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Subject: Re: [PATCH] lightnvm: pblk: remove unnecessary bio_get/put
To:     =?UTF-8?Q?Javier_Gonz=c3=a1lez?= <javier@javigon.com>,
        Jens Axboe <axboe@kernel.dk>
Cc:     linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        =?UTF-8?Q?Javier_Gonz=c3=a1lez?= <javier@cnexlabs.com>
References: <1527854506-8708-1-git-send-email-javier@cnexlabs.com>
 <1527854506-8708-2-git-send-email-javier@cnexlabs.com>
From:   =?UTF-8?Q?Matias_Bj=c3=b8rling?= <mb@lightnvm.io>
Message-ID: <f1579a62-0e85-b58d-ca33-a9635dd0ebaa@lightnvm.io>
Date:   Fri, 1 Jun 2018 14:05:14 +0200
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On 06/01/2018 02:01 PM, Javier González wrote:
> In the read path, pblk gets a reference to the incoming bio and puts it
> after ending the bio. Though this behavior is correct, it is unnecessary
> since pblk is the one putting the bio, therefore, it cannot disappear
> underneath it.
> 
> Removing this reference, allows to clean up rqd->bio and avoids pointer
> bouncing for the different read paths. Now, the incoming bio always
> resides in the read context and pblk's internal bios (if any) reside in
> rqd->bio.
> 
> Signed-off-by: Javier González <javier@cnexlabs.com>
> ---
>   drivers/lightnvm/pblk-read.c | 65 +++++++++++++++++++-------------------------
>   1 file changed, 28 insertions(+), 37 deletions(-)
> 
> diff --git a/drivers/lightnvm/pblk-read.c b/drivers/lightnvm/pblk-read.c
> index fa7b60f852d9..38360de23d4e 100644
> --- a/drivers/lightnvm/pblk-read.c
> +++ b/drivers/lightnvm/pblk-read.c
> @@ -39,10 +39,10 @@ static int pblk_read_from_cache(struct pblk *pblk, struct bio *bio,
>   }
>   
>   static void pblk_read_ppalist_rq(struct pblk *pblk, struct nvm_rq *rqd,
> -				 sector_t blba, unsigned long *read_bitmap)
> +				 struct bio *bio, sector_t blba,
> +				 unsigned long *read_bitmap)
>   {
>   	struct pblk_sec_meta *meta_list = rqd->meta_list;
> -	struct bio *bio = rqd->bio;
>   	struct ppa_addr ppas[PBLK_MAX_REQ_ADDRS];
>   	int nr_secs = rqd->nr_ppas;
>   	bool advanced_bio = false;
> @@ -189,7 +189,6 @@ static void pblk_end_user_read(struct bio *bio)
>   	WARN_ONCE(bio->bi_status, "pblk: corrupted read bio\n");
>   #endif
>   	bio_endio(bio);
> -	bio_put(bio);
>   }
>   
>   static void __pblk_end_io_read(struct pblk *pblk, struct nvm_rq *rqd,
> @@ -197,23 +196,18 @@ static void __pblk_end_io_read(struct pblk *pblk, struct nvm_rq *rqd,
>   {
>   	struct nvm_tgt_dev *dev = pblk->dev;
>   	struct pblk_g_ctx *r_ctx = nvm_rq_to_pdu(rqd);
> -	struct bio *bio = rqd->bio;
> +	struct bio *int_bio = rqd->bio;
>   	unsigned long start_time = r_ctx->start_time;
>   
>   	generic_end_io_acct(dev->q, READ, &pblk->disk->part0, start_time);
>   
>   	if (rqd->error)
>   		pblk_log_read_err(pblk, rqd);
