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[PATCH v1 1/5] block: introduce bio_clone_bioset_partial()

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  [PATCH v1 1/5] block: introduce bio_clone_bioset_partial() Ming Lei <tom.leiming@gmail.com> - 2017-02-10 12:00 +0100
    Re: [PATCH v1 1/5] block: introduce bio_clone_bioset_partial() Christoph Hellwig <hch@infradead.org> - 2017-02-13 14:50 +0100
      Re: [PATCH v1 1/5] block: introduce bio_clone_bioset_partial() Ming Lei <tom.leiming@gmail.com> - 2017-02-14 02:10 +0100
        Re: [PATCH v1 1/5] block: introduce bio_clone_bioset_partial() Christoph Hellwig <hch@infradead.org> - 2017-02-14 17:10 +0100
          Re: [PATCH v1 1/5] block: introduce bio_clone_bioset_partial() Ming Lei <tom.leiming@gmail.com> - 2017-02-15 03:30 +0100

#1578382 — [PATCH v1 1/5] block: introduce bio_clone_bioset_partial()

md still need bio clone(not the fast version) for behind write,
and it is more efficient to use bio_clone_bioset_partial().

The idea is simple and just copy the bvecs range specified from
parameters.

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
---
 block/bio.c         | 61 +++++++++++++++++++++++++++++++++++++++++------------
 include/linux/bio.h | 11 ++++++++--
 2 files changed, 57 insertions(+), 15 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 4b564d0c3e29..5eec5e08417f 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -625,21 +625,20 @@ struct bio *bio_clone_fast(struct bio *bio, gfp_t gfp_mask, struct bio_set *bs)
 }
 EXPORT_SYMBOL(bio_clone_fast);
 
-/**
- * 	bio_clone_bioset - clone a bio
- * 	@bio_src: bio to clone
- *	@gfp_mask: allocation priority
- *	@bs: bio_set to allocate from
- *
- *	Clone bio. Caller will own the returned bio, but not the actual data it
- *	points to. Reference count of returned bio will be one.
- */
-struct bio *bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
-			     struct bio_set *bs)
+static struct bio *__bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
+				      struct bio_set *bs, int offset,
+				      int size)
 {
 	struct bvec_iter iter;
 	struct bio_vec bv;
 	struct bio *bio;
+	struct bvec_iter iter_src = bio_src->bi_iter;
+
+	/* for supporting partial clone */
+	if (offset || size != bio_src->bi_iter.bi_size) {
+		bio_advance_iter(bio_src, &iter_src, offset);
+		iter_src.bi_size = size;
+	}
 
 	/*
 	 * Pre immutable biovecs, __bio_clone() used to just do a memcpy from
@@ -663,7 +662,8 @@ struct bio *bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
 	 *    __bio_clone_fast() anyways.
 	 */
 
-	bio = bio_alloc_bioset(gfp_mask, bio_segments(bio_src), bs);
+	bio = bio_alloc_bioset(gfp_mask, __bio_segments(bio_src,
+			       &iter_src), bs);
 	if (!bio)
 		return NULL;
 	bio->bi_bdev		= bio_src->bi_bdev;
@@ -680,7 +680,7 @@ struct bio *bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
 		bio->bi_io_vec[bio->bi_vcnt++] = bio_src->bi_io_vec[0];
 		break;
 	default:
-		bio_for_each_segment(bv, bio_src, iter)
+		__bio_for_each_segment(bv, bio_src, iter, iter_src)
 			bio->bi_io_vec[bio->bi_vcnt++] = bv;
 		break;
 	}
@@ -699,9 +699,44 @@ struct bio *bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
 
 	return bio;
 }
+
+/**
+ * 	bio_clone_bioset - clone a bio
+ * 	@bio_src: bio to clone
+ *	@gfp_mask: allocation priority
+ *	@bs: bio_set to allocate from
+ *
+ *	Clone bio. Caller will own the returned bio, but not the actual data it
+ *	points to. Reference count of returned bio will be one.
+ */
+struct bio *bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
+			     struct bio_set *bs)
+{
+	return __bio_clone_bioset(bio_src, gfp_mask, bs, 0,
+				  bio_src->bi_iter.bi_size);
+}
 EXPORT_SYMBOL(bio_clone_bioset);
 
 /**
+ * 	bio_clone_bioset_partial - clone a partial bio
+ * 	@bio_src: bio to clone
+ *	@gfp_mask: allocation priority
+ *	@bs: bio_set to allocate from
+ *	@offset: cloned starting from the offset
+ *	@size: size for the cloned bio
+ *
+ *	Clone bio. Caller will own the returned bio, but not the actual data it
+ *	points to. Reference count of returned bio will be one.
+ */
+struct bio *bio_clone_bioset_partial(struct bio *bio_src, gfp_t gfp_mask,
+				     struct bio_set *bs, int offset,
+				     int size)
+{
+	return __bio_clone_bioset(bio_src, gfp_mask, bs, offset, size);
+}
+EXPORT_SYMBOL(bio_clone_bioset_partial);
+
+/**
  *	bio_add_pc_page	-	attempt to add page to bio
  *	@q: the target queue
  *	@bio: destination bio
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 7cf8a6c70a3f..8e521194f6fc 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -183,7 +183,7 @@ static inline void bio_advance_iter(struct bio *bio, struct bvec_iter *iter,
 
