From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792664852; b=dzLX8jZAnTYnBx2zLuuWlkTRbsaRt3vsptlmdz/rILIV5khJbf5omJxCbjHvUY4KkuDA vuB+xJEBsI+00jZ4idm3cXTuZ2gqBvLNb5VMNPF3xGc7/IqKi063JBxXLfP5bzVnLdFFL NaucMcNb1TUpty0HGSKocFrS01CogsR1Kdud5YKuZhTYidRPhUIjvlOKcSY0mqK8W7xXy 5jZiN1yDM4IlRQT3jiA87m2rRUPCqNl9b2uNbSMyR6TepXEVqeMGGfodKwAVVb3DV+TWe guiHCPZaVwuvaBvLOcTaUIl/ZcimPSPkKmF6SW7YXI9eUSXOuJSBZtmVu3pZ5eJ/gdg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792664852; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-Id:X-Mailer: In-Reply-To:References:MIME-Version:Content-Type: Content-Transfer-Encoding; bh=TgOOEpqKih5ogHRUxdmTCh2GDiwR8Qk5ZwygPDFgL2Q=; b=zVcdppIiW4sFHhgqE4D8i23kNTeX2nzr9W5IrZ7xDsRTnwIVu0wqXKVVDCsTfIV7Cz2W MykBkMQQpcij9OsQmQG4zsmZ8mP5ecmp/mDtOZ8xTEVe0baQbkgGltawWRI0Xo2YBJ3NK nKo7fOWGmeLD3OUF+cYPud7rTxiw7r2jQ+hCwwEVe1E5vW941brMWOWuPsktp+E70aTUy jLMROMwKmU5LUcetx8+KXfUUCLBIAHl0yS0vYVIwEyi85Brg/DFEQ1aqVKuBhD2gi1sMQ EufsiHSFUdV4Mv/fB43rASxhv2alvt5WUmbhJ2gkElJE4IHHgBu7eE+YxKD6ee84oYw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=CSWTZWHN; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 54D20606A31A for ; Thu, 22 Oct 2026 10:27:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=CSWTZWHN Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6B0F01F000C1; Thu, 22 Oct 2026 10:27:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792664851; bh=TgOOEpqKih5ogHRUxdmTCh2GDiwR8Qk5ZwygPDFgL2Q=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=CSWTZWHNAPgbOsZV8oU+qLEamweoNFqgirBvIl5wObWslAcgYViZzguK3G9viL4h0 ZEhIj+GxdH0NMm2E7gHROpgyO/RQ07LuvOLtwc1+NLrwmoTM6ry4q9D8seBEltQzkb Pw+pR0leUEOgDclcB8BVGOhGKvVMOdlgzLbIGdfF+lP0FZIxb8rY5jKQ3ax2zR7+Tk z58nK1YiONSh7y/NvYLhPu0YIpH6cwn0KFA0ItHux2S7JPt1cTOVKLgQd2oEP3jVkY xKAhuF1J0ADym5Y6HtHUn5TTf7YNAyynHZjYuPVEBqtoqP1kO7yJEFvSZ572lpWDz5 oYBE5SCUFxRFQ== From: "Barry Song (Xiaomi)" To: baolin.wang@linux.alibaba.com Cc: akpm@linux-foundation.org, axelrasmussen@google.com, baohua@kernel.org, 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 Subject: Re: [RFC PATCH v2] mm: vmscan: avoid anon scanning for GFP_NOIO with low swapcache in MGLRU Date: Thu, 22 Oct 2026 18:27:26 +0800 Message-Id: <20261022102726.56682-1-baohua@kernel.org> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: <0cbd219d-f69d-4f72-aec5-43e1f2d978de@linux.alibaba.com> References: <0cbd219d-f69d-4f72-aec5-43e1f2d978de@linux.alibaba.com> 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 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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. > > 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. 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? 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; + /* try to avoid aging, do gentle reclaim at the default priority */ if (sc->priority == DEF_PRIORITY) return false;