> -#ifdef CONFIG_NVM_DEBUG
> -	else
> -		WARN_ONCE(bio->bi_status, "pblk: corrupted read error\n");
> -#endif
>   
>   	pblk_read_check_seq(pblk, rqd, r_ctx->lba);
>   
> -	bio_put(bio);
> -	if (r_ctx->private)
> -		pblk_end_user_read((struct bio *)r_ctx->private);
> +	if (int_bio)
> +		bio_put(int_bio);
>   
>   	if (put_line)
>   		pblk_read_put_rqd_kref(pblk, rqd);
> @@ -230,16 +224,19 @@ static void __pblk_end_io_read(struct pblk *pblk, struct nvm_rq *rqd,
>   static void pblk_end_io_read(struct nvm_rq *rqd)
>   {
>   	struct pblk *pblk = rqd->private;
> +	struct pblk_g_ctx *r_ctx = nvm_rq_to_pdu(rqd);
> +	struct bio *bio = (struct bio *)r_ctx->private;
>   
> +	pblk_end_user_read(bio);
>   	__pblk_end_io_read(pblk, rqd, true);
>   }
>   
> -static int pblk_partial_read_bio(struct pblk *pblk, struct nvm_rq *rqd,
> -				 unsigned int bio_init_idx,
> -				 unsigned long *read_bitmap)
> +static int pblk_partial_read(struct pblk *pblk, struct nvm_rq *rqd,
> +			     struct bio *orig_bio, unsigned int bio_init_idx,
> +			     unsigned long *read_bitmap)
>   {
> -	struct bio *new_bio, *bio = rqd->bio;
>   	struct pblk_sec_meta *meta_list = rqd->meta_list;
> +	struct bio *new_bio;
>   	struct bio_vec src_bv, dst_bv;
>   	void *ppa_ptr = NULL;
>   	void *src_p, *dst_p;
> @@ -256,11 +253,11 @@ static int pblk_partial_read_bio(struct pblk *pblk, struct nvm_rq *rqd,
>   	new_bio = bio_alloc(GFP_KERNEL, nr_holes);
>   
>   	if (pblk_bio_add_pages(pblk, new_bio, GFP_KERNEL, nr_holes))
> -		goto err_add_pages;
> +		goto fail_add_pages;
>   
>   	if (nr_holes != new_bio->bi_vcnt) {
>   		pr_err("pblk: malformed bio\n");
> -		goto err;
> +		goto fail;
>   	}
>   
>   	for (i = 0; i < nr_secs; i++)
> @@ -283,7 +280,7 @@ static int pblk_partial_read_bio(struct pblk *pblk, struct nvm_rq *rqd,
>   	if (ret) {
>   		bio_put(rqd->bio);
>   		pr_err("pblk: sync read IO submission failed\n");
> -		goto err;
> +		goto fail;
>   	}
>   
>   	if (rqd->error) {
> @@ -319,7 +316,7 @@ static int pblk_partial_read_bio(struct pblk *pblk, struct nvm_rq *rqd,
>   		meta_list[hole].lba = lba_list_media[i];
>   
>   		src_bv = new_bio->bi_io_vec[i++];
> -		dst_bv = bio->bi_io_vec[bio_init_idx + hole];
> +		dst_bv = orig_bio->bi_io_vec[bio_init_idx + hole];
>   
>   		src_p = kmap_atomic(src_bv.bv_page);
>   		dst_p = kmap_atomic(dst_bv.bv_page);
> @@ -338,28 +335,26 @@ static int pblk_partial_read_bio(struct pblk *pblk, struct nvm_rq *rqd,
>   
>   	bio_put(new_bio);
>   
> -	/* Complete the original bio and associated request */
> -	bio_endio(bio);
> -	rqd->bio = bio;
> +	/* restore original request */
> +	rqd->bio = NULL;
>   	rqd->nr_ppas = nr_secs;
>   
>   	__pblk_end_io_read(pblk, rqd, false);
> -	return NVM_IO_OK;
> +	return NVM_IO_DONE;
>   
> -err:
> +fail:
>   	/* Free allocated pages in new bio */
