From nobody Fri Feb 13 07:53:44 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EBC53E82CA1 for ; Wed, 27 Sep 2023 15:09:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232354AbjI0PJD (ORCPT ); Wed, 27 Sep 2023 11:09:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58892 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232336AbjI0PI7 (ORCPT ); Wed, 27 Sep 2023 11:08:59 -0400 Received: from out-203.mta1.migadu.com (out-203.mta1.migadu.com [IPv6:2001:41d0:203:375::cb]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B02F1139 for ; Wed, 27 Sep 2023 08:08:57 -0700 (PDT) X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1695827335; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=i5Ua/wdmvBo/wu1nXQ0Cl5cuox9DFv/B5F3hb3WMJFo=; b=Q8hMpLXlwyHYuhYTY7QmN3ucJ4BymSYDpw0OZAW82OI1HjO9QhUqV7hIgxRE3/+F1Zdf1X 9pwvp7A1SXynG+K4IEOnW40uYr4B8pTu6BDJ26Y+WSYnLIfaJXQFLXbhSCwQWYyEHZxai0 mR7jQfl6X8WWs0zHRyt6d4SZPcg5cVY= From: Roman Gushchin To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Johannes Weiner , Michal Hocko , Shakeel Butt , Muchun Song , Dennis Zhou , Andrew Morton , Roman Gushchin Subject: [PATCH rfc 1/5] mm: kmem: optimize get_obj_cgroup_from_current() Date: Wed, 27 Sep 2023 08:08:28 -0700 Message-ID: <20230927150832.335132-2-roman.gushchin@linux.dev> In-Reply-To: <20230927150832.335132-1-roman.gushchin@linux.dev> References: <20230927150832.335132-1-roman.gushchin@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Manually inline memcg_kmem_bypass() and active_memcg() to speed up get_obj_cgroup_from_current() by avoiding duplicate in_task() checks and active_memcg() readings. Also add a likely() macro to __get_obj_cgroup_from_memcg(): obj_cgroup_tryget() should succeed at almost all times except a very unlikely race with the memcg deletion path. Signed-off-by: Roman Gushchin (Cruise) Acked-by: Shakeel Butt --- mm/memcontrol.c | 34 ++++++++++++++-------------------- 1 file changed, 14 insertions(+), 20 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 9741d62d0424..16ac2a5838fb 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1068,19 +1068,6 @@ struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_= struct *mm) } EXPORT_SYMBOL(get_mem_cgroup_from_mm); =20 -static __always_inline bool memcg_kmem_bypass(void) -{ - /* Allow remote memcg charging from any context. */ - if (unlikely(active_memcg())) - return false; - - /* Memcg to charge can't be determined. */ - if (!in_task() || !current->mm || (current->flags & PF_KTHREAD)) - return true; - - return false; -} - /** * mem_cgroup_iter - iterate over memory cgroup hierarchy * @root: hierarchy root @@ -3007,7 +2994,7 @@ static struct obj_cgroup *__get_obj_cgroup_from_memcg= (struct mem_cgroup *memcg) =20 for (; !mem_cgroup_is_root(memcg); memcg =3D parent_mem_cgroup(memcg)) { objcg =3D rcu_dereference(memcg->objcg); - if (objcg && obj_cgroup_tryget(objcg)) + if (likely(objcg && obj_cgroup_tryget(objcg))) break; objcg =3D NULL; } @@ -3016,16 +3003,23 @@ static struct obj_cgroup *__get_obj_cgroup_from_mem= cg(struct mem_cgroup *memcg) =20 __always_inline struct obj_cgroup *get_obj_cgroup_from_current(void) { - struct obj_cgroup *objcg =3D NULL; struct mem_cgroup *memcg; + struct obj_cgroup *objcg; =20 - if (memcg_kmem_bypass()) - return NULL; + if (in_task()) { + memcg =3D current->active_memcg; + + /* Memcg to charge can't be determined. */ + if (likely(!memcg) && (!current->mm || (current->flags & PF_KTHREAD))) + return NULL; + } else { + memcg =3D this_cpu_read(int_active_memcg); + if (likely(!memcg)) + return NULL; + } =20 rcu_read_lock(); - if (unlikely(active_memcg())) - memcg =3D active_memcg(); - else + if (!memcg) memcg =3D mem_cgroup_from_task(current); objcg =3D __get_obj_cgroup_from_memcg(memcg); rcu_read_unlock(); --=20 2.42.0 From nobody Fri Feb 13 07:53:44 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0274DE82CA5 for ; Wed, 27 Sep 2023 15:09:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232362AbjI0PJF (ORCPT ); Wed, 27 Sep 2023 11:09:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58922 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232346AbjI0PJB (ORCPT ); Wed, 27 Sep 2023 11:09:01 -0400 Received: from out-192.mta1.migadu.com (out-192.mta1.migadu.com [IPv6:2001:41d0:203:375::c0]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D8C19191 for ; Wed, 27 Sep 2023 08:08:58 -0700 (PDT) X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1695827337; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Rcjc8iZxDm0DIYnvNFEg9AlvdD1o0gQiWksXrzSEaP4=; b=UsUhkDMLWoqWyU+5nbHGAFCVQZ5r2vg+XsHsShhnKPKLyiziXVyVxR9lcV7QyDWCZsJ8KL 7K/IZURrLDyBSSujwFVKE2aqWxPUYANqDoYmQ7nFA92KgzQTpifzj6n13nvCNmo4/FEFGw NyMkSUQBXz32JTg1sqlghlRIHfkR4f8= From: Roman Gushchin To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Johannes Weiner , Michal Hocko , Shakeel Butt , Muchun Song , Dennis Zhou , Andrew Morton , Roman Gushchin Subject: [PATCH rfc 2/5] mm: kmem: add direct objcg pointer to task_struct Date: Wed, 27 Sep 2023 08:08:29 -0700 Message-ID: <20230927150832.335132-3-roman.gushchin@linux.dev> In-Reply-To: <20230927150832.335132-1-roman.gushchin@linux.dev> References: <20230927150832.335132-1-roman.gushchin@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" To charge a freshly allocated kernel object to a memory cgroup, the kernel needs to obtain an objcg pointer. Currently it does it indirectly by obtaining the memcg pointer first and then calling to __get_obj_cgroup_from_memcg(). Usually tasks spend their entire life belonging to the same object cgroup. So it makes sense to save the objcg pointer on task_struct directly, so it can be obtained faster. It requires some work on fork, exit and cgroup migrate paths, but these paths are way colder. To avoid any costly synchronization the following rules are applied: 1) A task sets it's objcg pointer itself. 2) If a task is being migrated to another cgroup, the least significant bit of the objcg pointer is set. 3) On the allocation path the objcg pointer is obtained locklessly using the READ_ONCE() macro and the least significant bit is checked. If it set, the task updates it's objcg before proceeding with an allocation. 4) Operations 1) and 4) are synchronized via a new spinlock, so that if a task is moved twice, the update bit can't be lost. This allows to keep the hot path fully lockless. Because the task is keeping a reference to the objcg, it can't go away while the task is alive. This commit doesn't change the way the remote memcg charging works. Signed-off-by: Roman Gushchin (Cruise) --- include/linux/memcontrol.h | 10 ++++ include/linux/sched.h | 4 ++ mm/memcontrol.c | 107 +++++++++++++++++++++++++++++++++---- 3 files changed, 112 insertions(+), 9 deletions(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index ab94ad4597d0..84425bfe4124 