On Fri, 21 Dec 2007 02:29:12 -0800
Andrew Morton <[email protected]> wrote:
> 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?
>
Indeed !
Thanks Andrew for taking the time and fixing my lazyness :(
Your version is much cleaner of course.
> 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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