On Thu, Aug 25, 2005 at 05:13:05PM +0200, Eric Dumazet wrote: > Nick Piggin a écrit : > > >OK, well I would prefer you do the proper atomic operations throughout > >where it "really matters" in file_table.c, and do your lazy synchronize > >with just the sysctl exported value. > > > > But... I got complains about atomic_read(&counter) being 'an atomic op' > (untrue), so my second patch just doesnt touch the path where nr_files was > read. >
Here is a patch that I had done some time ago that uses atomic_t, yet retains the sysctl handler. Eric, you earlier patch is incorrect exactly for that reason. One other thing - the claim that it removes filp_count_lock from fast path is bogus. The slab constructor/destructors are called only when we return the free file structs to the page allocator. That we don't do very often and therefore we don't acquire the lock - atleast not for every filp open and close. This is not to say we don't want a better reference counter like a per-cpu counter, but there is some difficult stuff there and the returns need to justify that. I would appreciate if you or anyone can demonstrate this to be a problem. The patch below was meant for debugging some suspected problems with -mm. Thanks Dipankar 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 <[EMAIL PROTECTED]> --- fs/dcache.c | 2 - fs/file_table.c | 71 ++++++++++++++++++++++++++----------------- fs/xfs/linux-2.6/xfs_linux.h | 3 + include/linux/file.h | 2 - include/linux/fs.h | 2 + kernel/sysctl.c | 5 ++- net/unix/af_unix.c | 2 - 7 files changed, 54 insertions(+), 33 deletions(-) diff -puN fs/file_table.c~files-scale-file-counting fs/file_table.c --- linux-2.6.13-rc3-mm3-fixes/fs/file_table.c~files-scale-file-counting 2005-08-09 12:24:27.000000000 +0530 +++ linux-2.6.13-rc3-mm3-fixes-dipankar/fs/file_table.c 2005-08-09 16:42:27.000000000 +0530 @@ -5,6 +5,7 @@ * Copyright (C) 1997 David S. Miller ([EMAIL PROTECTED]) */ +#include <linux/config.h> #include <linux/string.h> #include <linux/slab.h> #include <linux/file.h> @@ -18,52 +19,67 @@ #include <linux/mount.h> #include <linux/cdev.h> #include <linux/fsnotify.h> +#include <linux/sysctl.h> +#include <asm/atomic.h> /* 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); -static DEFINE_SPINLOCK(filp_count_lock); +static atomic_t 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_s *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_rcuhead); + kmem_cache_free(filp_cachep, f); } -void filp_dtor(void * objp, struct kmem_cache_s *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); + atomic_dec(&nr_files); + call_rcu(&f->f_rcuhead, file_free_rcu); } -static inline void file_free_rcu(struct rcu_head *head) +/* + * Return the total number of open files in the system + */ +int get_nr_files(void) { - struct file *f = container_of(head, struct file, f_rcuhead); - kmem_cache_free(filp_cachep, f); + return atomic_read(&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_rcuhead, file_free_rcu); + return files_stat.max_files; +} + +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) +{ + files_stat.nr_files = get_nr_files(); + 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 @@ -77,7 +93,7 @@ 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; @@ -97,11 +113,12 @@ struct file *get_empty_filp(void) /* f->f_version: 0 */ INIT_LIST_HEAD(&f->f_list); f->f_maxcount = INT_MAX; + 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; diff -puN include/linux/fs.h~files-scale-file-counting include/linux/fs.h --- linux-2.6.13-rc3-mm3-fixes/include/linux/fs.h~files-scale-file-counting 2005-08-09 15:52:14.000000000 +0530 +++ linux-2.6.13-rc3-mm3-fixes-dipankar/include/linux/fs.h 2005-08-09 16:59:05.000000000 +0530 @@ -36,6 +36,8 @@ 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 fs/xfs/linux-2.6/xfs_linux.h~files-scale-file-counting fs/xfs/linux-2.6/xfs_linux.h --- linux-2.6.13-rc3-mm3-fixes/fs/xfs/linux-2.6/xfs_linux.h~files-scale-file-counting 2005-08-09 15:58:51.000000000 +0530 +++ linux-2.6.13-rc3-mm3-fixes-dipankar/fs/xfs/linux-2.6/xfs_linux.h 2005-08-09 15:59:36.000000000 +0530 @@ -88,6 +88,7 @@ #include <linux/list.h> #include <linux/proc_fs.h> #include <linux/sort.h> +#include <linux/fs.h> #include <asm/page.h> #include <asm/div64.h> @@ -241,7 +242,7 @@ static inline void set_buffer_unwritten_ /* IRIX uses the current size of the name cache to guess a good value */ /* - this isn't the same but is a good enough starting point for now. */ -#define DQUOT_HASH_HEURISTIC files_stat.nr_files +#define DQUOT_HASH_HEURISTIC get_nr_files() /* IRIX inodes maintain the project ID also, zero this field on Linux */ #define DEFAULT_PROJID 0 diff -puN net/unix/af_unix.c~files-scale-file-counting net/unix/af_unix.c --- linux-2.6.13-rc3-mm3-fixes/net/unix/af_unix.c~files-scale-file-counting 2005-08-09 15:59:57.000000000 +0530 +++ linux-2.6.13-rc3-mm3-fixes-dipankar/net/unix/af_unix.c 2005-08-09 16:00:26.000000000 +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); diff -puN fs/dcache.c~files-scale-file-counting fs/dcache.c --- linux-2.6.13-rc3-mm3-fixes/fs/dcache.c~files-scale-file-counting 2005-08-09 16:00:50.000000000 +0530 +++ linux-2.6.13-rc3-mm3-fixes-dipankar/fs/dcache.c 2005-08-09 16:01:28.000000000 +0530 @@ -1895,7 +1895,7 @@ 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 include/linux/file.h~files-scale-file-counting include/linux/file.h --- linux-2.6.13-rc3-mm3-fixes/include/linux/file.h~files-scale-file-counting 2005-08-09 16:06:46.000000000 +0530 +++ linux-2.6.13-rc3-mm3-fixes-dipankar/include/linux/file.h 2005-08-09 16:07:33.000000000 +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_s; -extern void filp_ctor(void * objp, struct kmem_cache_s *cachep, unsigned long cflags); -extern void filp_dtor(void * objp, struct kmem_cache_s *cachep, unsigned long dflags); extern struct file ** alloc_fd_array(int); extern void free_fd_array(struct file **, int); diff -puN kernel/sysctl.c~files-scale-file-counting kernel/sysctl.c --- linux-2.6.13-rc3-mm3-fixes/kernel/sysctl.c~files-scale-file-counting 2005-08-09 16:21:27.000000000 +0530 +++ linux-2.6.13-rc3-mm3-fixes-dipankar/kernel/sysctl.c 2005-08-09 16:26:16.000000000 +0530 @@ -49,6 +49,9 @@ #include <linux/nfs_fs.h> #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. */ @@ -881,7 +884,7 @@ 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, _ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/