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -553,6 +553,16 @@ static inline bool folio_memcg_kmem(struct folio *foli= o) return folio->memcg_data & MEMCG_DATA_KMEM; } =20 +static inline bool current_objcg_needs_update(struct obj_cgroup *objcg) +{ + return (struct obj_cgroup *)((unsigned long)objcg & 0x1); +} + +static inline struct obj_cgroup * +current_objcg_clear_update_flag(struct obj_cgroup *objcg) +{ + return (struct obj_cgroup *)((unsigned long)objcg & ~0x1); +} =20 #else static inline bool folio_memcg_kmem(struct folio *folio) diff --git a/include/linux/sched.h b/include/linux/sched.h index 77f01ac385f7..60de42715b56 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1443,6 +1443,10 @@ struct task_struct { struct mem_cgroup *active_memcg; #endif =20 +#ifdef CONFIG_MEMCG_KMEM + struct obj_cgroup *objcg; +#endif + #ifdef CONFIG_BLK_CGROUP struct gendisk *throttle_disk; #endif diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 16ac2a5838fb..7f33a503d600 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3001,6 +3001,47 @@ static struct obj_cgroup *__get_obj_cgroup_from_memc= g(struct mem_cgroup *memcg) return objcg; } =20 +static DEFINE_SPINLOCK(current_objcg_lock); + +static struct obj_cgroup *current_objcg_update(struct obj_cgroup *old) +{ + struct mem_cgroup *memcg; + struct obj_cgroup *objcg; + unsigned long flags; + + old =3D current_objcg_clear_update_flag(old); + if (old) + obj_cgroup_put(old); + + spin_lock_irqsave(¤t_objcg_lock, flags); + rcu_read_lock(); + memcg =3D mem_cgroup_from_task(current); + for (; memcg !=3D root_mem_cgroup; memcg =3D parent_mem_cgroup(memcg)) { + objcg =3D rcu_dereference(memcg->objcg); + if (objcg && obj_cgroup_tryget(objcg)) + break; + objcg =3D NULL; + } + rcu_read_unlock(); + + WRITE_ONCE(current->objcg, objcg); + spin_unlock_irqrestore(¤t_objcg_lock, flags); + + return objcg; +} + +static inline void current_objcg_set_needs_update(struct task_struct *task) +{ + struct obj_cgroup *objcg; + unsigned long flags; + + spin_lock_irqsave(¤t_objcg_lock, flags); + objcg =3D READ_ONCE(task->objcg); + objcg =3D (struct obj_cgroup *)((unsigned long)objcg | 0x1); + WRITE_ONCE(task->objcg, objcg); + spin_unlock_irqrestore(¤t_objcg_lock, flags); +} + __always_inline struct obj_cgroup *get_obj_cgroup_from_current(void) { struct mem_cgroup *memcg; @@ -3008,19 +3049,26 @@ __always_inline struct obj_cgroup *get_obj_cgroup_f= rom_current(void) =20 if (in_task()) { memcg =3D current->active_memcg; + if (unlikely(memcg)) + goto from_memcg; =20 - /* Memcg to charge can't be determined. */ - if (likely(!memcg) && (!current->mm || (current->flags & PF_KTHREAD))) - return NULL; + objcg =3D READ_ONCE(current->objcg); + if (unlikely(current_objcg_needs_update(objcg))) + objcg =3D current_objcg_update(objcg); + + if (objcg) { + obj_cgroup_get(objcg); + return objcg; + } } else { memcg =3D this_cpu_read(int_active_memcg); - if (likely(!memcg)) - return NULL; + if (unlikely(memcg)) + goto from_memcg; } + return NULL; =20 +from_memcg: rcu_read_lock(); - if (!memcg) - memcg =3D mem_cgroup_from_task(current); objcg =3D __get_obj_cgroup_from_memcg(memcg); rcu_read_unlock(); return objcg; @@ -6345,6 +6393,22 @@ static void mem_cgroup_move_task(void) mem_cgroup_clear_mc(); } } + +#ifdef CONFIG_MEMCG_KMEM +static void mem_cgroup_fork(struct task_struct *task) +{ + task->objcg =3D (struct obj_cgroup *)0x1; +} + +static void mem_cgroup_exit(struct