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

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Date:   Mon, 23 Sep 2019 21:36:04 +0800
From:   admin <cgxu519@...o.com.cn>
To:     "Jan Kara" <jack@...e.cz>
Cc:     "Jan Kara" <jack@...e.com>,
        "linux-kernel" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] quota: code cleanup for hash bits calculation

 ---- 在 星期一, 2019-09-23 18:02:53 Jan Kara <jack@...e.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@...o.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