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

[Jens Axboe <axboe@kernel.dk>]

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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


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diff --git a/drivers/block/null_blk.c b/drivers/block/null_blk.c
index 1efaef6e54e9..31d5debc020e 100644
--- a/drivers/block/null_blk.c
+++ b/drivers/block/null_blk.c
@@ -446,8 +446,6 @@ static void null_del_dev(struct nullb *nullb)
 
 #ifdef CONFIG_NVM
 
-static struct kmem_cache *ppa_cache;
-
 static void null_lnvm_end_io(struct request *rq, int error)
 {
 	struct nvm_rq *rqd = rq->end_io_data;
@@ -523,13 +521,7 @@ 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);
+	virtmem_pool = mempool_create_page_pool(64, 0);
 	if (!virtmem_pool) {
 		pr_err("null_nvm: Unable to create virtual memory pool\n");
 		return NULL;
@@ -540,10 +532,8 @@ static void *null_lnvm_create_dma_pool(struct request_queue *q, char *name)
 
 static void null_lnvm_destroy_dma_pool(void *pool)
 {
-	mempool_t *virtmem_pool = pool;
+	mempool_destroy(pool);
 
-	mempool_destroy(virtmem_pool);
-}
 
 static void *null_lnvm_dev_dma_alloc(struct request_queue *q, void *pool,
 				gfp_t mem_flags, dma_addr_t *dma_handler)