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From: Qi Zheng In-Reply-To: <889581093179462979dbfb5458620fcca531787b.1784621804.git.zhengqi.arch@bytedance.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: D98191A0003 X-Rspam-User: X-Stat-Signature: 67jye8qyixqy3cuziq6iwnud8h7yb9bn X-Rspamd-Server: rspam04 X-HE-Tag: 1784625964-89751 X-HE-Meta: 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 DnftNh5+ DKdkyAcL++xrP1S6hM0B9mwjFEe4+ZuRS0gB+K67h0j9MmOUeLdRajkUirIHfYvimIjxfQZBuW6Vyk4ya0NN/M6iyn4z9ZN65zV+Zb4xyqw2bIMs46BovKMr28sCws6wUomR2A7mEd2Er3q2JuihvtUZ6IWqU4eRglzTFn6TwqLru02dYUS4tQRqB7FC4GMeTBDNx9MMEusm3rmtsWjbPERR/Rp/LhFUXbbCNVHghHmhIcBdQ5qcC4f9g091roUox2JVMvgf7aifRUVFvZ15HB1XHGOgHrl/nDJTC Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: sashiko left two review comments about this [1], but they look like false positives. [1]. https://sashiko.dev/#/patchset/cover.1784621804.git.zhengqi.arch%40bytedance.com > > +static bool is_shmem_unused_huge_match(struct folio *folio, > > + struct shrink_control *sc) > > +{ > > + struct mem_cgroup *memcg = NULL; > > + bool match; > > + > > + /* > > + * Only non-root memcg reclaim needs to match the folio charge against > > + * sc->memcg. Skip the folio memcg check for the following cases: > > + * 1. shmem quota reclaim (sc == NULL) > > + * 2. global shrinker reclaim > > + * 3. root memcg reclaim > > + */ > > + if (!sc || !sc->memcg || mem_cgroup_is_root(sc->memcg)) > > + return true; > > + > > + if (folio_nid(folio) != sc->nid) > > + return false; > > + > > + memcg = get_mem_cgroup_from_folio(folio); > > + match = memcg == sc->memcg; > Does this strict equality check fail when a memcg is offlined (reparented)? > When a memcg is offlined (e.g., a container exits), its list_lru items are > reparented to its online parent. During memory pressure, the parent memcg runs > its shrinker, making sc->memcg the parent. However, the folio remains charged > to the offline child memcg. > Consequently, get_mem_cgroup_from_folio() returns the offline child memcg, and > this strict equality check fails. No, get_mem_cgroup_from_folio() should returns parent memcg, not the child memcg. > > +static void shmem_unused_huge_requeue(struct inode *inode, struct folio *folio) > > +{ > > + struct shmem_inode_info *info = SHMEM_I(inode); > > + struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb); > > + struct mem_cgroup *memcg; > > + int nid = folio_nid(folio); > > + > > + memcg = shmem_unused_huge_alloc_lru(sbinfo, folio, GFP_NOWAIT); > > + if (IS_ERR(memcg)) > > + goto drop; > > + > > + spin_lock(&info->lock); > > + /* Requeue the inode to shrinklist */ > > + list_del_init(&info->shrinklist); > > + list_lru_add(&sbinfo->shrinklist, &info->shrinklist, nid, memcg); > > + info->shrinklist_memcg = memcg; > Can this cause a livelock under memory pressure? > Because the memcg match failed in is_shmem_unused_huge_match(), > shmem_unused_huge_shrink() calls this function to place the inode back on the > list. This attempts to requeue it using the offline child memcg. > list_lru_add() transparently routes it back to the parent's list, but > info->shrinklist_memcg records the child memcg. In the next shrinker pass, the > match fails again, creating an infinite requeue loop during reclaim. No, shmem_unused_huge_alloc_lru also returns the parent memcg: shmem_unused_huge_alloc_lru --> get_mem_cgroup_from_folio --> folio_memcg(folio) --> obj_cgroup_memcg(folio_objcg(folio)) --> objcg->memcg /* reparented to the parent memcg */