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smtp.subspace.kernel.org; dmarc=pass header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass header.d=linux.alibaba.com header.i=@linux.alibaba.com header.a=rsa-sha256 header.s=default header.b=ObOTgVLE; arc=none smtp.remote-ip=115.124.30.124 Received: from out30-124.freemail.mail.aliyun.com (out30-124.freemail.mail.aliyun.com [115.124.30.124]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 06A58606A319 for ; Thu, 22 Oct 2026 11:26:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 06A58606A319 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.a=rsa-sha256 header.s=default header.b=ObOTgVLE DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1792668388; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=wjJzAk76F+CxMgpyPLvq57N3yZotfosVsROZyeNCQWc=; b=ObOTgVLEL3GpiCLOj3TkwzlRr3AQ4UUpjR2Xp3MW7SddfjRhhr/8K0Hv0JjGTrRo7eIbn08nQzaIOj/XGyJiSiCVYpX0+mCXjhipvcvrxgvKx8IuXNoSThSJwyQ1VvlzdYhmzUVA1PainOb4jNZDw/AWpjqmhw4FhNM3pnW1nS4= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R261e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033045133197;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=17;SR=0;TI=SMTPD_---0XDJ5s7r_1792668386; Received: from 30.74.144.160(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0XDJ5s7r_1792668386 cluster:ay36) by smtp.aliyun-inc.com; Thu, 22 Oct 2026 19:26:27 +0800 Message-ID: Date: Thu, 22 Oct 2026 19:26:25 +0800 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v2] mm: vmscan: avoid anon scanning for GFP_NOIO with low swapcache in MGLRU To: "Barry Song (Xiaomi)" Cc: akpm@linux-foundation.org, axelrasmussen@google.com, baoquan.he@linux.dev, david@kernel.org, hannes@cmpxchg.org, kasong@tencent.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, liuxiang.277@bytedance.com, ljs@kernel.org, mhocko@kernel.org, qi.zheng@linux.dev, shakeel.butt@linux.dev, weixugc@google.com, yuanchu@google.com, zhangbo56@xiaomi.com References: <0cbd219d-f69d-4f72-aec5-43e1f2d978de@linux.alibaba.com> <20261022102726.56682-1-baohua@kernel.org> From: Baolin Wang In-Reply-To: <20261022102726.56682-1-baohua@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 10/22/26 6:27 PM, Barry Song (Xiaomi) wrote: > On Thu, Oct 22, 2026 at 4:49 PM Baolin Wang wrote: >> >> >> >> On 10/22/26 5:55 AM, Barry Song wrote: >>> On Wed, Oct 21, 2026 at 3:28 PM Baolin Wang >>> wrote: >>> [...] >>> >>>>> static bool lruvec_is_sizable(struct lruvec *lruvec, struct scan_control *sc) >>>>> { >>>>> unsigned long total; >>>>> int swappiness = get_swappiness(lruvec, sc); >>>>> struct mem_cgroup *memcg = lruvec_memcg(lruvec); >>>>> >>>>> + swappiness = get_scan_swappiness(lruvec, sc, swappiness); >>>>> + >>>>> total = lruvec_evictable_size(lruvec, swappiness); >>>>> >>>>> /* whether the size is big enough to be helpful */ >>>>> @@ -5249,9 +5265,10 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) >>>>> bool need_rotate = false, should_age = false; >>>>> long nr_batch, nr_to_scan; >>>>> int swappiness = get_swappiness(lruvec, sc); >>>>> + int scan_swappiness = get_scan_swappiness(lruvec, sc, swappiness); >>>> >>>> IMO, 'swappiness' and 'scan_swappiness' are really confusing. Why move >>>> this logic into get_swappiness()? In get_swappiness(), we already have >>>> some similar logic to adjust swappiness when there is no available swap >>>> space. >>>> >>> >>> Yes. It is very confusing. we can't do that in get_swappiness() as otherwise, >>> we will get cold/hot inversion due to GFP_NOIO. for a real swappiness=0, >>> we allow cold/hot inversion for anon, but for GFP_NOIO, this is not