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Wed, 04 Mar 2026 20:45:54 -0800 (PST) MIME-Version: 1.0 References: <20260228161008.707-1-lenohou@gmail.com> <20260228212837.59661-1-21cnbao@gmail.com> <71281163-F081-456F-AFB0-37DC0470850A@icloud.com> In-Reply-To: <71281163-F081-456F-AFB0-37DC0470850A@icloud.com> From: Barry Song <21cnbao@gmail.com> Date: Thu, 5 Mar 2026 12:45:43 +0800 X-Gm-Features: AaiRm50jhwY8uCVcJhYNlLo-8R6Rm9EzauWp50Up2YRcFMIRedxN4_4Q_8ecdQM Message-ID: Subject: Re: [PATCH] mm/mglru: fix cgroup OOM during MGLRU state switching To: Bingfang Guo Cc: Yafang Shao , Axel Rasmussen , Yuanchu Xie , Kairui Song , BINGFANG GUO , lenohou@gmail.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, weixugc@google.com, wjl.linux@gmail.com, yuzhao@google.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: byamt6bjspocppxoz15srzha4yd1wxeu X-Rspamd-Server: rspam09 X-Rspam-User: X-Rspamd-Queue-Id: 1AC57160003 X-HE-Tag: 1772685955-510827 X-HE-Meta: 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 zFKETtVG 2EkVZHmXGWT4UT6y6ntw35nrisuZGjp9gbjDz73yaKrWXKXws+oIX8hH0xsSt7c+jxfIdrWyCy4MWPa2CFLaHYcfkd69Ma5TOS7M8VPE00EuvV1T7d5b/3vBzcOHk2DO/5tKkUGSI5lZeoqhJB9G0rsF7ahzCLFaFSBIaCgBTOP9KmZzwJh/Kx3EmLuVpideVZ36AKtbJ+BmNiLD9lZfhtWlQfn+tJUVCEomBOecxSo/lEpy1FySMK/hgNfDHLeAdw43mNnYQMETzj/uGqty593sHJHtsIToAC9Pdg3qSyLobgpHsu5MA9C9x1fUsPOZp326m0cZe4hY4QYb4V/T9ARs4uXuk1ZCbFRzvvOryaNc1+9RUJhPinS4eZmpjs+A5QTPT5hPPDRKcX0n6TSqzTC+OpClAk3Cr9LZRSwOm3fx7etc4bqBmLgRgg/TjkkyfRrs+zRj6eLKa1Z6tREJOBHCk0Q== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: [...] > > -- > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 614ccf39fe3f..d7ff7a6ed088 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -2652,6 +2652,43 @@ static bool can_age_anon_pages(struct lruvec *lruv= ec, > > #ifdef CONFIG_LRU_GEN > > +DEFINE_STATIC_KEY_FALSE(lru_gen_draining); > + > +static inline bool lru_gen_is_draining(void) > +{ > + return static_branch_unlikely(&lru_gen_draining); > +} > + > +/* > + * Lazily wait for the draining thread to finish if it's running. > + * > + * Return: whether we'd like to reclaim from multi-gen LRU. > + */ > +static inline bool lru_gen_draining_wait(struct lruvec *lruvec, struct s= can_control *sc) > +{ > + bool global_enabled =3D lru_gen_enabled(); > + > + /* Try reclaiming from the current LRU first */ > + if (sc->priority > DEF_PRIORITY / 2) > + return READ_ONCE(lruvec->lrugen.enabled); > + > + /* Oops, try from the other side... */ > + if (sc->priority > 1) > + return global_enabled; > + > + /* > + * If we see lrugen.enabled is consistent here, when we get the l= ru > + * spinlock, the migrating thread will have filled the lruvec wit= h some > + * pages, so we can continue without waiting. > + */ > + while (global_enabled ^ READ_ONCE(lruvec->lrugen.enabled)) { > + /* Not switching this one yet. Wait for a while. */ > + schedule_timeout_uninterruptible(1); > + } > + > + return global_enabled; > +} Hi Bingfang, Thanks very much for sharing. In my humble opinion, the code feels a bit hacky. If we need to do something to reduce the probability of OOM without fully fixing the issue, Leon=E2=80=99s approach=E2=80=94trying to r= eclaim from both MGLRU and the active/inactive LRU during the transition=E2=80=94seems less hacky, assuming they show the same likelihood of triggering OOM, while still leaving some race conditions there. > + > #ifdef CONFIG_LRU_GEN_ENABLED > DEFINE_STATIC_KEY_ARRAY_TRUE(lru_gen_caps, NR_LRU_GEN_CAPS); > #define get_cap(cap) static_branch_likely(&lru_gen_caps[cap]) > @@ -5171,6 +5208,8 @@ static void lru_gen_change_state(bool enabled) > if (enabled =3D=3D lru_gen_enabled()) > goto unlock; > > + static_branch_enable_cpuslocked(&lru_gen_draining); > + > if (enabled) > static_branch_enable_cpuslocked(&lru_gen_caps[LRU_GEN_COR= E]); > else > @@ -5201,6 +5240,9 @@ static void lru_gen_change_state(bool enabled) > > cond_resched(); > } while ((memcg =3D mem_cgroup_iter(NULL, memcg, NULL))); > + > + static_branch_disable_cpuslocked(&lru_gen_draining); > + > unlock: > mutex_unlock(&state_mutex); > put_online_mems(); > @@ -5752,6 +5794,16 @@ late_initcall(init_lru_gen); > > #else /* !CONFIG_LRU_GEN */ > > +static inline bool lru_gen_is_draining(void) > +{ > + return false; > +} > + > +static inline bool shrink_lruvec_draining(struct lruvec *lruvec, struct = scan_control *sc) > +{ > + return false; > +} > + > static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_cont= rol *sc) > { > BUILD_BUG(); > @@ -5780,7 +5832,10 @@ static void shrink_lruvec(struct lruvec *lruvec, s= truct scan_control *sc) > bool proportional_reclaim; > struct blk_plug plug; > > - if (lru_gen_enabled() && !root_reclaim(sc)) { > + if (lru_gen_is_draining() && lru_gen_draining_wait(lruvec, sc)) { > + lru_gen_shrink_lruvec(lruvec, sc); > + return; > + } else if (lru_gen_enabled() && !root_reclaim(sc)) { > lru_gen_shrink_lruvec(lruvec, sc); > return; > } Thanks Barry