oGeLZXbcSqz9YwxGjCG2+TOngbswL17tr2kC+Rya5qQ+9tpEcCWCjA1yEda76B3+CUDjA4dpR6LrwB7alL63ZZCKqfKbutJzCW6Ce5epnAe3uBApEnYYmfHRpqAVEl60F0EX6fRK66AVIRQhGrQn/6G1 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 Wed, Oct 9, 2024 at 5:36=E2=80=AFPM Shakeel Butt wrote: > > The memcg stats are maintained in rstat infrastructure which provides > very fast updates side and reasonable read side. However memcg added > plethora of stats and made the read side, which is cgroup rstat flush, > very slow. To solve that, threshold was added in the memcg stats read > side i.e. no need to flush the stats if updates are within the > threshold. > > This threshold based improvement worked for sometime but more stats were > added to memcg and also the read codepath was getting triggered in the > performance sensitive paths which made threshold based ratelimiting > ineffective. We need more visibility into the hot and cold stats i.e. > stats with a lot of updates. Let's add trace to get that visibility. Good idea, thanks for doing this. > > Signed-off-by: Shakeel Butt > --- > include/trace/events/memcg.h | 59 ++++++++++++++++++++++++++++++++++++ > mm/memcontrol.c | 13 ++++++-- > 2 files changed, 70 insertions(+), 2 deletions(-) > create mode 100644 include/trace/events/memcg.h > > diff --git a/include/trace/events/memcg.h b/include/trace/events/memcg.h > new file mode 100644 > index 000000000000..913db9aba580 > --- /dev/null > +++ b/include/trace/events/memcg.h > @@ -0,0 +1,59 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +#undef TRACE_SYSTEM > +#define TRACE_SYSTEM memcg > + > +#if !defined(_TRACE_MEMCG_H) || defined(TRACE_HEADER_MULTI_READ) > +#define _TRACE_MEMCG_H > + > +#include > +#include > + > + > +DECLARE_EVENT_CLASS(memcg_rstat, > + > + TP_PROTO(struct mem_cgroup *memcg, int item, int val), > + > + TP_ARGS(memcg, item, val), > + > + TP_STRUCT__entry( > + __field(u64, id) > + __field(int, item) > + __field(int, val) > + ), > + > + TP_fast_assign( > + __entry->id =3D cgroup_id(memcg->css.cgroup); > + __entry->item =3D item; > + __entry->val =3D val; > + ), > + > + TP_printk("memcg_id=3D%llu item=3D%d val=3D%d", > + __entry->id, __entry->item, __entry->val) > +); > + > +DEFINE_EVENT(memcg_rstat, mod_memcg_state, > + > + TP_PROTO(struct mem_cgroup *memcg, int item, int val), > + > + TP_ARGS(memcg, item, val) > +); > + > +DEFINE_EVENT(memcg_rstat, mod_memcg_lruvec_state, > + > + TP_PROTO(struct mem_cgroup *memcg, int item, int val), > + > + TP_ARGS(memcg, item, val) > +); > + > +DEFINE_EVENT(memcg_rstat, count_memcg_events, > + > + TP_PROTO(struct mem_cgroup *memcg, int item, int val), > + > + TP_ARGS(memcg, item, val) > +); > + > + > +#endif /* _TRACE_MEMCG_H */ > + > +/* This part must be outside protection */ > +#include > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index c098fd7f5c5e..17af08367c68 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -71,6 +71,10 @@ > > #include > > +#define CREATE_TRACE_POINTS > +#include > +#undef CREATE_TRACE_POINTS > + > #include > > struct cgroup_subsys memory_cgrp_subsys __read_mostly; > @@ -682,7 +686,9 @@ void __mod_memcg_state(struct mem_cgroup *memcg, enum= memcg_stat_item idx, > return; > > __this_cpu_add(memcg->vmstats_percpu->state[i], val); > - memcg_rstat_updated(memcg, memcg_state_val_in_pages(idx, val)); > + val =3D memcg_state_val_in_pages(idx, val); > + memcg_rstat_updated(memcg, val); > + trace_mod_memcg_state(memcg, idx, val); Is it too unreasonable to include the stat name? The index has to be correlated with the kernel config and perhaps even version. It's not a big deal, but if performance is not a concern when tracing is enabled anyway, maybe we can lookup the name here (or in TP_fast_assign()). > } > > /* idx can be of type enum memcg_stat_item or node_stat_item. */ > @@ -741,7 +747,9 @@ static void __mod_memcg_lruvec_state(struct lruvec *l= ruvec, > /* Update lruvec */ > __this_cpu_add(pn->lruvec_stats_percpu->state[i], val); > > - memcg_rstat_updated(memcg, memcg_state_val_in_pages(idx, val)); > + val =3D memcg_state_val_in_pages(idx, val); > + memcg_rstat_updated(memcg, val); > + trace_mod_memcg_lruvec_state(memcg, idx, val); > memcg_stats_unlock(); > } > > @@ -832,6 +840,7 @@ void __count_memcg_events(struct mem_cgroup *memcg, e= num vm_event_item idx, > memcg_stats_lock(); > __this_cpu_add(memcg->vmstats_percpu->events[i], count); > memcg_rstat_updated(memcg, count); > + trace_count_memcg_events(memcg, idx, count); > memcg_stats_unlock(); > } > > -- > 2.43.5 >