>   	pblk_bio_free_pages(pblk, new_bio, 0, new_bio->bi_vcnt);
> -err_add_pages:
> +fail_add_pages:
>   	pr_err("pblk: failed to perform partial read\n");
>   	__pblk_end_io_read(pblk, rqd, false);
>   	return NVM_IO_ERR;
>   }
>   
> -static void pblk_read_rq(struct pblk *pblk, struct nvm_rq *rqd,
> +static void pblk_read_rq(struct pblk *pblk, struct nvm_rq *rqd, struct bio *bio,
>   			 sector_t lba, unsigned long *read_bitmap)
>   {
>   	struct pblk_sec_meta *meta_list = rqd->meta_list;
> -	struct bio *bio = rqd->bio;
>   	struct ppa_addr ppa;
>   
>   	pblk_lookup_l2p_seq(pblk, &ppa, lba, 1);
> @@ -423,14 +418,15 @@ int pblk_submit_read(struct pblk *pblk, struct bio *bio)
>   	rqd = pblk_alloc_rqd(pblk, PBLK_READ);
>   
>   	rqd->opcode = NVM_OP_PREAD;
> -	rqd->bio = bio;
>   	rqd->nr_ppas = nr_secs;
> +	rqd->bio = NULL; /* cloned bio if needed */
>   	rqd->private = pblk;
>   	rqd->end_io = pblk_end_io_read;
>   
>   	r_ctx = nvm_rq_to_pdu(rqd);
>   	r_ctx->start_time = jiffies;
>   	r_ctx->lba = blba;
> +	r_ctx->private = bio; /* original bio */
>   
>   	/* Save the index for this bio's start. This is needed in case
>   	 * we need to fill a partial read.
> @@ -448,17 +444,15 @@ int pblk_submit_read(struct pblk *pblk, struct bio *bio)
>   		rqd->ppa_list = rqd->meta_list + pblk_dma_meta_size;
>   		rqd->dma_ppa_list = rqd->dma_meta_list + pblk_dma_meta_size;
>   
> -		pblk_read_ppalist_rq(pblk, rqd, blba, &read_bitmap);
> +		pblk_read_ppalist_rq(pblk, rqd, bio, blba, &read_bitmap);
>   	} else {
> -		pblk_read_rq(pblk, rqd, blba, &read_bitmap);
> +		pblk_read_rq(pblk, rqd, bio, blba, &read_bitmap);
>   	}
>   
> -	bio_get(bio);
>   	if (bitmap_full(&read_bitmap, nr_secs)) {
> -		bio_endio(bio);
>   		atomic_inc(&pblk->inflight_io);
>   		__pblk_end_io_read(pblk, rqd, false);
> -		return NVM_IO_OK;
> +		return NVM_IO_DONE;
>   	}
>   
>   	/* All sectors are to be read from the device */
> @@ -473,13 +467,10 @@ int pblk_submit_read(struct pblk *pblk, struct bio *bio)
>   		}
>   
>   		rqd->bio = int_bio;
> -		r_ctx->private = bio;
>   
>   		if (pblk_submit_io(pblk, rqd)) {
>   			pr_err("pblk: read IO submission failed\n");
>   			ret = NVM_IO_ERR;
> -			if (int_bio)
> -				bio_put(int_bio);
>   			goto fail_end_io;
>   		}
>   
> @@ -489,7 +480,7 @@ int pblk_submit_read(struct pblk *pblk, struct bio *bio)
>   	/* The read bio request could be partially filled by the write buffer,
>   	 * but there are some holes that need to be read from the drive.
>   	 */
> -	return pblk_partial_read_bio(pblk, rqd, bio_init_idx, &read_bitmap);
> +	return pblk_partial_read(pblk, rqd, bio, bio_init_idx, &read_bitmap);
>   
>   fail_rqd_free:
>   	pblk_free_rqd(pblk, rqd, PBLK_READ);
> 

Hi Jens,

Would you please pick this up as well?

Signed-off-by: Matias Bjørling <mb@lightnvm.io>