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Howlett" , SJ Park , Andrew Morton , Johannes Weiner , Qi Zheng , Ying Huang , Chris Li , Baoquan He , Nico Pache , Usama Arif , Michal Hocko , Roman Gushchin , Shakeel Butt , David Hildenbrand , Lorenzo Stoakes , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Vlastimil Babka , Suren Baghdasaryan , Kemeng Shi , Nhat Pham , Youngjun Park , Zi Yan , Gregory Price , "Matthew Wilcox (Oracle)" , Baolin Wang , Ryan Roberts , Dev Jain , Lance Yang , Hugh Dickins , David Rientjes , Yu Zhao , Vernon Yang , Zicheng Wang , Chen Ridong , Tal Zussman , Kairui Song , Xiang Liu , Ehab Ababneh , zhaozhengzhuo , Lian Wang , Kunwu Chan , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, damon@lists.linux.dev Content-Transfer-Encoding: quoted-printable Message-Id: <342E57E7-9B7F-4193-805E-D1EBB41299FF@linux.dev> References: <20261016-mglru-fg-v4-0-2106750c0bfa@tencent.com> <20261016-mglru-fg-v4-3-2106750c0bfa@tencent.com> To: kasong@tencent.com X-Mailer: Apple Mail (2.3901.100.1.1.12) X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 436A1C0003 X-Rspam-User: X-Stat-Signature: fwykae3yb9ficy46ux7c1bpdpce33b8u X-HE-Tag: 1792136374-418755 X-HE-Meta: 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 ezlOO8Ra P4kBcFtfwvxTTGOerDSeW7ytnc66FwDapS9jASp33amP5oEQr0cSH19bIAvcr3P/LMKOkwCGni+O2Wwoh9LReJG0UVlN7TJ47TZ41P+nknoY++JJ5QOax9HR85ZWuxreMVK4htbOnJyEAeYoKUZX6Lzp5egnbzQNptUJtn64M2QufuBnlgzTZu38qQCS9Hb7RhkE/nx4zTXBCguz6sNHsjXqLhabNNJ9p1g53Mlnimufc4kuXcOssVSR+XFuS3uv2nZxzOztUoRaEj5AjwE7tD+sS/rpqgB/H7yDXCrRBVfZBHeuz8bea2izfyTu50jNiioUsxy/tTe9xMlo7AkxRqKWEeWl+VUXWDWZuQ+wG3zd8SJEgxPs4DjDTeT6+az4TyKaWAx10pJi2k+sxdLgg6uTUT3AklGIApP82thNa1gz6tLHRbZ5skDgE9PjWeIeZpBCc Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > On Oct 16, 2026, at 02:15, Kairui Song via B4 Relay = wrote: >=20 > From: Kairui Song >=20 > Add a helper that resolves a stable lruvec for a folio under RCU > without taking the lruvec lock. It takes a folio directly so the > lruvec lookup happens inside the RCU read-side critical section, > which a lruvec-based interface cannot guarantee. >=20 > No functional change. >=20 > Tested-by: zhaozhengzhuo > Signed-off-by: Kairui Song > --- > include/linux/memcontrol.h | 39 = +++++++++++++++++++++++++++++++++++++++ > 1 file changed, 39 insertions(+) >=20 > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index 74110a324f9e..829ab776ab44 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -1535,6 +1535,45 @@ static inline void lruvec_lock_irq(struct = lruvec *lruvec) > spin_lock_irq(&lruvec->lru_lock); > } >=20 > +/** > + * folio_lruvec_live_get - get a live lruvec for a folio under RCU > + * @folio: the folio > + * > + * Computes @folio's lruvec and walks up to the nearest live ancestor > + * if the folio's memcg is dying. Paired with = folio_lruvec_live_put(). > + * The result may be stale: RCU keeps it alive but does not pin = @folio > + * to it. That is fine as the counters are fixed up on reparenting. > + * > + * Return: the live lruvec, with rcu_read_lock held. > + */ > +static inline struct lruvec *folio_lruvec_live_get(struct folio = *folio) > +{ > +#ifdef CONFIG_MEMCG > + struct lruvec *lruvec; > + struct pglist_data *pgdat; > + struct mem_cgroup *memcg; > + > + rcu_read_lock(); > + lruvec =3D folio_lruvec(folio); > + pgdat =3D lruvec_pgdat(lruvec); > + memcg =3D lruvec_memcg(lruvec); > + while (unlikely(memcg && css_is_dying(&memcg->css))) { > + memcg =3D parent_mem_cgroup(memcg); > + lruvec =3D mem_cgroup_lruvec(memcg, pgdat); > + } > + return lruvec; Hi Kairui, Actually, we don't have any means to guarantee that the memcg to which the returned lruvec belongs will not become dying after the return, right? > +#else > + return folio_lruvec(folio); Then, I'm wondering why folio_lruvec() doesn't apply to the memcg scenario. Internally, folio_lruvec() obtains the memcg through obj_cgroup_memcg(). So when the memcg becomes dying, it should be reparented to the parent memcg within a short time. Likewise, folio_lruvec() may also return an lruvec whose memcg may also be in a short-lived dying state. Since the results of the two are similar, why not just use folio_lruvec() directly? Or is there something I misunderstood? Thanks, Muchun > +#endif > +} > + > +static inline void folio_lruvec_live_put(struct lruvec *lruvec) > +{ > +#ifdef CONFIG_MEMCG > + rcu_read_unlock(); > +#endif > +} > + > static inline struct lruvec *lruvec_live_lock_irq(struct lruvec = *lruvec) > { > #ifdef CONFIG_MEMCG >=20 > --=20 > 2.56.0 >=20 >=20