linux-kernel - Re: [PATCH] null_blk: Use bitmap

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Message-ID: <974640be-a87e-5a46-3dcc-ba8dbf79c9cf@opensource.wdc.com>
Date:   Thu, 6 Jan 2022 16:49:32 +0900
From:   Damien Le Moal <damien.lemoal@...nsource.wdc.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        axboe@...nel.dk, chaitanya.kulkarni@....com, damien.lemoal@....com,
        ming.lei@...hat.com, Johannes.Thumshirn@....com,
        shinichiro.kawasaki@....com, jiangguoqing@...inos.cn,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] null_blk: Use bitmap_zalloc() when applicable

On 1/6/22 16:44, Dan Carpenter wrote:
> On Thu, Dec 30, 2021 at 11:28:28AM +0900, Damien Le Moal wrote:
>>>  
>>> -	tag_size = ALIGN(nq->queue_depth, BITS_PER_LONG) / BITS_PER_LONG;
>>> -	nq->tag_map = kcalloc(tag_size, sizeof(unsigned long), GFP_KERNEL);
>>> +	nq->tag_map = bitmap_zalloc(nq->queue_depth, GFP_KERNEL);
>>>  	if (!nq->tag_map) {
>>>  		kfree(nq->cmds);
>>>  		return -ENOMEM;
>>
>> Before this patch, tag_size would always be a multiple of BITS_PER_LONG.
>> Using bitmap_zalloc(), that alignment goes away, but I think this is OK.
>>
> 
> It's still going to be a multiple of long.  Bitmaps are always stored
> in longs.

Yes, I understand that. I was referring to tag_size, which was rounded
before. But tag_size is only a local variable and not the actual queue
depth, which is not rounded. I got confused :)

> 
> regards,
> dan carpenter
> 


-- 
Damien Le Moal
Western Digital Research