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[PATCH v2 16/51] block: bounce: avoid direct access to bvec table

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  [PATCH v2 16/51] block: bounce: avoid direct access to bvec table Ming Lei <ming.lei@redhat.com> - 2017-06-26 14:20 +0200
    Re: [PATCH v2 16/51] block: bounce: avoid direct access to bvec table Matthew Wilcox <willy@infradead.org> - 2017-06-27 08:20 +0200
      Re: [PATCH v2 16/51] block: bounce: avoid direct access to bvec table Ming Lei <ming.lei@redhat.com> - 2017-06-27 09:40 +0200

#1674679 — [PATCH v2 16/51] block: bounce: avoid direct access to bvec table

We will support multipage bvecs in the future, so change to
iterator way for getting bv_page of bvec from original bio.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/bounce.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/block/bounce.c b/block/bounce.c
index 916ee9a9a216..4eea1b2d8618 100644
--- a/block/bounce.c
+++ b/block/bounce.c
@@ -135,21 +135,22 @@ static void copy_to_high_bio_irq(struct bio *to, struct bio *from)
 static void bounce_end_io(struct bio *bio, mempool_t *pool)
 {
 	struct bio *bio_orig = bio->bi_private;
-	struct bio_vec *bvec, *org_vec;
+	struct bio_vec *bvec, orig_vec;
 	int i;
-	int start = bio_orig->bi_iter.bi_idx;
+	struct bvec_iter orig_iter = bio_orig->bi_iter;
 
 	/*
 	 * free up bounce indirect pages used
 	 */
 	bio_for_each_segment_all(bvec, bio, i) {
-		org_vec = bio_orig->bi_io_vec + i + start;
-
-		if (bvec->bv_page == org_vec->bv_page)
-			continue;
+		orig_vec = bio_iter_iovec(bio_orig, orig_iter);
+		if (bvec->bv_page == orig_vec.bv_page)
+			goto next;
 
 		dec_zone_page_state(bvec->bv_page, NR_BOUNCE);
 		mempool_free(bvec->bv_page, pool);
+ next:
+		bio_advance_iter(bio_orig, &orig_iter, orig_vec.bv_len);
 	}
 
 	bio_orig->bi_status = bio->bi_status;
-- 
2.9.4

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#1675320

On Mon, Jun 26, 2017 at 08:09:59PM +0800, Ming Lei wrote:
>  	bio_for_each_segment_all(bvec, bio, i) {
> -		org_vec = bio_orig->bi_io_vec + i + start;
> -
> -		if (bvec->bv_page == org_vec->bv_page)
> -			continue;
> +		orig_vec = bio_iter_iovec(bio_orig, orig_iter);
> +		if (bvec->bv_page == orig_vec.bv_page)
> +			goto next;
>  
>  		dec_zone_page_state(bvec->bv_page, NR_BOUNCE);
>  		mempool_free(bvec->bv_page, pool);
> + next:
> +		bio_advance_iter(bio_orig, &orig_iter, orig_vec.bv_len);
>  	}
>  

I think this might be written more clearly as:

 	bio_for_each_segment_all(bvec, bio, i) {
		orig_vec = bio_iter_iovec(bio_orig, orig_iter);
		if (bvec->bv_page != orig_vec.bv_page) {
 			dec_zone_page_state(bvec->bv_page, NR_BOUNCE);
	 		mempool_free(bvec->bv_page, pool);
		}
		bio_advance_iter(bio_orig, &orig_iter, orig_vec.bv_len);
 	}

What do you think?

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#1675377

On Mon, Jun 26, 2017 at 11:12:11PM -0700, Matthew Wilcox wrote:
> On Mon, Jun 26, 2017 at 08:09:59PM +0800, Ming Lei wrote:
> >  	bio_for_each_segment_all(bvec, bio, i) {
> > -		org_vec = bio_orig->bi_io_vec + i + start;
> > -
> > -		if (bvec->bv_page == org_vec->bv_page)
> > -			continue;
> > +		orig_vec = bio_iter_iovec(bio_orig, orig_iter);
> > +		if (bvec->bv_page == orig_vec.bv_page)
> > +			goto next;
> >  
> >  		dec_zone_page_state(bvec->bv_page, NR_BOUNCE);
> >  		mempool_free(bvec->bv_page, pool);
> > + next:
> > +		bio_advance_iter(bio_orig, &orig_iter, orig_vec.bv_len);
> >  	}
> >  
> 
> I think this might be written more clearly as:
> 
>  	bio_for_each_segment_all(bvec, bio, i) {
> 		orig_vec = bio_iter_iovec(bio_orig, orig_iter);
> 		if (bvec->bv_page != orig_vec.bv_page) {
>  			dec_zone_page_state(bvec->bv_page, NR_BOUNCE);
> 	 		mempool_free(bvec->bv_page, pool);
> 		}
> 		bio_advance_iter(bio_orig, &orig_iter, orig_vec.bv_len);
>  	}
> 
> What do you think?

Yeah, looks the above code is more clean, will do it in V3.

thanks,
Ming

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