task_struct *task) +{ + struct obj_cgroup *objcg =3D current_objcg_clear_update_flag(task->objcg); + + if (objcg) + obj_cgroup_put(objcg); +} +#endif + #else /* !CONFIG_MMU */ static int mem_cgroup_can_attach(struct cgroup_taskset *tset) { @@ -6359,7 +6423,7 @@ static void mem_cgroup_move_task(void) #endif =20 #ifdef CONFIG_LRU_GEN -static void mem_cgroup_attach(struct cgroup_taskset *tset) +static void mem_cgroup_lru_gen_attach(struct cgroup_taskset *tset) { struct task_struct *task; struct cgroup_subsys_state *css; @@ -6377,10 +6441,29 @@ static void mem_cgroup_attach(struct cgroup_taskset= *tset) task_unlock(task); } #else +static void mem_cgroup_lru_gen_attach(struct cgroup_taskset *tset) {} +#endif /* CONFIG_LRU_GEN */ + +#ifdef CONFIG_MEMCG_KMEM +static void mem_cgroup_kmem_attach(struct cgroup_taskset *tset) +{ + struct task_struct *task; + struct cgroup_subsys_state *css; + + cgroup_taskset_for_each(task, css, tset) + current_objcg_set_needs_update(task); +} +#else +static void mem_cgroup_kmem_attach(struct cgroup_taskset *tset) {} +#endif /* CONFIG_MEMCG_KMEM */ + +#if defined(CONFIG_LRU_GEN) || defined(CONFIG_MEMCG_KMEM) static void mem_cgroup_attach(struct cgroup_taskset *tset) { + mem_cgroup_lru_gen_attach(tset); + mem_cgroup_kmem_attach(tset); } -#endif /* CONFIG_LRU_GEN */ +#endif =20 static int seq_puts_memcg_tunable(struct seq_file *m, unsigned long value) { @@ -6824,9 +6907,15 @@ struct cgroup_subsys memory_cgrp_subsys =3D { .css_reset =3D mem_cgroup_css_reset, .css_rstat_flush =3D mem_cgroup_css_rstat_flush, .can_attach =3D mem_cgroup_can_attach, +#if defined(CONFIG_LRU_GEN) || defined(CONFIG_MEMCG_KMEM) .attach =3D mem_cgroup_attach, +#endif .cancel_attach =3D mem_cgroup_cancel_attach, .post_attach =3D mem_cgroup_move_task, +#ifdef CONFIG_MEMCG_KMEM + .fork =3D mem_cgroup_fork, + .exit =3D mem_cgroup_exit, +#endif .dfl_cftypes =3D memory_files, .legacy_cftypes =3D mem_cgroup_legacy_files, .early_init =3D 0, --=20 2.42.0 From nobody Fri Feb 13 07:53:44 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A91F5E82CA1 for ; Wed, 27 Sep 2023 15:09:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232376AbjI0PJH (ORCPT ); Wed, 27 Sep 2023 11:09:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59000 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232355AbjI0PJD (ORCPT ); Wed, 27 Sep 2023 11:09:03 -0400 Received: from out-201.mta1.migadu.com (out-201.mta1.migadu.com [IPv6:2001:41d0:203:375::c9]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 45E3B191 for ; Wed, 27 Sep 2023 08:09:01 -0700 (PDT) X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1695827339; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=NJPTphOT9Ah3iL7MZ9KbERD0ROIs5HQQzvQjuLNJnns=; b=pNocy6o9sigu+gpBp2nZU0nrp9UmQjhqPdMh8hND8MX7ixqhRzLWJmdV9/s/k8Rs1A5Qa5 6IMESlh4qTyehhfmr0rDc9in0xsrFhOJIDRwOsOUFW2sCFbjw/rB+qADTL7a3cw1BDr2Zq iq5OmF6L+8t6+ySa0+DaftZUm1opJI4= From: Roman Gushchin To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Johannes Weiner , Michal Hocko , Shakeel Butt , Muchun Song , Dennis Zhou , Andrew Morton , Roman Gushchin Subject: [PATCH rfc 3/5] mm: kmem: make memcg keep a reference to the original objcg Date: Wed, 27 Sep 2023 08:08:30 -0700 Message-ID: <20230927150832.335132-4-roman.gushchin@linux.dev> In-Reply-To: <20230927150832.335132-1-roman.gushchin@linux.dev> References: <20230927150832.335132-1-roman.gushchin@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Keep