lkml.org 
[lkml]   [2005]   [Aug]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH] removes filp_count_lock and changes nr_files type to atomic_t
Christoph Hellwig a écrit :
> On Thu, Aug 25, 2005 at 11:17:23AM +0200, Eric Dumazet wrote:
>
>>>But that's not true. You need to write you own sysctl handler for it,
>>>probably worth adding a generic atomic_t sysctl handler while you're
>>>at it.
>>>
>>
>>I checked linux-2.6.13-rc7 tree, and atomic_read() is just a wrapper to
>>read v->counter.
>
>
> That doesn't matter. atomic_t is an opaqueue type and you must use the
> atomic_* interfaces to access it.

OK, here is a new clean patch that address this problem (nothing assumed about
atomics)

This patch removes filp_count_lock spinlock, used to protect files_stat.nr_files.

Introduce an atomic_t atomic_nr_files to keep the exact count, and mirror its
value into nr_files.

Forcing atomic_nr_files to be in the same cache line than nr_files makes sure
we dont dirty two cache lines.

There is still a locked memory operation on SMP, but it saves an sti/cli pair.

Thank you

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>

diff -Nru linux-2.6.13-rc7/fs/file_table.c linux-2.6.13-rc7-ed/fs/file_table.c
--- linux-2.6.13-rc7/fs/file_table.c 2005-08-24 05:39:14.000000000 +0200
+++ linux-2.6.13-rc7-ed/fs/file_table.c 2005-08-25 12:18:02.000000000 +0200
@@ -19,38 +19,28 @@
#include <linux/fsnotify.h>

/* sysctl tunables... */
-struct files_stat_struct files_stat = {
- .max_files = NR_FILE
-};
+struct files_stat_struct files_stat;

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);

/* slab constructors and destructors are called from arbitrary
- * context and must be fully threaded - use a local spinlock
- * to protect files_stat.nr_files
+ * context and must be fully threaded
*/
void filp_ctor(void * objp, struct kmem_cache_s *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);
+ files_stat.nr_files = atomic_add_return(1, &files_stat.atomic_nr_files);
}
}

void filp_dtor(void * objp, struct kmem_cache_s *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);
+ files_stat.nr_files = atomic_sub_return(1, &files_stat.atomic_nr_files);
}

static inline void file_free(struct file *f)
@@ -258,4 +248,5 @@
files_stat.max_files = n;
if (files_stat.max_files < NR_FILE)
files_stat.max_files = NR_FILE;
+ atomic_set(&files_stat.atomic_nr_files, 0);
}
diff -Nru linux-2.6.13-rc7/include/linux/fs.h linux-2.6.13-rc7-ed/include/linux/fs.h
--- linux-2.6.13-rc7/include/linux/fs.h 2005-08-24 05:39:14.000000000 +0200
+++ linux-2.6.13-rc7-ed/include/linux/fs.h 2005-08-25 12:39:07.000000000 +0200
@@ -9,6 +9,8 @@
#include <linux/config.h>
#include <linux/limits.h>
#include <linux/ioctl.h>
+#include <linux/cache.h>
+#include <asm/atomic.h>

/*
* It's silly to have NR_OPEN bigger than NR_FILE, but you can change
@@ -30,10 +32,12 @@

/* And dynamically-tunable limits and defaults: */
struct files_stat_struct {
- int nr_files; /* read only */
+ int nr_files; /* mirrors atomic_nr_files value */
int nr_free_files; /* read only */
int max_files; /* tunable */
-};
+
+ atomic_t atomic_nr_files;
+} ____cacheline_aligned;
extern struct files_stat_struct files_stat;

struct inodes_stat_t {
\
 
 \ /
  Last update: 2005-08-25 12:44    [W:0.052 / U:7.424 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site