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[94.245.46.61]) by smtp.gmail.com with ESMTPSA id l8sm237631lfd.276.2021.01.20.08.21.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 20 Jan 2021 08:21:58 -0800 (PST) From: "Uladzislau Rezki (Sony)" To: LKML , RCU , "Paul E . McKenney" , Michael Ellerman Cc: Andrew Morton , Daniel Axtens , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Peter Zijlstra , Michal Hocko , Thomas Gleixner , "Theodore Y . Ts'o" , Sebastian Andrzej Siewior , Uladzislau Rezki , Oleksiy Avramchenko Subject: [PATCH 1/3] kvfree_rcu: Allocate a page for a single argument Date: Wed, 20 Jan 2021 17:21:46 +0100 Message-Id: <20210120162148.1973-1-urezki@gmail.com> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org For a single argument we can directly request a page from a caller context when a "carry page block" is run out of free spots. Instead of hitting a slow path we can request an extra page by demand and proceed with a fast path. A single-argument kvfree_rcu() must be invoked in sleepable contexts, and that its fallback is the relatively high latency synchronize_rcu(). Single-argument kvfree_rcu() therefore uses GFP_KERNEL|__GFP_RETRY_MAYFAIL to allow limited sleeping within the memory allocator. [ paulmck: Add add_ptr_to_bulk_krc_lock header comment per Michal Hocko. ] Signed-off-by: Uladzislau Rezki (Sony) Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 42 ++++++++++++++++++++++++++---------------- 1 file changed, 26 insertions(+), 16 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index e04e336bee42..2014fb22644d 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3465,37 +3465,50 @@ run_page_cache_worker(struct kfree_rcu_cpu *krcp) } } +// Record ptr in a page managed by krcp, with the pre-krc_this_cpu_lock() +// state specified by flags. If can_alloc is true, the caller must +// be schedulable and not be holding any locks or mutexes that might be +// acquired by the memory allocator or anything that it might invoke. +// Returns true if ptr was successfully recorded, else the caller must +// use a fallback. static inline bool -kvfree_call_rcu_add_ptr_to_bulk(struct kfree_rcu_cpu *krcp, void *ptr) +add_ptr_to_bulk_krc_lock(struct kfree_rcu_cpu **krcp, + unsigned long *flags, void *ptr, bool can_alloc) { struct kvfree_rcu_bulk_data *bnode; int idx; - if (unlikely(!krcp->initialized)) + *krcp = krc_this_cpu_lock(flags); + if (unlikely(!(*krcp)->initialized)) return false; - lockdep_assert_held(&krcp->lock); idx = !!is_vmalloc_addr(ptr); /* Check if a new block is required. */ - if (!krcp->bkvhead[idx] || - krcp->bkvhead[idx]->nr_records == KVFREE_BULK_MAX_ENTR) { - bnode = get_cached_bnode(krcp); - /* Switch to emergency path. */ + if (!(*krcp)->bkvhead[idx] || + (*krcp)->bkvhead[idx]->nr_records == KVFREE_BULK_MAX_ENTR) { + bnode = get_cached_bnode(*krcp); + if (!bnode && can_alloc) { + krc_this_cpu_unlock(*krcp, *flags); + bnode = (struct kvfree_rcu_bulk_data *) + __get_free_page(GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_NOWARN); + *krcp = krc_this_cpu_lock(flags); + } + if (!bnode) return false; /* Initialize the new block. */ bnode->nr_records = 0; - bnode->next = krcp->bkvhead[idx]; + bnode->next = (*krcp)->bkvhead[idx]; /* Attach it to the head. */ - krcp->bkvhead[idx] = bnode; + (*krcp)->bkvhead[idx] = bnode; } /* Finally insert. */ - krcp->bkvhead[idx]->records - [krcp->bkvhead[idx]->nr_records++] = ptr; + (*krcp)->bkvhead[idx]->records + [(*krcp)->bkvhead[idx]->nr_records++] = ptr; return true; } @@ -3533,8 +3546,6 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func) ptr = (unsigned long *) func; } - krcp = krc_this_cpu_lock(&flags); - // Queue the object but don't yet schedule the batch. if (debug_rcu_head_queue(ptr)) { // Probable double kfree_rcu(), just leak. @@ -3542,12 +3553,11 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func) __func__, head); // Mark as success and leave. - success = true; - goto unlock_return; + return; } kasan_record_aux_stack(ptr); - success = kvfree_call_rcu_add_ptr_to_bulk(krcp, ptr); + success = add_ptr_to_bulk_krc_lock(&krcp, &flags, ptr, !head); if (!success) { run_page_cache_worker(krcp); -- 2.20.1