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

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Date:	Wed, 11 Nov 2015 15:11:17 -0700
From:	Jens Axboe <axboe@...nel.dk>
To:	Matias Bjørling <m@...rling.me>,
	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 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.

-- 
Jens Axboe


View attachment "null-lightnvm" of type "text/plain" (1272 bytes)