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Old 08-06-2012, 10:08 PM
Kent Overstreet
 
Default block: Add bio_reset()

Reusing bios is something that's been highly frowned upon in the past,
but driver code keeps doing it anyways. If it's going to happen anyways,
we should provide a generic method.

This'll help with getting rid of bi_destructor - drivers/block/pktcdvd.c
was open coding it, by doing a bio_init() and resetting bi_destructor.

v5: Add a define BIO_RESET_BITS, to be very explicit about what parts of
bio->bi_flags are saved.

Signed-off-by: Kent Overstreet <koverstreet@google.com>
Change-Id: I4eb2975bd678d3be811d5423d0620b08020be9ff
---
fs/bio.c | 9 +++++++++
include/linux/bio.h | 1 +
include/linux/blk_types.h | 9 +++++++++
3 files changed, 19 insertions(+), 0 deletions(-)

diff --git a/fs/bio.c b/fs/bio.c
index 1c6c8b7..c7f3442 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -261,6 +261,15 @@ void bio_init(struct bio *bio)
}
EXPORT_SYMBOL(bio_init);

+void bio_reset(struct bio *bio)
+{
+ unsigned long flags = bio->bi_flags & (~0UL << BIO_RESET_BITS);
+
+ memset(bio, 0, BIO_RESET_BYTES);
+ bio->bi_flags = flags|(1 << BIO_UPTODATE);
+}
+EXPORT_SYMBOL(bio_reset);
+
/**
* bio_alloc_bioset - allocate a bio for I/O
* @gfp_mask: the GFP_ mask given to the slab allocator
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 2643589..ba60319 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -226,6 +226,7 @@ extern void __bio_clone(struct bio *, struct bio *);
extern struct bio *bio_clone(struct bio *, gfp_t);

extern void bio_init(struct bio *);
+extern void bio_reset(struct bio *);

extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int);
extern int bio_add_pc_page(struct request_queue *, struct bio *, struct page *,
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 293547e..401c573 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -59,6 +59,10 @@ struct bio {
unsigned int bi_seg_front_size;
unsigned int bi_seg_back_size;

+ /*
+ * Everything starting with bi_max_vecs will be preserved by bio_reset()
+ */
+
unsigned int bi_max_vecs; /* max bvl_vecs we can hold */

atomic_t bi_cnt; /* pin count */
@@ -93,6 +97,8 @@ struct bio {
struct bio_vec bi_inline_vecs[0];
};

+#define BIO_RESET_BYTES offsetof(struct bio, bi_max_vecs)
+
/*
* bio flags
*/
@@ -108,6 +114,9 @@ struct bio {
#define BIO_FS_INTEGRITY 9 /* fs owns integrity data, not block layer */
#define BIO_QUIET 10 /* Make BIO Quiet */
#define BIO_MAPPED_INTEGRITY 11/* integrity metadata has been remapped */
+
+#define BIO_RESET_BITS 12 /* Flags starting here get preserved by bio_reset() */
+
#define bio_flagged(bio, flag) ((bio)->bi_flags & (1 << (flag)))

/*
--
1.7.7.3

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Old 08-08-2012, 10:11 PM
Tejun Heo
 
Default block: Add bio_reset()

Hello,

On Mon, Aug 06, 2012 at 03:08:32PM -0700, Kent Overstreet wrote:
> Reusing bios is something that's been highly frowned upon in the past,
> but driver code keeps doing it anyways. If it's going to happen anyways,
> we should provide a generic method.
>
> This'll help with getting rid of bi_destructor - drivers/block/pktcdvd.c
> was open coding it, by doing a bio_init() and resetting bi_destructor.
>
> v5: Add a define BIO_RESET_BITS, to be very explicit about what parts of
> bio->bi_flags are saved.
>
> Signed-off-by: Kent Overstreet <koverstreet@google.com>
> Change-Id: I4eb2975bd678d3be811d5423d0620b08020be9ff

Please drop Change-Id. Die gerrit die.

> +void bio_reset(struct bio *bio)
> +{
> + unsigned long flags = bio->bi_flags & (~0UL << BIO_RESET_BITS);

How many flags are we talking about? If there aren't too many, I'd
prefer explicit BIO_FLAGS_PRESERVED or whatever.

Thanks.

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Old 08-09-2012, 12:07 AM
Kent Overstreet
 
Default block: Add bio_reset()

On Wed, Aug 08, 2012 at 03:11:29PM -0700, Tejun Heo wrote:
> Hello,
>
> On Mon, Aug 06, 2012 at 03:08:32PM -0700, Kent Overstreet wrote:
> > Reusing bios is something that's been highly frowned upon in the past,
> > but driver code keeps doing it anyways. If it's going to happen anyways,
> > we should provide a generic method.
> >
> > This'll help with getting rid of bi_destructor - drivers/block/pktcdvd.c
> > was open coding it, by doing a bio_init() and resetting bi_destructor.
> >
> > v5: Add a define BIO_RESET_BITS, to be very explicit about what parts of
> > bio->bi_flags are saved.
> >
> > Signed-off-by: Kent Overstreet <koverstreet@google.com>
> > Change-Id: I4eb2975bd678d3be811d5423d0620b08020be9ff
>
> Please drop Change-Id. Die gerrit die.

Bah, missed that one.