 #define bio_iter_last(bvec, iter) ((iter).bi_size == (bvec).bv_len)
 
-static inline unsigned bio_segments(struct bio *bio)
+static inline unsigned __bio_segments(struct bio *bio, struct bvec_iter *bvec)
 {
 	unsigned segs = 0;
 	struct bio_vec bv;
@@ -205,12 +205,17 @@ static inline unsigned bio_segments(struct bio *bio)
 		break;
 	}
 
-	bio_for_each_segment(bv, bio, iter)
+	__bio_for_each_segment(bv, bio, iter, *bvec)
 		segs++;
 
 	return segs;
 }
 
+static inline unsigned bio_segments(struct bio *bio)
+{
+	return __bio_segments(bio, &bio->bi_iter);
+}
+
 /*
  * get a reference to a bio, so it won't disappear. the intended use is
  * something like:
@@ -384,6 +389,8 @@ extern void bio_put(struct bio *);
 extern void __bio_clone_fast(struct bio *, struct bio *);
 extern struct bio *bio_clone_fast(struct bio *, gfp_t, struct bio_set *);
 extern struct bio *bio_clone_bioset(struct bio *, gfp_t, struct bio_set *bs);
+extern struct bio *bio_clone_bioset_partial(struct bio *, gfp_t,
+					    struct bio_set *, int, int);
 
 extern struct bio_set *fs_bio_set;
 
-- 
2.7.4

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#1579792

On Fri, Feb 10, 2017 at 06:56:13PM +0800, Ming Lei wrote:
> md still need bio clone(not the fast version) for behind write,
> and it is more efficient to use bio_clone_bioset_partial().
> 
> The idea is simple and just copy the bvecs range specified from
> parameters.

Given how few users bio_clone_bioset has I wonder if we shouldn't
simply add the two new arguments to it instead of adding another
indirection.

Otherwise looks fine:

Reviewed-by: Christoph Hellwig <hch@lst.de>

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#1580176

On Mon, Feb 13, 2017 at 9:46 PM, Christoph Hellwig <hch@infradead.org> wrote:
> On Fri, Feb 10, 2017 at 06:56:13PM +0800, Ming Lei wrote:
>> md still need bio clone(not the fast version) for behind write,
>> and it is more efficient to use bio_clone_bioset_partial().
>>
>> The idea is simple and just copy the bvecs range specified from
>> parameters.
>
> Given how few users bio_clone_bioset has I wonder if we shouldn't
> simply add the two new arguments to it instead of adding another
> indirection.

For md write-behind, looks we have to provide the two arguments,
could you explain a bit how we can do that by adding another indirection?

>
> Otherwise looks fine:
>
> Reviewed-by: Christoph Hellwig <hch@lst.de>

Thanks!

-- 
Ming Lei

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#1580626

On Tue, Feb 14, 2017 at 09:04:26AM +0800, Ming Lei wrote:
> On Mon, Feb 13, 2017 at 9:46 PM, Christoph Hellwig <hch@infradead.org> wrote:
> > On Fri, Feb 10, 2017 at 06:56:13PM +0800, Ming Lei wrote:
> >> md still need bio clone(not the fast version) for behind write,
> >> and it is more efficient to use bio_clone_bioset_partial().
> >>
> >> The idea is simple and just copy the bvecs range specified from
> >> parameters.
> >
> > Given how few users bio_clone_bioset has I wonder if we shouldn't
> > simply add the two new arguments to it instead of adding another
> > indirection.
> 
> For md write-behind, looks we have to provide the two arguments,
> could you explain a bit how we can do that by adding another indirection?

I meant to just pass the additional arguments that 
bio_clone_bioset_partial has to bio_clone_bioset.

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#1581002

On Wed, Feb 15, 2017 at 12:01 AM, Christoph Hellwig <hch@infradead.org> wrote:
> On Tue, Feb 14, 2017 at 09:04:26AM +0800, Ming Lei wrote:
>> On Mon, Feb 13, 2017 at 9:46 PM, Christoph Hellwig <hch@infradead.org> wrote:
>> > On Fri, Feb 10, 2017 at 06:56:13PM +0800, Ming Lei wrote:
>> >> md still need bio clone(not the fast version) for behind write,
>> >> and it is more efficient to use bio_clone_bioset_partial().
>> >>
>> >> The idea is simple and just copy the bvecs range specified from
>> >> parameters.
>> >
>> > Given how few users bio_clone_bioset has I wonder if we shouldn't
>> > simply add the two new arguments to it instead of adding another
>> > indirection.
>>
>> For md write-behind, looks we have to provide the two arguments,
>> could you explain a bit how we can do that by adding another indirection?
>
> I meant to just pass the additional arguments that
> bio_clone_bioset_partial has to bio_clone_bioset.

That may cause more changes(fs, ...) into this patchset, so I suggest to
do that in another patchset, especially after we confirmed current
users of bio_clone is absolutely necessary, and I will check if other bio_clone
can be converted to fast clone.


Thanks,
Ming Lei

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