Re: [PATCH] null_blk: Register as a LightNVM device

From: Jens Axboe
Date: Wed Nov 11 2015 - 16:27:42 EST

On 11/11/2015 03:06 AM, Matias BjÃrling 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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