a reference to the original objcg object for the entire life of a memcg structure. This allows to simplify the synchronization on the kernel memory allocation paths: pinning a (live) memcg will also pin the corresponding objcg. The memory overhead of this change is minimal because object cgroups usually outlive their corresponding memory cgroups even without this change, so it's only an additional pointer per memcg. Signed-off-by: Roman Gushchin (Cruise) --- include/linux/memcontrol.h | 8 +++++++- mm/memcontrol.c | 5 +++++ 2 files changed, 12 insertions(+), 1 deletion(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 84425bfe4124..412ff0e8694d 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -299,7 +299,13 @@ struct mem_cgroup { =20 #ifdef CONFIG_MEMCG_KMEM int kmemcg_id; - struct obj_cgroup __rcu *objcg; + /* + * memcg->objcg is wiped out as a part of the objcg repaprenting + * process. memcg->orig_objcg preserves a pointer (and a reference) + * to the original objcg until the end of live of memcg. + */ + struct obj_cgroup __rcu *objcg; + struct obj_cgroup *orig_objcg; /* list of inherited objcgs, protected by objcg_lock */ struct list_head objcg_list; #endif diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 7f33a503d600..4815f897758c 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3803,6 +3803,8 @@ static int memcg_online_kmem(struct mem_cgroup *memcg) =20 objcg->memcg =3D memcg; rcu_assign_pointer(memcg->objcg, objcg); + obj_cgroup_get(objcg); + memcg->orig_objcg =3D objcg; =20 static_branch_enable(&memcg_kmem_online_key); =20 @@ -5297,6 +5299,9 @@ static void __mem_cgroup_free(struct mem_cgroup *memc= g) { int node; =20 + if (memcg->orig_objcg) + obj_cgroup_put(memcg->orig_objcg); + for_each_node(node) free_mem_cgroup_per_node_info(memcg, node); kfree(memcg->vmstats); --=20 2.42.0 From nobody Fri Feb 13 07:53:44 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9FF42E82CA1 for ; Wed, 27 Sep 2023 15:09:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232441AbjI0PJS (ORCPT ); Wed, 27 Sep 2023 11:09:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58990 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232336AbjI0PJE (ORCPT ); Wed, 27 Sep 2023 11:09:04 -0400 Received: from out-201.mta1.migadu.com (out-201.mta1.migadu.com [IPv6:2001:41d0:203:375::c9]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4779A1B1 for ; Wed, 27 Sep 2023 08:09:03 -0700 (PDT) X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1695827341; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=jeQJ/eIJXU0AYA9yk+s4aO7OKAgQk2qdJmGkoMOLMDk=; b=c6ZuccPLxLC+Ce4wWZ9aCvoGVbip0UFScbqDK/VCUHTzImAhP4V7Ea1dW8CIa6yy8rjLZJ 0Sp2j/SlVWnSus6gz0MlC0eiKozxqUtiaYSQ8bVhbIgA/srrcTqQNsoM1ecUX491WcPVhw WEyQ3zRkmTvotbuHgAt2bGqQFn9TnMI= From: Roman Gushchin To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Johannes Weiner , Michal Hocko , Shakeel Butt , Muchun Song , Dennis Zhou , Andrew Morton , Roman Gushchin Subject: [PATCH rfc 4/5] mm: kmem: scoped objcg protection Date: Wed, 27 Sep 2023 08:08:31 -0700 Message-ID: <20230927150832.335132-5-roman.gushchin@linux.dev> In-Reply-To: <20230927150832.335132-1-roman.gushchin@linux.dev> References: <20230927150832.335132-1-roman.gushchin@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Switch to a scope-based protection of the objcg pointer on slab/kmem allocation paths. Instead of using the get_() semantics in the pre-allocation hook and put the reference afterwards, let's rely on the fact that objcg is pinned by the scope. It's possible because: 1) if the objcg is received from the current task struct, the task is keeping a reference to the objcg. 