the >>> case. >> >> But can_reclaim_anon_pages() doesn't only handle the GFP_NOIO case, it >> also covers the swap space limitation scenario. The latter is what >> concerns me more. >> >> If we're only talking about the GFP_NOIO case, I'd agree with your >> concern. However, we could introduce a helper to force anon aging and >> add comments explaining why we need this. That would look more >> maintainable than 2 confusing swappiness variables, no? >> >> Just my 2 cents. >> >> Something like below (untested): >> >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index daa7e37c2236..7c1d26e6b9d7 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -2890,7 +2890,7 @@ static int get_swappiness(struct lruvec *lruvec, >> struct scan_control *sc) >> if (swappiness == SWAPPINESS_ANON_ONLY) >> return swappiness; >> >> - if (!sc->may_swap) >> + if (!sc->may_swap || !(sc->gfp_mask & __GFP_IO)) >> return 0; > > For GFP_NOIO, we should also check whether swapcache is low, since > GFP_NOIO can reclaim swapcache. We already have > reclaimable_anon_is_low() for this. Ah, yes, just a quick sample to show what I had in mind. :). Sould also consider reclaimable_anon_is_low() for the GFP_NOIO case. >> if (!can_demote(pgdat->node_id, sc, memcg) && >> @@ -4049,7 +4049,7 @@ static inline void flush_lru_batch(struct >> list_head *head, struct list_head **ba >> *batch_end = NULL; >> } >> >> -static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness) >> +static bool inc_min_seq(struct lruvec *lruvec, int type, int >> swappiness, bool force_anon_aging) >> { >> int zone; >> int remaining = MAX_LRU_BATCH; >> @@ -4063,7 +4063,7 @@ static bool inc_min_seq(struct lruvec *lruvec, int >> type, int swappiness) >> goto done; >> >> /* For anon type, skip the check if swappiness is zero (file >> only) */ >> - if (!type && !swappiness) >> + if (!type && !swappiness && !force_anon_aging) >> goto done; >> >> VM_WARN_ON_ONCE(get_nr_gens(lruvec, type) != MAX_NR_GENS); >> @@ -4183,7 +4183,20 @@ static void try_to_inc_min_seq(struct lruvec >> *lruvec, int swappiness) >> } >> } >> >> -static bool inc_max_seq(struct lruvec *lruvec, unsigned long seq, int >> swappiness) >> +static bool is_force_anon_aging(struct scan_control *sc, struct lruvec >> *lruvec, >> + int swappiness) >> +{ >> + if (swappiness || (sc->gfp_mask & __GFP_IO)) >> + return false; > > As above, GFP_NOIO doesn't imply swappiness=0 if there are many > swapcache folios to reclaim. So we should check > reclaimable_anon_is_low() here. > >> + >> + /* >> + * Explain why we neeed to force increase anon min seq. >> + * xxxxxx >> + */ >> + return swappiness != sc_swappiness(sc, lruvec_memcg(lruvec)); >> +} >> + >> +static bool inc_max_seq(struct lruvec *lruvec, unsigned long seq, int >> swappiness, bool force_anon_aging) >> { >> bool success; >> int prev, next; >> @@ -4205,7 +4218,7 @@ static bool inc_max_seq(struct lruvec *lruvec, >> unsigned long seq, int swappiness >> if (get_nr_gens(lruvec, type) != MAX_NR_GENS) >> continue; >> >> - if (inc_min_seq(lruvec, type, swappiness)) >> + if (inc_min_seq(lruvec, type, swappiness, force_anon_aging)) >> continue; >> >> lruvec_unlock_irq(lruvec); >> @@ -4249,7 +4262,7 @@ static bool inc_max_seq(struct lruvec *lruvec, >> unsigned long seq, int swappiness >> } >> >> static bool try_to_inc_max_seq(struct lruvec *lruvec, unsigned long seq, >> - int swappiness, bool force_scan) >> + int swappiness, bool force_scan, bool >> force_anon_aging) >> { >> bool success; >> struct lru_gen_mm_walk *walk; >> @@ -4260,7 +4273,7 @@ static bool try_to_inc_max_seq(struct lruvec >> *lruvec, unsigned long