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Fri, 9 Sep 2022 15:19:10 GMT Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id CD3644203F; Fri, 9 Sep 2022 15:19:10 +0000 (GMT) Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B500042042; Fri, 9 Sep 2022 15:19:09 +0000 (GMT) Received: from [9.145.83.17] (unknown [9.145.83.17]) by d06av24.portsmouth.uk.ibm.com (Postfix) with ESMTP; Fri, 9 Sep 2022 15:19:09 +0000 (GMT) Message-ID: <34dd5656-dc3c-6a20-5390-04d05c619fdc@linux.ibm.com> Date: Fri, 9 Sep 2022 17:19:09 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.2.1 Subject: Re: [RFC PATCH RESEND 28/28] kernel/fork: throttle call_rcu() calls in vm_area_free Content-Language: fr To: Suren Baghdasaryan , akpm@linux-foundation.org Cc: michel@lespinasse.org, jglisse@google.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mgorman@suse.de, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, peterz@infradead.org, laurent.dufour@fr.ibm.com, paulmck@kernel.org, luto@kernel.org, songliubraving@fb.com, peterx@redhat.com, david@redhat.com, dhowells@redhat.com, hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev, rientjes@google.com, axelrasmussen@google.com, joelaf@google.com, minchan@google.com, kernel-team@android.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, linux-kernel@vger.kernel.org References: <20220901173516.702122-1-surenb@google.com> <20220901173516.702122-29-surenb@google.com> From: Laurent Dufour In-Reply-To: <20220901173516.702122-29-surenb@google.com> Content-Type: text/plain; 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spf=pass (imf07.hostedemail.com: domain of ldufour@linux.ibm.com designates 148.163.158.5 as permitted sender) smtp.mailfrom=ldufour@linux.ibm.com; dmarc=pass (policy=none) header.from=ibm.com X-Stat-Signature: ofo71d7d6yxm16kf41wz73485gm1af3p X-Rspam-User: X-HE-Tag: 1662736766-450639 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Le 01/09/2022 à 19:35, Suren Baghdasaryan a écrit : > call_rcu() can take a long time when callback offloading is enabled. > Its use in the vm_area_free can cause regressions in the exit path when > multiple VMAs are being freed. To minimize that impact, place VMAs into > a list and free them in groups using one call_rcu() call per group. > > Signed-off-by: Suren Baghdasaryan > --- > include/linux/mm.h | 1 + > include/linux/mm_types.h | 11 ++++++- > kernel/fork.c | 68 +++++++++++++++++++++++++++++++++++----- > mm/init-mm.c | 3 ++ > mm/mmap.c | 1 + > 5 files changed, 75 insertions(+), 9 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index a3cbaa7b9119..81dff694ac14 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -249,6 +249,7 @@ void setup_initial_init_mm(void *start_code, void *end_code, > struct vm_area_struct *vm_area_alloc(struct mm_struct *); > struct vm_area_struct *vm_area_dup(struct vm_area_struct *); > void vm_area_free(struct vm_area_struct *); > +void drain_free_vmas(struct mm_struct *mm); > > #ifndef CONFIG_MMU > extern struct rb_root nommu_region_tree; > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index 36562e702baf..6f3effc493b1 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -412,7 +412,11 @@ struct vm_area_struct { > struct vm_area_struct *vm_next, *vm_prev; > }; > #ifdef CONFIG_PER_VMA_LOCK > - struct rcu_head vm_rcu; /* Used for deferred freeing. */ > + struct { > + struct list_head vm_free_list; > + /* Used for deferred freeing. */ > + struct rcu_head vm_rcu; > + }; > #endif > }; > > @@ -573,6 +577,11 @@ struct mm_struct { > */ > #ifdef CONFIG_PER_VMA_LOCK > int mm_lock_seq; > + struct { > + struct list_head head; > + spinlock_t lock; > + int size; > + } vma_free_list; > #endif > > > diff --git a/kernel/fork.c