2) if the objcg is received from an active memcg (remote charging), the memcg is pinned by the scope and has a reference to the corresponding objcg. Signed-off-by: Roman Gushchin (Cruise) --- include/linux/memcontrol.h | 6 +++++ mm/memcontrol.c | 46 ++++++++++++++++++++++++++++++++++++-- mm/slab.h | 10 +++------ 3 files changed, 53 insertions(+), 9 deletions(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 412ff0e8694d..9a5212d3b9d8 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -1779,6 +1779,12 @@ bool mem_cgroup_kmem_disabled(void); int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order); void __memcg_kmem_uncharge_page(struct page *page, int order); =20 +/* + * The returned objcg pointer is safe to use without additional + * protection within a scope, refer to the implementation for the + * additional details. + */ +struct obj_cgroup *current_obj_cgroup(void); struct obj_cgroup *get_obj_cgroup_from_current(void); struct obj_cgroup *get_obj_cgroup_from_folio(struct folio *folio); =20 diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 4815f897758c..76557370f212 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3074,6 +3074,48 @@ __always_inline struct obj_cgroup *get_obj_cgroup_fr= om_current(void) return objcg; } =20 +__always_inline struct obj_cgroup *current_obj_cgroup(void) +{ + struct mem_cgroup *memcg; + struct obj_cgroup *objcg; + + if (in_task()) { + memcg =3D current->active_memcg; + if (unlikely(memcg)) + goto from_memcg; + + objcg =3D READ_ONCE(current->objcg); + if (unlikely(current_objcg_needs_update(objcg))) + objcg =3D current_objcg_update(objcg); + /* + * Objcg reference is kept by the task, so it's safe + * to use the objcg by the current task. + */ + return objcg; + } else { + memcg =3D this_cpu_read(int_active_memcg); + if (unlikely(memcg)) + goto from_memcg; + } + return NULL; + +from_memcg: + for (; !mem_cgroup_is_root(memcg); memcg =3D parent_mem_cgroup(memcg)) { + /* + * Memcg pointer is protected by scope (see set_active_memcg()) + * and is pinning the corresponding objcg, so objcg can't go + * away and can be used within the scope without any additional + * protection. + */ + objcg =3D rcu_dereference_check(memcg->objcg, 1); + if (likely(objcg)) + break; + objcg =3D NULL; + } + + return objcg; +} + struct obj_cgroup *get_obj_cgroup_from_folio(struct folio *folio) { struct obj_cgroup *objcg; @@ -3168,15 +3210,15 @@ int __memcg_kmem_charge_page(struct page *page, gfp= _t gfp, int order) struct obj_cgroup *objcg; int ret =3D 0; =20 - objcg =3D get_obj_cgroup_from_current(); + objcg =3D current_obj_cgroup(); if (objcg) { ret =3D obj_cgroup_charge_pages(objcg, gfp, 1 << order); if (!ret) { + obj_cgroup_get(objcg); page->memcg_data =3D (unsigned long)objcg | MEMCG_DATA_KMEM; return 0; } - obj_cgroup_put(objcg); } return ret; } diff --git a/mm/slab.h b/mm/slab.h index 799a315695c6..8cd3294fedf5 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -484,7 +484,7 @@ static inline bool memcg_slab_pre_alloc_hook(struct kme= m_cache *s, if (!(flags & __GFP_ACCOUNT) && !