seq, >> VM_WARN_ON_ONCE(seq > READ_ONCE(lrugen->max_seq)); >> >> if (!mm_state) >> - return inc_max_seq(lruvec, seq, swappiness); >> + return inc_max_seq(lruvec, seq, swappiness, >> force_anon_aging); >> >> /* see the comment in iterate_mm_list() */ >> if (seq <= READ_ONCE(mm_state->seq)) >> @@ -4295,7 +4308,7 @@ static bool try_to_inc_max_seq(struct lruvec >> *lruvec, unsigned long seq, >> } while (mm); >> done: >> if (success) { >> - success = inc_max_seq(lruvec, seq, swappiness); >> + success = inc_max_seq(lruvec, seq, swappiness, >> force_anon_aging); >> WARN_ON_ONCE(!success); >> } >> >> @@ -5262,7 +5275,9 @@ static bool try_to_shrink_lruvec(struct lruvec >> *lruvec, struct scan_control *sc) >> } >> >> if (should_run_aging(lruvec, max_seq, sc, swappiness)) { >> - if (try_to_inc_max_seq(lruvec, max_seq, >> swappiness, false)) > > This is quite tricky. If we pass swappiness=0, anon aging will be > skipped. Do we want that for GFP_NOIO cases? I mean, these are not > real cases where anon aging should be disabled. No, we have real use cases where 'vm_swappiness' is set to 0, which means the workload never reclaims anon folios. So in this case we don't need to age anon folios. > static int should_skip_vma(unsigned long start, unsigned long end, struct mm_walk *args) > { > ... > if (vma == get_gate_vma(vma->vm_mm)) > return true; > ... > } > >> + bool force_anon_aging = is_force_anon_aging(sc, >> lruvec, swappiness); > > Adding a force_anon_aging argument to inc_max_seq() seems like > quite a burden. Maybe a cleaner approach is to pass sc all the > way to inc_max_seq() and let it detect GFP_NOIO cases itself? OK, still look good to me. > BTW, I guess we don't need to worry about swappiness at all. We can > simply bypass anon reclaim? > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index fc823fe3bd1f..fa6d9860156d 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -4903,6 +4903,8 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec, > int skipped = 0; > unsigned long remaining = nr_to_scan; > struct lru_gen_folio *lrugen = &lruvec->lrugen; > + struct pglist_data *pgdat = lruvec_pgdat(lruvec); > + struct mem_cgroup *memcg = lruvec_memcg(lruvec); > > VM_WARN_ON_ONCE(nr_to_scan > MAX_LRU_BATCH); > VM_WARN_ON_ONCE(!list_empty(list)); > @@ -4910,6 +4912,9 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec, > if (get_nr_gens(lruvec, type) == MIN_NR_GENS) > return 0; > > + if (!type && reclaimable_anon_is_low(memcg, pgdat->node_id, sc)) > + return 0; > + > gen = lru_gen_from_seq(lrugen->min_seq[type]); > > for (i = MAX_NR_ZONES; i > 0; i--) { > @@ -5164,12 +5169,19 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec, > static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq, > struct scan_control *sc, int swappiness) > { > + struct pglist_data *pgdat = lruvec_pgdat(lruvec); > + struct mem_cgroup *memcg = lruvec_memcg(lruvec); > DEFINE_MIN_SEQ(lruvec); > > /* have to run aging, since eviction is not possible anymore */ > if (evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS > max_seq) > return true; > > + /* run aging when GFP_NOIO limits anon reclaim with few swapcache folios */ > + if (swappiness && min_seq[LRU_GEN_FILE] + MIN_NR_GENS > max_seq && > + reclaimable_anon_is_low(memcg, pgdat->node_id, sc)) > + return true; I've considered this, but we'd still need to add some code in get_nr_to_scan()/lruvec_is_sizable() to filter out the anon folios for GFP_NOIO case. Rather than spreading the logic across multiple places, I'd prefer adding a helper with proper comments to handle the aging issue, like the sample code I showed.