[PATCH] quota: code cleanup for hash bits calculation

[PATCH] quota: code cleanup for hash bits calculation

[Chengguang Xu]

Code cleanup for hash bits calculation by
calling rounddown_pow_of_two() and ilog2()

Signed-off-by: Chengguang Xu <cgxu519@zoho.com.cn>
---
 fs/quota/dquot.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index 6e826b454082..679dd3b5db70 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -2983,13 +2983,9 @@ static int __init dquot_init(void)
 
 	/* Find power-of-two hlist_heads which can fit into allocation */
 	nr_hash = (1UL << order) * PAGE_SIZE / sizeof(struct hlist_head);
-	dq_hash_bits = 0;
-	do {
-		dq_hash_bits++;
-	} while (nr_hash >> dq_hash_bits);
-	dq_hash_bits--;
+	nr_hash = rounddown_pow_of_two(nr_hash);
+	dq_hash_bits = ilog2(nr_hash);
 
-	nr_hash = 1UL << dq_hash_bits;
 	dq_hash_mask = nr_hash - 1;
 	for (i = 0; i < nr_hash; i++)
 		INIT_HLIST_HEAD(dquot_hash + i);
-- 
2.21.0

Re: [PATCH] quota: code cleanup for hash bits calculation

[Jan Kara]

On Sat 21-09-19 09:56:28, Chengguang Xu wrote:
> Code cleanup for hash bits calculation by
> calling rounddown_pow_of_two() and ilog2()
> 
> Signed-off-by: Chengguang Xu <cgxu519@zoho.com.cn>

Thanks for the patch! One comment below:

> diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
> index 6e826b454082..679dd3b5db70 100644
> --- a/fs/quota/dquot.c
> +++ b/fs/quota/dquot.c
> @@ -2983,13 +2983,9 @@ static int __init dquot_init(void)
>  
>  	/* Find power-of-two hlist_heads which can fit into allocation */
>  	nr_hash = (1UL << order) * PAGE_SIZE / sizeof(struct hlist_head);
> -	dq_hash_bits = 0;
> -	do {
> -		dq_hash_bits++;
> -	} while (nr_hash >> dq_hash_bits);
> -	dq_hash_bits--;
> +	nr_hash = rounddown_pow_of_two(nr_hash);
> +	dq_hash_bits = ilog2(nr_hash);
>  
> -	nr_hash = 1UL << dq_hash_bits;

Why not just:
	dq_hash_bits = ilog2(nr_hash);
	nr_hash = 1UL << dq_hash_bits;

That way we need to compute fls() only once...

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH] quota: code cleanup for hash bits calculation

[admin]

 ---- 在 星期一, 2019-09-23 18:02:53 Jan Kara <jack@suse.cz> 撰写 ----
 > On Sat 21-09-19 09:56:28, Chengguang Xu wrote:
 > > Code cleanup for hash bits calculation by
 > > calling rounddown_pow_of_two() and ilog2()
 > > 
 > > Signed-off-by: Chengguang Xu <cgxu519@zoho.com.cn>
 > 
 > Thanks for the patch! One comment below:
 > 
 > > diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
 > > index 6e826b454082..679dd3b5db70 100644
 > > --- a/fs/quota/dquot.c
 > > +++ b/fs/quota/dquot.c
 > > @@ -2983,13 +2983,9 @@ static int __init dquot_init(void)
 > >  
 > >      /* Find power-of-two hlist_heads which can fit into allocation */
 > >      nr_hash = (1UL << order) * PAGE_SIZE / sizeof(struct hlist_head);
 > > -    dq_hash_bits = 0;
 > > -    do {
 > > -        dq_hash_bits++;
 > > -    } while (nr_hash >> dq_hash_bits);
 > > -    dq_hash_bits--;
 > > +    nr_hash = rounddown_pow_of_two(nr_hash);
 > > +    dq_hash_bits = ilog2(nr_hash);
 > >  
 > > -    nr_hash = 1UL << dq_hash_bits;
 > 
 > Why not just:
 >     dq_hash_bits = ilog2(nr_hash);
 >     nr_hash = 1UL << dq_hash_bits;
 > 
 > That way we need to compute fls() only once...
 
Yeah, you are right, I'll update in v2.

Thanks,
Chengguang