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b=IVZyQmPp76a+wS5LUV2vl6e4XNku/IBMxUKBs48NG/VeMTUYenAQ330fp3e0RlHoH d/rdyTmCZO0RHe3OFbc23rCB299Db6q+7sH9n2jMfNYydI5HpuHqfBYRAQoedM5SUR 8L834n9zT9l+eAk/Mrrmn6CJ8s7LSwEpAB0sWHLDAqO3W0i3INfc2pIHnsPKs+2DRR 2M8SIQ9vP/69bddHVdbFapF+V3YUI7TJibfE7AJ5iyVQ44L/QmK35PkAO1LeQtBF95 fcDcsoc2JLaYhRjwzacfujmFlKBXPq/MWjehqMyUEmphZT05fdfiLBijGT961GcqLX zlZV2x43dzQjw== Message-ID: From: sashiko-bot@kernel.org Subject: Re: [PATCH v8 02/16] mm/mglru: extract lruvec_populated_min_seq() helper Reply-To: sashiko-reviews@lists.linux.dev To: =?utf-8?b?QmFycnkgU29uZyAoWGlhb21pKQ==?= , akpm@linux-foundation.org, linux-mm@kvack.org Cc: axelrasmussen@google.com, baolin.wang@linux.alibaba.com, baoquan.he@linux.dev, hannes@cmpxchg.org, hui.zhu@linux.dev, kasong@tencent.com, kunwu.chan@gmail.com, liam@infradead.org, lianux.mm@gmail.com, liuxiang.277@bytedance.com, lyugaofei@xiaomi.com, mhocko@kernel.org, mhocko@suse.com, qi.zheng@linux.dev, ridong.chen@linux.dev, rppt@kernel.org, ryncsn@gmail.com, shakeel.butt@linux.dev, surenb@google.com, wangzicheng@honor.com, weixugc@google.com, yuanchu@google.com, zhangbo56@xiaomi.com, zhuhui@kylinos.cn, sidchintamaneni@gmail.com In-Reply-To: <20261113185541.70203-3-baohua@kernel.org> References: <20261113185541.70203-1-baohua@kernel.org> <20261113185541.70203-3-baohua@kernel.org> Content-Type: text/plain; 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Sashiko AI review found 1 potential issue to consider: - [Low] mm/mglru: off-by-one loop bound in lruvec_populated_min_seq() -- commit 9751ca1c29ca665233058e3a3c3cfa85cc385872 Author: Kairui Song mm/mglru: extract lruvec_populated_min_seq() helper This commit extracts the search for the oldest populated generation of a given type from try_to_inc_min_seq() into a new lruvec_populated_min_seq() helper bounded by max_seq. > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 400f87fc51e12..27dfbd3ff02b3 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -3992,30 +3992,45 @@ static bool inc_min_seq(struct lruvec *lruvec, in= t type, int swappiness) > return true; > } > =20 > +/* Similar to lruvec_evictable_size, return the oldest populated seq of = the type */ > +static unsigned long lruvec_populated_min_seq(struct lruvec *lruvec, int= type, > + unsigned long max_seq) > +{ > + int gen, zone; > + unsigned long min_seq; > + struct lru_gen_folio *lrugen =3D &lruvec->lrugen; > + > + lockdep_assert_held(&lruvec->lru_lock); > + > + min_seq =3D READ_ONCE(lrugen->min_seq[type]); > + while (min_seq <=3D max_seq) { > + gen =3D lru_gen_from_seq(min_seq); > + for (zone =3D 0; zone < MAX_NR_ZONES; zone++) { > + if (!list_empty(&lrugen->folios[gen][type][zone])) > + return min_seq; > + } > + min_seq++; > + } > + > + return max_seq; > +} > + > static void try_to_inc_min_seq(struct lruvec *lruvec, int swappiness) > { > - int gen, type, zone; > + int type; > bool seq_inc_flag =3D false; > struct lru_gen_folio *lrugen =3D &lruvec->lrugen; > DEFINE_MIN_SEQ(lruvec); > + unsigned long seq; > =20 > VM_WARN_ON_ONCE(!seq_is_valid(lruvec)); > =20 > - /* find the oldest populated generation */ > + /* Requires at least MIN_NR_GENS gens for basic functionality */ > + seq =3D lrugen->max_seq - MIN_NR_GENS; > for_each_evictable_type(type, swappiness) { > - while (min_seq[type] + MIN_NR_GENS <=3D lrugen->max_seq) { > - gen =3D lru_gen_from_seq(min_seq[type]); > - > - for (zone =3D 0; zone < MAX_NR_ZONES; zone++) { > - if (!list_empty(&lrugen->folios[gen][type][zone])) > - goto next; > - } > - > - min_seq[type]++; > + min_seq[type] =3D lruvec_populated_min_seq(lruvec, type, seq + 1); > + if (min_seq[type] > lrugen->min_seq[type]) > seq_inc_flag =3D true; > - } > -next: > - ; > } [Severity: Low] Should lruvec_populated_min_seq() loop while (min_seq < max_seq) and return min_seq at the end? When min_seq =3D=3D max_seq, both the early return inside the loop and the final return evaluate to max_seq, so scanning all zones of generation seq + 1 under lruvec->lru_lock is redundant work that the original loop skipped. In addition, if lrugen->min_seq[type] > max_seq on entry (which happens in commit "mm/mglru: lift youngest gen protection for higher priority" when scan_folios() runs at DEF_PRIORITY while get_nr_gens() is MIN_NR_GENS), returning max_seq yields a sequence number below lrugen->min_seq[type]. --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20261113185541.7020= 3-1-baohua@kernel.org?part=3D2