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[PATCH] fix file counting

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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 <dipankar@in.ibm.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Dipankar Sarma 2006-03-07 21:55:35 -08:00 • committed by Linus Torvalds
parent 21a1ea9eb4
commit 529bf6be5c
6 changed files with 63 additions and 38 deletions
Download patch file Download diff file Expand all files Collapse all files

89
fs/file_table.c
View file

@ -5,6 +5,7 @@
* Copyright (C) 1997 David S. Miller (davem@caip.rutgers.edu)
*/
#include <linux/config.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/file.h>
@ -19,41 +20,20 @@
#include <linux/capability.h>
#include <linux/cdev.h>
#include <linux/fsnotify.h>
#include <linux/sysctl.h>
#include <linux/percpu_counter.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);
__cacheline_aligned_in_smp DEFINE_SPINLOCK(files_lock);
static DEFINE_SPINLOCK(filp_count_lock);
/* 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)
{
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);
}
}
void filp_dtor(void *objp, struct kmem_cache *cachep, unsigned long dflags)
{
unsigned long flags;
spin_lock_irqsave(&filp_count_lock, flags);
files_stat.nr_files--;
spin_unlock_irqrestore(&filp_count_lock, flags);
}
static struct percpu_counter nr_files __cacheline_aligned_in_smp;
static inline void file_free_rcu(struct rcu_head *head)
{
@ -63,9 +43,45 @@ static inline void file_free_rcu(struct rcu_head *head)
static inline void file_free(struct file *f)
{
percpu_counter_dec(&nr_files);
call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
}
/*
* Return the total number of open files in the system
*/
static int get_nr_files(void)
{
return percpu_counter_read_positive(&nr_files);
}
/*
* Return the maximum number of open files in the system
*/
int get_max_files(void)
{
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
* we run out of memory.
@ -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);
}