On Fri, 14 Dec 2007 18:51:06 +0100 Eric Dumazet <[EMAIL PROTECTED]> wrote:
> We can use ilog2() in fs/namespace.c to compute hash_bits and hash_mask at
> compile time, not runtime.
Well noted.
> [namespace.patch text/plain (1.4KB)]
argh. (save-as, read, copy-paste, s/^/> /g)
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -25,6 +25,7 @@
> #include <linux/security.h>
> #include <linux/mount.h>
> #include <linux/ramfs.h>
> +#include <linux/log2.h>
> #include <asm/uaccess.h>
> #include <asm/unistd.h>
> #include "pnode.h"
> @@ -36,7 +37,8 @@ __cacheline_aligned_in_smp DEFINE_SPINLOCK(vfsmount_lock);
> static int event;
>
> static struct list_head *mount_hashtable __read_mostly;
> -static int hash_mask __read_mostly, hash_bits __read_mostly;
> +#define hash_bits ilog2(PAGE_SIZE / sizeof(struct list_head))
> +#define hash_mask ((1UL << hash_bits) - 1)
> static struct kmem_cache *mnt_cache __read_mostly;
> static struct rw_semaphore namespace_sem;
>
> @@ -1828,24 +1830,7 @@ void __init mnt_init(void)
> if (!mount_hashtable)
> panic("Failed to allocate mount hash table\n");
>
> - /*
> - * Find the power-of-two list-heads that can fit into the allocation..
> - * We don't guarantee that "sizeof(struct list_head)" is necessarily
> - * a power-of-two.
> - */
> - nr_hash = PAGE_SIZE / sizeof(struct list_head);
> - hash_bits = 0;
> - do {
> - hash_bits++;
> - } while ((nr_hash >> hash_bits) != 0);
> - hash_bits--;
> -
> - /*
> - * Re-calculate the actual number of entries and the mask
> - * from the number of bits we can fit.
> - */
> nr_hash = 1UL << hash_bits;
> - hash_mask = nr_hash - 1;
>
> printk("Mount-cache hash table entries: %d\n", nr_hash);
Those #defines you now have there are foul. Please, when there's a choice
between doing it minimally and doing it right, let's do it right?
Look what we can now do:
--- a/fs/namespace.c~use-ilog2-in-fs-namespacec-fix
+++ a/fs/namespace.c
@@ -31,14 +31,15 @@
#include "pnode.h"
#include "internal.h"
+#define HASH_SHIFT ilog2(PAGE_SIZE / sizeof(struct list_head))
+#define HASH_SIZE (1UL << HASH_SHIFT)
+
/* spinlock for vfsmount related operations, inplace of dcache_lock */
__cacheline_aligned_in_smp DEFINE_SPINLOCK(vfsmount_lock);
static int event;
static struct list_head *mount_hashtable __read_mostly;
-#define hash_bits ilog2(PAGE_SIZE / sizeof(struct list_head))
-#define hash_mask ((1UL << hash_bits) - 1)
static struct kmem_cache *mnt_cache __read_mostly;
static struct rw_semaphore namespace_sem;
@@ -50,8 +51,8 @@ static inline unsigned long hash(struct
{
unsigned long tmp = ((unsigned long)mnt / L1_CACHE_BYTES);
tmp += ((unsigned long)dentry / L1_CACHE_BYTES);
- tmp = tmp + (tmp >> hash_bits);
- return tmp & hash_mask;
+ tmp = tmp + (tmp >> HASH_SHIFT);
+ return tmp & (HASH_SIZE - 1);
}
struct vfsmount *alloc_vfsmnt(const char *name)
@@ -1815,9 +1816,7 @@ static void __init init_mount_tree(void)
void __init mnt_init(void)
{
- struct list_head *d;
- unsigned int nr_hash;
- int i;
+ unsigned u;
int err;
init_rwsem(&namespace_sem);
@@ -1830,18 +1829,11 @@ void __init mnt_init(void)
if (!mount_hashtable)
panic("Failed to allocate mount hash table\n");
- nr_hash = 1UL << hash_bits;
+ printk("Mount-cache hash table entries: %lu\n", HASH_SIZE);
- printk("Mount-cache hash table entries: %d\n", nr_hash);
+ for (u = 0; u < HASH_SIZE; u++)
+ INIT_LIST_HEAD(&mount_hashtable[u]);
- /* And initialize the newly allocated array */
- d = mount_hashtable;
- i = nr_hash;
- do {
- INIT_LIST_HEAD(d);
- d++;
- i--;
- } while (i);
err = sysfs_init();
if (err)
printk(KERN_WARNING "%s: sysfs_init error: %d\n",
_
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