From 529bf6be5c04f2e869d07bfdb122e9fd98ade714 Mon Sep 17 00:00:00 2001 From: Dipankar Sarma Date: Tue, 7 Mar 2006 21:55:35 -0800 Subject: [PATCH] fix file counting I have benchmarked this on an x86_64 NUMA system and see no significant performance difference on kernbench. Tested on both x86_64 and powerpc. 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 percpu counter, 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 Cc: "Paul E. McKenney" Cc: "David S. Miller" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/file_table.c | 87 ++++++++++++++++++++++++++++++++++++--------------------- 1 file changed, 55 insertions(+), 32 deletions(-) (limited to 'fs/file_table.c') diff --git a/fs/file_table.c b/fs/file_table.c index 768b58167543..44fabeaa9415 100644 --- a/fs/file_table.c +++ b/fs/file_table.c @@ -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 + +#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 DEFINE_SPINLOCK(filp_count_lock); +static struct percpu_counter nr_files __cacheline_aligned_in_smp; -/* slab constructors and destructors are called from arbitrary - * context and must be fully threaded - use a local spinlock - * to protect files_stat.nr_files - */ -void filp_ctor(void *objp, struct kmem_cache *cachep, unsigned long cflags) +static inline void file_free_rcu(struct rcu_head *head) { - 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); - } + struct file *f = container_of(head, struct file, f_u.fu_rcuhead); + kmem_cache_free(filp_cachep, f); } -void filp_dtor(void *objp, struct kmem_cache *cachep, unsigned long dflags) +static inline void file_free(struct file *f) { - unsigned long flags; - spin_lock_irqsave(&filp_count_lock, flags); - files_stat.nr_files--; - spin_unlock_irqrestore(&filp_count_lock, flags); + percpu_counter_dec(&nr_files); + call_rcu(&f->f_u.fu_rcuhead, file_free_rcu); } -static inline void file_free_rcu(struct rcu_head *head) +/* + * Return the total number of open files in the system + */ +static int get_nr_files(void) { - struct file *f = container_of(head, struct file, f_u.fu_rcuhead); - kmem_cache_free(filp_cachep, f); + return percpu_counter_read_positive(&nr_files); } -static inline void file_free(struct file *f) +/* + * Return the maximum number of open files in the system + */ +int get_max_files(void) { - call_rcu(&f->f_u.fu_rcuhead, file_free_rcu); + return files_stat.max_files; } +EXPORT_SYMBOL_GPL(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) +{ + files_stat.nr_files = get_nr_files(); + return proc_dointvec(table, write, filp, buffer, lenp, ppos); +} +#else +int proc_nr_files(ctl_table *table, int write, struct file *filp, + void __user *buffer, size_t *lenp, loff_t *ppos) +{ + 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 @@ -78,14 +94,20 @@ struct file *get_empty_filp(void) /* * Privileged users can go above max_files */ - if (files_stat.nr_files >= files_stat.max_files && - !capable(CAP_SYS_ADMIN)) - goto over; + if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) { + /* + * percpu_counters are inaccurate. Do an expensive check before + * we go and fail. + */ + if (percpu_counter_sum(&nr_files) >= files_stat.max_files) + goto over; + } f = kmem_cache_alloc(filp_cachep, GFP_KERNEL); if (f == NULL) goto fail; + percpu_counter_inc(&nr_files); memset(f, 0, sizeof(*f)); if (security_file_alloc(f)) goto fail_sec; @@ -101,10 +123,10 @@ struct file *get_empty_filp(void) 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; @@ -276,4 +298,5 @@ void __init files_init(unsigned long mempages) if (files_stat.max_files < NR_FILE) files_stat.max_files = NR_FILE; files_defer_init(); + percpu_counter_init(&nr_files); } -- cgit v1.2.3