Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751361AbWAZSnO (ORCPT ); Thu, 26 Jan 2006 13:43:14 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751364AbWAZSnN (ORCPT ); Thu, 26 Jan 2006 13:43:13 -0500 Received: from e33.co.us.ibm.com ([32.97.110.151]:385 "EHLO e33.co.us.ibm.com") by vger.kernel.org with ESMTP id S1751361AbWAZSnM (ORCPT ); Thu, 26 Jan 2006 13:43:12 -0500 Date: Fri, 27 Jan 2006 00:12:33 +0530 From: Dipankar Sarma To: Andrew Morton Cc: Linus Torvalds , "Paul E.McKenney" , linux-kernel@vger.kernel.org, Al Viro Subject: Re: [patch 2/2] fix file counting Message-ID: <20060126184233.GF4166@in.ibm.com> Reply-To: dipankar@in.ibm.com References: <20060126184010.GD4166@in.ibm.com> <20060126184127.GE4166@in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20060126184127.GE4166@in.ibm.com> User-Agent: Mutt/1.5.10i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 8626 Lines: 249 The way we do file struct accounting is not very suitable for batched freeing. For scalability reasons, file accounting was constructor/destructor based. This meant that nr_files was decremented only when the object was removed from the slab cache. This is susceptible to slab fragmentation. With RCU based file structure, consequent batched freeing and a test program like Serge's, we just speed this up and end up with a very fragmented slab - llm22:~ # cat /proc/sys/fs/file-nr 587730 0 758844 At the same time, I see only a 2000+ objects in filp cache. The following patch I fixes this problem. This patch changes the file counting by removing the filp_count_lock. Instead we use a separate atomic_t, nr_files, for now and all accesses to it are through get_nr_files() api. In the sysctl handler for nr_files, we populate files_stat.nr_files before returning to user. Counting files as an when they are created and destroyed (as opposed to inside slab) allows us to correctly count open files with RCU. Signed-off-by: Dipankar Sarma --- fs/dcache.c | 2 - fs/file_table.c | 79 ++++++++++++++++++++++++++++++--------------------- include/linux/file.h | 2 - include/linux/fs.h | 2 + kernel/sysctl.c | 5 ++- net/unix/af_unix.c | 2 - 6 files changed, 56 insertions(+), 36 deletions(-) diff -puN fs/dcache.c~fix-file-counting fs/dcache.c --- linux-2.6.16-rc1-rcu/fs/dcache.c~fix-file-counting 2006-01-26 00:38:47.000000000 +0530 +++ linux-2.6.16-rc1-rcu-dipankar/fs/dcache.c 2006-01-26 00:38:47.000000000 +0530 @@ -1734,7 +1734,7 @@ void __init vfs_caches_init(unsigned lon SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL); filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0, - SLAB_HWCACHE_ALIGN|SLAB_PANIC, filp_ctor, filp_dtor); + SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL); dcache_init(mempages); inode_init(mempages); diff -puN fs/file_table.c~fix-file-counting fs/file_table.c --- linux-2.6.16-rc1-rcu/fs/file_table.c~fix-file-counting 2006-01-26 00:38:47.000000000 +0530 +++ linux-2.6.16-rc1-rcu-dipankar/fs/file_table.c 2006-01-26 01:23:28.000000000 +0530 @@ -5,6 +5,7 @@ * Copyright (C) 1997 David S. Miller (davem@caip.rutgers.edu) */ +#include #include #include #include @@ -19,52 +20,67 @@ #include #include #include - +#include +#include + /* sysctl tunables... */ struct files_stat_struct files_stat = { .max_files = NR_FILE }; -EXPORT_SYMBOL(files_stat); /* Needed by unix.o */ - /* public. Not pretty! */ - __cacheline_aligned_in_smp DEFINE_SPINLOCK(files_lock); +__cacheline_aligned_in_smp DEFINE_SPINLOCK(files_lock); + +static atomic_t nr_files __cacheline_aligned_in_smp; -static DEFINE_SPINLOCK(filp_count_lock); +static inline void file_free_rcu(struct rcu_head *head) +{ + struct file *f = container_of(head, struct file, f_u.fu_rcuhead); + kmem_cache_free(filp_cachep, f); +} -/* slab constructors and destructors are called from arbitrary - * context and must be fully threaded - use a local spinlock - * to protect files_stat.nr_files +static inline void file_free(struct file *f) +{ + atomic_dec(&nr_files); + call_rcu(&f->f_u.fu_rcuhead, file_free_rcu); +} + +/* + * Return the total number of open files in the system */ -void filp_ctor(void *objp, struct kmem_cache *cachep, unsigned long cflags) +int get_nr_files(void) { - if ((cflags & (SLAB_CTOR_VERIFY|SLAB_CTOR_CONSTRUCTOR)) == - SLAB_CTOR_CONSTRUCTOR) { - unsigned long flags; - spin_lock_irqsave(&filp_count_lock, flags); - files_stat.nr_files++; - spin_unlock_irqrestore(&filp_count_lock, flags); - } + return