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

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Date:	Wed, 11 Nov 2015 14:27:34 -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 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?

-- 
Jens Axboe

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