linux-kernel - Re: [PATCH] null_blk: Register as a LightNVM device

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Date:	Thu, 12 Nov 2015 12:30:11 +0100
From:	Matias Bjørling <m@...rling.me>
To:	Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org
CC:	axboe@...com
Subject: Re: [PATCH] null_blk: Register as a LightNVM device

On 11/11/2015 11:11 PM, Jens Axboe wrote:
> On 11/11/2015 02:27 PM, Jens Axboe wrote:
>> On 11/11/2015 03:06 AM, Matias Bjørling wrote:
>>> Add support for registering as a LightNVM device. This allows us to
>>> evaluate the performance of the LightNVM library.
>>>
>>> In /drivers/Makefile, LightNVM is moved above block device drivers
>>> to make sure that the LightNVM media managers have been initialized
>>> before drivers under /drivers/block are initialized.
>>
>> Generally looks ok. One question:
>>
>>> +static void *null_lnvm_create_dma_pool(struct request_queue *q, char
>>> *name)
>>> +{
>>> +    mempool_t *virtmem_pool;
>>> +
>>> +    ppa_cache = kmem_cache_create(name, PAGE_SIZE, 0, 0, NULL);
>>> +    if (!ppa_cache) {
>>> +        pr_err("null_nvm: Unable to create kmem cache\n");
>>> +        return NULL;
>>> +    }
>>> +
>>> +    virtmem_pool = mempool_create_slab_pool(64, ppa_cache);
>>> +    if (!virtmem_pool) {
>>> +        pr_err("null_nvm: Unable to create virtual memory pool\n");
>>> +        return NULL;
>>> +    }
>>> +
>>> +    return virtmem_pool;
>>> +}
>>
>> Why create a slab cache if it's pages? Why not just have the mempool
>> alloc/free alloc single pages?
>
> Ala attached. Also fixes a leak of not freeing the ppa_cache slab cache.
> Did you try and load/reload the module? I'm thinking it would have crashed.
>

Good idea. I'll apply it. Thanks
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