From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f71.google.com (mail-lf0-f71.google.com [209.85.215.71]) by kanga.kvack.org (Postfix) with ESMTP id 40FBF6B000A for ; Sun, 24 Jun 2018 16:09:12 -0400 (EDT) Received: by mail-lf0-f71.google.com with SMTP id a131-v6so3367182lfe.1 for ; Sun, 24 Jun 2018 13:09:12 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id w3-v6sor2546700ljh.32.2018.06.24.13.09.10 for (Google Transport Security); Sun, 24 Jun 2018 13:09:10 -0700 (PDT) Date: Sun, 24 Jun 2018 23:09:07 +0300 From: Vladimir Davydov Subject: Re: [PATCH 3/3] mm: list_lru: Add lock_irq member to __list_lru_init() Message-ID: <20180624200907.ufjxk6l2biz6xcm2@esperanza> References: <20180622151221.28167-1-bigeasy@linutronix.de> <20180622151221.28167-4-bigeasy@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180622151221.28167-4-bigeasy@linutronix.de> Sender: owner-linux-mm@kvack.org List-ID: To: Sebastian Andrzej Siewior Cc: linux-mm@kvack.org, tglx@linutronix.de, Andrew Morton On Fri, Jun 22, 2018 at 05:12:21PM +0200, Sebastian Andrzej Siewior wrote: > scan_shadow_nodes() is the only user of __list_lru_walk_one() which > disables interrupts before invoking it. The reason is that nlru->lock is > nesting inside IRQ-safe i_pages lock. Some functions unconditionally > acquire the lock with the _irq() suffix. > > __list_lru_walk_one() can't acquire the lock unconditionally with _irq() > suffix because it might invoke a callback which unlocks the nlru->lock > and invokes a sleeping function without enabling interrupts. > > Add an argument to __list_lru_init() which identifies wheather the > nlru->lock needs to be acquired with disabling interrupts or without. > > Signed-off-by: Sebastian Andrzej Siewior > --- > include/linux/list_lru.h | 12 ++++++++---- > mm/list_lru.c | 14 ++++++++++---- > mm/workingset.c | 12 ++++-------- > 3 files changed, 22 insertions(+), 16 deletions(-) > > diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h > index 96def9d15b1b..c2161c3a1809 100644 > --- a/include/linux/list_lru.h > +++ b/include/linux/list_lru.h > @@ -51,18 +51,22 @@ struct list_lru_node { > > struct list_lru { > struct list_lru_node *node; > + bool lock_irq; > #if defined(CONFIG_MEMCG) && !defined(CONFIG_SLOB) > struct list_head list; > #endif > }; TBO I don't like this patch, because the new member of struct list_lru, lock_irq, has rather obscure meaning IMHO: it makes list_lru_walk disable irq before taking lru_lock, but at the same time list_lru_add and list_lru_del never do that, no matter whether lock_irq is true or false. That is, if a user of struct list_lru sets this flag, he's supposed to disable irq for list_lru_add/del by himself (mm/workingset does that). IMHO the code of mm/workingset is clear as it is. Since it is the only place where this flag is used, I'd rather leave it as is. > > void list_lru_destroy(struct list_lru *lru); > -int __list_lru_init(struct list_lru *lru, bool memcg_aware, > +int __list_lru_init(struct list_lru *lru, bool memcg_aware, bool lock_irq, > struct lock_class_key *key); > > -#define list_lru_init(lru) __list_lru_init((lru), false, NULL) > -#define list_lru_init_key(lru, key) __list_lru_init((lru), false, (key)) > -#define list_lru_init_memcg(lru) __list_lru_init((lru), true, NULL) > +#define list_lru_init(lru) __list_lru_init((lru), false, false, \ > + NULL) > +#define list_lru_init_key(lru, key) __list_lru_init((lru), false, false, \ > + (key)) > +#define list_lru_init_memcg(lru) __list_lru_init((lru), true, false, \ > + NULL) > > int memcg_update_all_list_lrus(int num_memcgs); > void memcg_drain_all_list_lrus(int src_idx, int dst_idx); > diff --git a/mm/list_lru.c b/mm/list_lru.c > index fcfb6c89ed47..1c49d48078e4 100644 > --- a/mm/list_lru.c > +++ b/mm/list_lru.c > @@ -204,7 +204,10 @@ __list_lru_walk_one(struct list_lru *lru, int nid, int memcg_idx, > struct list_head *item, *n; > unsigned long isolated = 0; > > - spin_lock(&nlru->lock); > + if (lru->lock_irq) > + spin_lock_irq(&nlru->lock); > + else > + spin_lock(&nlru->lock); > l = list_lru_from_memcg_idx(nlru, memcg_idx); > restart: > list_for_each_safe(item, n, &l->list) { > @@ -251,7 +254,10 @@ __list_lru_walk_one(struct list_lru *lru, int nid, int memcg_idx, > } > } > > - spin_unlock(&nlru->lock); > + if (lru->lock_irq) > + spin_unlock_irq(&nlru->lock); > + else > + spin_unlock(&nlru->lock); > return isolated; > } > > @@ -553,7 +559,7 @@ static void memcg_destroy_list_lru(struct list_lru *lru) > } > #endif /* CONFIG_MEMCG && !CONFIG_SLOB */ > > -int __list_lru_init(struct list_lru *lru, bool memcg_aware, > +int __list_lru_init(struct list_lru *lru, bool memcg_aware, bool lock_irq, > struct lock_class_key *key) > { > int i; > @@ -580,7 +586,7 @@ int __list_lru_init(struct list_lru *lru, bool memcg_aware, > lru->node = NULL; > goto out; > } > - > + lru->lock_irq = lock_irq; > list_lru_register(lru); > out: > memcg_put_cache_ids(); > diff --git a/mm/workingset.c b/mm/workingset.c > index 529480c21f93..23ce00f48212 100644 > --- a/mm/workingset.c > +++ b/mm/workingset.c > @@ -480,13 +480,8 @@ static enum lru_status shadow_lru_isolate(struct list_head *item, > static unsigned long scan_shadow_nodes(struct shrinker *shrinker, > struct shrink_control *sc) > { > - unsigned long ret; > - > - /* list_lru lock nests inside the IRQ-safe i_pages lock */ > - local_irq_disable(); > - ret = list_lru_shrink_walk(&shadow_nodes, sc, shadow_lru_isolate, NULL); > - local_irq_enable(); > - return ret; > + return list_lru_shrink_walk(&shadow_nodes, sc, shadow_lru_isolate, > + NULL); > } > > static struct shrinker workingset_shadow_shrinker = { > @@ -523,7 +518,8 @@ static int __init workingset_init(void) > pr_info("workingset: timestamp_bits=%d max_order=%d bucket_order=%u\n", > timestamp_bits, max_order, bucket_order); > > - ret = __list_lru_init(&shadow_nodes, true, &shadow_nodes_key); > + /* list_lru lock nests inside the IRQ-safe i_pages lock */ > + ret = __list_lru_init(&shadow_nodes, true, true, &shadow_nodes_key); > if (ret) > goto err; > ret = register_shrinker(&workingset_shadow_shrinker);