b/kernel/fork.c > index b443ba3a247a..7c88710aed72 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -483,26 +483,75 @@ struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig) > } > > #ifdef CONFIG_PER_VMA_LOCK > -static void __vm_area_free(struct rcu_head *head) > +static inline void __vm_area_free(struct vm_area_struct *vma) > { > - struct vm_area_struct *vma = container_of(head, struct vm_area_struct, > - vm_rcu); > /* The vma should either have no lock holders or be write-locked. */ > vma_assert_no_reader(vma); > kmem_cache_free(vm_area_cachep, vma); > } > -#endif > + > +static void vma_free_rcu_callback(struct rcu_head *head) > +{ > + struct vm_area_struct *first_vma; > + struct vm_area_struct *vma, *vma2; > + > + first_vma = container_of(head, struct vm_area_struct, vm_rcu); > + list_for_each_entry_safe(vma, vma2, &first_vma->vm_free_list, vm_free_list) Is that safe to walk the list against concurrent calls to list_splice_init(), or list_add()? > + __vm_area_free(vma); > + __vm_area_free(first_vma); > +} > + > +void drain_free_vmas(struct mm_struct *mm) > +{ > + struct vm_area_struct *first_vma; > + LIST_HEAD(to_destroy); > + > + spin_lock(&mm->vma_free_list.lock); > + list_splice_init(&mm->vma_free_list.head, &to_destroy); > + mm->vma_free_list.size = 0; > + spin_unlock(&mm->vma_free_list.lock); > + > + if (list_empty(&to_destroy)) > + return; > + > + first_vma = list_first_entry(&to_destroy, struct vm_area_struct, vm_free_list); > + /* Remove the head which is allocated on the stack */ > + list_del(&to_destroy); > + > + call_rcu(&first_vma->vm_rcu, vma_free_rcu_callback); > +} > + > +#define VM_AREA_FREE_LIST_MAX 32 > + > +void vm_area_free(struct vm_area_struct *vma) > +{ > + struct mm_struct *mm = vma->vm_mm; > + bool drain; > + > + free_anon_vma_name(vma); > + > + spin_lock(&mm->vma_free_list.lock); > + list_add(&vma->vm_free_list, &mm->vma_free_list.head); > + mm->vma_free_list.size++; > + drain = mm->vma_free_list.size > VM_AREA_FREE_LIST_MAX; > + spin_unlock(&mm->vma_free_list.lock); > + > + if (drain) > + drain_free_vmas(mm); > +} > + > +#else /* CONFIG_PER_VMA_LOCK */ > + > +void drain_free_vmas(struct mm_struct *mm) {} > > void vm_area_free(struct vm_area_struct *vma) > { > free_anon_vma_name(vma); > -#ifdef CONFIG_PER_VMA_LOCK > - call_rcu(&vma->vm_rcu, __vm_area_free); > -#else > kmem_cache_free(vm_area_cachep, vma); > -#endif > } > > +#endif /* CONFIG_PER_VMA_LOCK */ > + > static void account_kernel_stack(struct task_struct *tsk, int account) > { > if (IS_ENABLED(CONFIG_VMAP_STACK)) { > @@ -1137,6 +1186,9 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p, > INIT_LIST_HEAD(&mm->mmlist); > #ifdef CONFIG_PER_VMA_LOCK > WRITE_ONCE(mm->mm_lock_seq, 0); > + INIT_LIST_HEAD(&mm->vma_free_list.head); > + spin_lock_init(&mm->vma_free_list.lock); > + mm->vma_free_list.size = 0; > #endif > mm_pgtables_bytes_init(mm); > mm->map_count = 0; > diff --git a/mm/init-mm.c b/mm/init-mm.c > index 8399f90d631c..7b6d2460545f 100644 > --- a/mm/init-mm.c > +++ b/mm/init-mm.c > @@ -39,6 +39,9 @@ struct mm_struct init_mm = { > .mmlist = LIST_HEAD_INIT(init_mm.mmlist), > #ifdef CONFIG_PER_VMA_LOCK > .mm_lock_seq = 0, > + .vma_free_list.head = LIST_HEAD_INIT(init_mm.vma_free_list.head), > + .vma_free_list.lock = __SPIN_LOCK_UNLOCKED(init_mm.vma_free_list.lock), > + .vma_free_list.size = 0, > #endif > .user_ns = &init_user_ns, > .cpu_bitmap = CPU_BITS_NONE, > diff --git a/mm/mmap.c b/mm/mmap.c > index 1edfcd384f5e..d61b7ef84ba6 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -3149,6 +3149,7 @@ void exit_mmap(struct mm_struct *mm) > } > mm->mmap = NULL; > mmap_write_unlock(mm); > + drain_free_vmas(mm); > vm_unacct_memory(nr_accounted); > } >