(s->flags & SLAB_ACCOUNT)) return true; =20 - objcg =3D get_obj_cgroup_from_current(); + objcg =3D current_obj_cgroup(); if (!objcg) return true; =20 @@ -497,17 +497,14 @@ static inline bool memcg_slab_pre_alloc_hook(struct k= mem_cache *s, css_put(&memcg->css); =20 if (ret) - goto out; + return false; } =20 if (obj_cgroup_charge(objcg, flags, objects * obj_full_size(s))) - goto out; + return false; =20 *objcgp =3D objcg; return true; -out: - obj_cgroup_put(objcg); - return false; } =20 static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s, @@ -542,7 +539,6 @@ static inline void memcg_slab_post_alloc_hook(struct km= em_cache *s, obj_cgroup_uncharge(objcg, obj_full_size(s)); } } - obj_cgroup_put(objcg); } =20 static inline void memcg_slab_free_hook(struct kmem_cache *s, struct slab = *slab, --=20 2.42.0 From nobody Fri Feb 13 07:53:44 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C079BE82CA1 for ; Wed, 27 Sep 2023 15:09:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232414AbjI0PJX (ORCPT ); Wed, 27 Sep 2023 11:09:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56808 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232381AbjI0PJO (ORCPT ); Wed, 27 Sep 2023 11:09:14 -0400 Received: from out-193.mta1.migadu.com (out-193.mta1.migadu.com [IPv6:2001:41d0:203:375::c1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9D6811AC for ; Wed, 27 Sep 2023 08:09:07 -0700 (PDT) X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1695827344; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=j6TjL0tOzMm9uw8Y9niPXJ1ezOtPxfS6WilpL+cESRE=; b=V//ihQR3BNX8mCaIN2RHbsj24ybf5tsZR80ZurjIq/P4zdNE6/CNiqXGaUHELfnQzFCvFu ald/Rulhzhr/xKdfWTbsCyE4U6wbBWcnVys7yuOgrgVNmXQqA6dKbwvtqUzJLSfKLVSbkz VEv/GP4pB24vCqh16SVt3PIzQgO5+VI= From: Roman Gushchin To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Johannes Weiner , Michal Hocko , Shakeel Butt , Muchun Song , Dennis Zhou , Andrew Morton , Roman Gushchin Subject: [PATCH rfc 5/5] percpu: scoped objcg protection Date: Wed, 27 Sep 2023 08:08:32 -0700 Message-ID: <20230927150832.335132-6-roman.gushchin@linux.dev> In-Reply-To: <20230927150832.335132-1-roman.gushchin@linux.dev> References: <20230927150832.335132-1-roman.gushchin@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Similar to slab and kmem, switch to a scope-based protection of the objcg pointer to avoid. Signed-off-by: Roman Gushchin (Cruise) --- mm/percpu.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/mm/percpu.c b/mm/percpu.c index a7665de8485f..f53ba692d67a 100644 --- a/mm/percpu.c +++ b/mm/percpu.c @@ -1628,14 +1628,12 @@ static bool pcpu_memcg_pre_alloc_hook(size_t size, = gfp_t gfp, if (!memcg_kmem_online() || !(gfp & __GFP_ACCOUNT)) return true; =20 - objcg =3D get_obj_cgroup_from_current(); + objcg =3D current_obj_cgroup(); if (!objcg) return true; =20 - if (obj_cgroup_charge(objcg, gfp, pcpu_obj_full_size(size))) { - obj_cgroup_put(objcg); + if (obj_cgroup_charge(objcg, gfp, pcpu_obj_full_size(size))) return false; - } =20 *objcgp =3D objcg; return true; @@ -1649,6 +1647,7 @@ static void pcpu_memcg_post_alloc_hook(struct obj_cgr= oup *objcg, return; =20 if (likely(chunk && chunk->obj_cgroups)) { + obj_cgroup_get(objcg); chunk->obj_cgroups[off >> PCPU_MIN_ALLOC_SHIFT] =3D objcg; =20 rcu_read_lock(); @@ -1657,7 +1656,6 @@ static void pcpu_memcg_post_alloc_hook(struct obj_cgr= oup *objcg, rcu_read_unlock(); } else { obj_cgroup_uncharge(objcg, pcpu_obj_full_size(size)); - obj_cgroup_put(objcg); } } =20 --=20 2.42.0