On 7/13/07, Kirill Korotaev <[email protected]> wrote:
This doesn't look worth zeroing half of the struct
when it is initialized to non-zeros then.
But why?
My reason to think it's better and faster is that:
1. the code will be shorter if it calls zalloc and then removes the
NULL and zero initilization;
2. in the assembly code objdumped, many mov operations reduced, such as:
movl $0,0x40(%ebp)
...
this style of zero initialization occupies 7 bytes per line
(i386), and then multiply 7 lines,
3. the only change is that calls to kmem_cache_zalloc other than
kmem_cache_alloc, it's just an extra memset is called, as we all know
the memset implimentation is string operation, that's rather fast.
Denis Cheng wrote:
>>From 4d87e14b67890f06885a76b5792ca034de2e9d06 Mon Sep 17 00:00:00 2001
> From: Denis Cheng <[email protected]>
> Date: Thu, 12 Jul 2007 11:53:58 +0800
> Subject: [PATCH] replace kmem_cache_alloc with kmem_cache_zalloc to
> remove some following zero initializations.
>
> Signed-off-by: Denis Cheng <[email protected]>
> ---
> fs/dcache.c | 12 ++----------
> 1 files changed, 2 insertions(+), 10 deletions(-)
>
> diff --git a/fs/dcache.c b/fs/dcache.c
> index 0e73aa0..8c559b2 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -898,7 +898,7 @@ struct dentry *d_alloc(struct dentry * parent, const
> struct qstr *name)
> struct dentry *dentry;
> char *dname;
>
> - dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL);
> + dentry = kmem_cache_zalloc(dentry_cache, GFP_KERNEL);
> if (!dentry)
> return NULL;
>
> @@ -921,15 +921,7 @@ struct dentry *d_alloc(struct dentry * parent,
> const struct qstr *name)
> atomic_set(&dentry->d_count, 1);
> dentry->d_flags = DCACHE_UNHASHED;
> spin_lock_init(&dentry->d_lock);
> - dentry->d_inode = NULL;
> - dentry->d_parent = NULL;
> - dentry->d_sb = NULL;
> - dentry->d_op = NULL;
> - dentry->d_fsdata = NULL;
> - dentry->d_mounted = 0;
> -#ifdef CONFIG_PROFILING
> - dentry->d_cookie = NULL;
> -#endif
> +
> INIT_HLIST_NODE(&dentry->d_hash);
> INIT_LIST_HEAD(&dentry->d_lru);
> INIT_LIST_HEAD(&dentry->d_subdirs);
--
Denis Cheng
Linux Application Developer
"One of my most productive days was throwing away 1000 lines of code."
- Ken Thompson.
-
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