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From: Muchun Song In-Reply-To: <20250417144835.GE780688@cmpxchg.org> Date: Fri, 18 Apr 2025 10:38:10 +0800 Cc: Muchun Song , mhocko@kernel.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, akpm@linux-foundation.org, david@fromorbit.com, zhengqi.arch@bytedance.com, yosry.ahmed@linux.dev, nphamcs@gmail.com, chengming.zhou@linux.dev, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, hamzamahfooz@linux.microsoft.com, apais@linux.microsoft.com Content-Transfer-Encoding: quoted-printable Message-Id: References: <20250415024532.26632-1-songmuchun@bytedance.com> <20250415024532.26632-3-songmuchun@bytedance.com> <20250417144835.GE780688@cmpxchg.org> To: Johannes Weiner X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 9959C40006 X-Stat-Signature: muqp5peo7q44i9ne5erjupmsqt6r5cm4 X-Rspam-User: X-HE-Tag: 1744943937-895097 X-HE-Meta: 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 eY+enf7h kggTuhK8DKA/0a/nVR6uQEwFh0cOhLmznXP1hhZHRXuU0lq8zL6Nq6SNWwoXz5Yqf57n2FkKAhEJJtUlH9dSEkPKNElkEvXnQQpL7ojfCstRJmLHY+RgiHXcoPaAKwyW1Eq9PEi48xBXHn4FKvCLY9pI7tPjNhETMF/yOiNw3ePGwQ7eXoVnd5rJ+78Zg4ndCczqOc2VcVnXtwO+OceOaUhmxV674OCl09cj4R3GJMlzah3GN3C7JvArb0Zx/PTFahM94MKbpdhwGGfE8dxLmuMTrByecfNzTNV/1R1sNfim40zZfvMEYqCCQrKX4fxcejItya4JHLK7dmmngK/2fcPUi4g== 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 Apr 17, 2025, at 22:48, Johannes Weiner wrote: >=20 > On Tue, Apr 15, 2025 at 10:45:06AM +0800, Muchun Song wrote: >> If a folio isn't charged to the memory cgroup, holding an rcu read = lock >> is needless. Users only want to know its charge status, so use >> folio_memcg_charged() here. >>=20 >> Signed-off-by: Muchun Song >> --- >> mm/memcontrol.c | 11 ++++------- >> 1 file changed, 4 insertions(+), 7 deletions(-) >>=20 >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index 61488e45cab2..0fc76d50bc23 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -797,20 +797,17 @@ void __mod_lruvec_state(struct lruvec *lruvec, = enum node_stat_item idx, >> void __lruvec_stat_mod_folio(struct folio *folio, enum node_stat_item = idx, >> int val) >> { >> - struct mem_cgroup *memcg; >> pg_data_t *pgdat =3D folio_pgdat(folio); >> struct lruvec *lruvec; >>=20 >> - rcu_read_lock(); >> - memcg =3D folio_memcg(folio); >> - /* Untracked pages have no memcg, no lruvec. Update only the = node */ >> - if (!memcg) { >> - rcu_read_unlock(); >> + if (!folio_memcg_charged(folio)) { >> + /* Untracked pages have no memcg, no lruvec. Update only = the node */ >> __mod_node_page_state(pgdat, idx, val); >> return; >> } >>=20 >> - lruvec =3D mem_cgroup_lruvec(memcg, pgdat); >> + rcu_read_lock(); >> + lruvec =3D mem_cgroup_lruvec(folio_memcg(folio), pgdat); >> __mod_lruvec_state(lruvec, idx, val); >> rcu_read_unlock(); >=20 > Hm, but untracked pages are the rare exception. It would seem better > for that case to take the rcu_read_lock() unnecessarily, than it is to > look up folio->memcg_data twice in the fast path? Yep, you are right. I'll drop this next version. Thanks. Muchun, Thanks.