atomic_read(&nr_files); } -void filp_dtor(void *objp, struct kmem_cache *cachep, unsigned long dflags) +/* + * Return the maximum number of open files in the system + */ +int get_max_files(void) { - unsigned long flags; - spin_lock_irqsave(&filp_count_lock, flags); - files_stat.nr_files--; - spin_unlock_irqrestore(&filp_count_lock, flags); + return files_stat.max_files; } -static inline void file_free_rcu(struct rcu_head *head) +EXPORT_SYMBOL(get_nr_files); +EXPORT_SYMBOL(get_max_files); + +/* + * Handle nr_files sysctl + */ +#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS) +int proc_nr_files(ctl_table *table, int write, struct file *filp, + void __user *buffer, size_t *lenp, loff_t *ppos) { - struct file *f = container_of(head, struct file, f_u.fu_rcuhead); - kmem_cache_free(filp_cachep, f); + files_stat.nr_files = get_nr_files(); + return proc_dointvec(table, write, filp, buffer, lenp, ppos); } - -static inline void file_free(struct file *f) +#else +int proc_nr_files(ctl_table *table, int write, struct file *filp, + void __user *buffer, size_t *lenp, loff_t *ppos) { - call_rcu(&f->f_u.fu_rcuhead, file_free_rcu); + return -ENOSYS; } +#endif /* Find an unused file structure and return a pointer to it. * Returns NULL, if there are no more free file structures or @@ -78,7 +94,7 @@ struct file *get_empty_filp(void) /* * Privileged users can go above max_files */ - if (files_stat.nr_files >= files_stat.max_files && + if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) goto over; @@ -97,14 +113,15 @@ struct file *get_empty_filp(void) rwlock_init(&f->f_owner.lock); /* f->f_version: 0 */ INIT_LIST_HEAD(&f->f_u.fu_list); + atomic_inc(&nr_files); return f; over: /* Ran out of filps - report that */ - if (files_stat.nr_files > old_max) { + if (get_nr_files() > old_max) { printk(KERN_INFO "VFS: file-max limit %d reached\n", - files_stat.max_files); - old_max = files_stat.nr_files; + get_max_files()); + old_max = get_nr_files(); } goto fail; diff -puN include/linux/file.h~fix-file-counting include/linux/file.h --- linux-2.6.16-rc1-rcu/include/linux/file.h~fix-file-counting 2006-01-26 00:38:47.000000000 +0530 +++ linux-2.6.16-rc1-rcu-dipankar/include/linux/file.h 2006-01-26 01:17:36.000000000 +0530 @@ -60,8 +60,6 @@ extern void put_filp(struct file *); extern int get_unused_fd(void); extern void FASTCALL(put_unused_fd(unsigned int fd)); struct kmem_cache; -extern void filp_ctor(void * objp, struct kmem_cache *cachep, unsigned long cflags); -extern void filp_dtor(void * objp, struct kmem_cache *cachep, unsigned long dflags); extern struct file ** alloc_fd_array(int); extern void free_fd_array(struct file **, int); diff -puN include/linux/fs.h~fix-file-counting include/linux/fs.h --- linux-2.6.16-rc1-rcu/include/linux/fs.h~fix-file-counting 2006-01-26 00:38:47.000000000 +0530 +++ linux-2.6.16-rc1-rcu-dipankar/include/linux/fs.h 2006-01-26 00:38:48.000000000 +0530 @@ -35,6 +35,8 @@ struct files_stat_struct { int max_files; /* tunable */ }; extern struct files_stat_struct files_stat; +extern int get_nr_files(void); +extern int get_max_files(void); struct inodes_stat_t { int nr_inodes; diff -puN kernel/sysctl.c~fix-file-counting kernel/sysctl.c --- linux-2.6.16-rc1-rcu/kernel/sysctl.c~fix-file-counting 2006-01-26 00:38:47.000000000 +0530 +++ linux-2.6.16-rc1-rcu-dipankar/kernel/sysctl.c 2006-01-26 00:38:48.000000000 +0530 @@ -52,6 +52,9 @@ #include #endif +extern int proc_nr_files(ctl_table *table, int write, struct file *filp, + void __user *buffer, size_t *lenp, loff_t *ppos); + #if defined(CONFIG_SYSCTL) /* External variables not in a header file. */ @@ -900,7 +903,7 @@ static ctl_table fs_table[] = { .data = &files_stat, .maxlen = 3*sizeof(int), .mode = 0444, - .proc_handler = &proc_dointvec, + .proc_handler = &proc_nr_files, }, { .ctl_name = FS_MAXFILE, diff -puN net/unix/af_unix.c~fix-file-counting net/unix/af_unix.c --- linux-2.6.16-rc1-rcu/net/unix/af_unix.c~fix-file-counting 2006-01-26 00:38:47.000000000 +0530 +++ linux-2.6.16-rc1-rcu-dipankar/net/unix/af_unix.c 2006-01-26 00:38:48.000000000 +0530 @@ -547,7 +547,7 @@ static struct sock * unix_create1(struct struct sock *sk = NULL; struct unix_sock *u; - if (atomic_read(&unix_nr_socks) >= 2*files_stat.max_files) + if (atomic_read(&unix_nr_socks) >= 2*get_max_files()) goto out; sk = sk_alloc(PF_UNIX, GFP_KERNEL, &unix_proto, 1); _ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/