> > +void bio_reset(struct bio *bio)
> > +{
> > + unsigned long flags = bio->bi_flags & (~0UL << BIO_RESET_BITS);
>
> How many flags are we talking about? If there aren't too many, I'd
> prefer explicit BIO_FLAGS_PRESERVED or whatever.

It mostly isn't actual flags that are preserved - the high bits of the
flags are used for indicating what slab the bvec was allocated from, and
that's the main thing that has to be preserved.

So that's why I went with defining the things that are reset instead of
the things that are preserved.

I would prefer if bitfields were used for at least BIO_POOL_IDX, but the
problem is flags is used as an atomic bit vector for BIO_UPTODATE.

But flags isn't treated as an atomic bit vector elsewhere -
bio_flagged() doesn't use test_bit(), and flags are set/cleared with
atomic bit operations in some places but not in others (probably _most_
of them are technically safe, but... ick).

>
> Thanks.
>
> --
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Old 08-09-2012, 06:00 AM
Tejun Heo
 
Default block: Add bio_reset()

Hello,

On Wed, Aug 08, 2012 at 05:07:11PM -0700, Kent Overstreet wrote:
> > > +void bio_reset(struct bio *bio)
> > > +{
> > > + unsigned long flags = bio->bi_flags & (~0UL << BIO_RESET_BITS);
> >
> > How many flags are we talking about? If there aren't too many, I'd
> > prefer explicit BIO_FLAGS_PRESERVED or whatever.
>
> It mostly isn't actual flags that are preserved - the high bits of the
> flags are used for indicating what slab the bvec was allocated from, and
> that's the main thing that has to be preserved.
>
> So that's why I went with defining the things that are reset instead of
> the things that are preserved.
>
> I would prefer if bitfields were used for at least BIO_POOL_IDX, but the
> problem is flags is used as an atomic bit vector for BIO_UPTODATE.
>
> But flags isn't treated as an atomic bit vector elsewhere -
> bio_flagged() doesn't use test_bit(), and flags are set/cleared with

Not using test_bit() may not be necessarily wrong.

> atomic bit operations in some places but not in others (probably _most_
> of them are technically safe, but... ick).

Mixing atomic and non-atomic modifications is almost always wrong tho.

Anyways, understood. Can you *please* put some comment what bits are
being preserved across reset then? Things like this aren't obvious at
all and need ample explanation.

Thanks.

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Old 08-09-2012, 06:06 AM
Kent Overstreet
 
Default block: Add bio_reset()

On Wed, Aug 08, 2012 at 11:00:19PM -0700, Tejun Heo wrote:
> Anyways, understood. Can you *please* put some comment what bits are
> being preserved across reset then? Things like this aren't obvious at
> all and need ample explanation.

I did, in the header:

#define BIO_RESET_BITS 12 /* Flags starting here get preserved by
bio_reset() */

Where the rest of the flags are defined, and near where BIO_RESET_BYTES
are defined.

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Old 08-09-2012, 06:30 AM
Tejun Heo
 
Default block: Add bio_reset()

Hello,

On Wed, Aug 8, 2012 at 11:06 PM, Kent Overstreet <koverstreet@google.com> wrote:
> On Wed, Aug 08, 2012 at 11:00:19PM -0700, Tejun Heo wrote:
>> Anyways, understood. Can you *please* put some comment what bits are
>> being preserved across reset then? Things like this aren't obvious at
>> all and need ample explanation.
>
> I did, in the header:
>
> #define BIO_RESET_BITS 12 /* Flags starting here get preserved by
> bio_reset() */
>
> Where the rest of the flags are defined, and near where BIO_RESET_BYTES
> are defined.

Yeah, I was hoping for the comment to note that the protected bits
include the pool index.

Thanks.

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Old 08-22-2012, 05:04 PM
Kent Overstreet
 
Default block: Add bio_reset()

Reusing bios is something that's been highly frowned upon in the past,
but driver code keeps doing it anyways. If it's going to happen anyways,
we should provide a generic method.

This'll help with getting rid of bi_destructor - drivers/block/pktcdvd.c
was open coding it, by doing a bio_init() and resetting bi_destructor.

v5: Add a define BIO_RESET_BITS, to be very explicit about what parts of
bio->bi_flags are saved.
v6: Further commenting verbosity, per Tejun

Signed-off-by: Kent Overstreet <koverstreet@google.com>
CC: Jens Axboe <axboe@kernel.dk>
---
fs/bio.c | 9 +++++++++
include/linux/bio.h | 1 +
include/linux/blk_types.h | 13 +++++++++++++
3 files changed, 23 insertions(+)

diff --git a/fs/bio.c b/fs/bio.c
index 86e0534..81bdf4f 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -261,6 +261,15 @@ void bio_init(struct bio *bio)
}
EXPORT_SYMBOL(bio_init);

+void bio_reset(struct bio *bio)
+{
+ unsigned long flags = bio->bi_flags & (~0UL << BIO_RESET_BITS);
+
+ memset(bio, 0, BIO_RESET_BYTES);
+ bio->bi_flags = flags|(1 << BIO_UPTODATE);
+}
+EXPORT_SYMBOL(bio_reset);
+
/**
* bio_alloc_bioset - allocate a bio for I/O
* @gfp_mask: the GFP_ mask given to the slab allocator
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 2643589..ba60319 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -226,6 +226,7 @@ extern void __bio_clone(struct bio *, struct bio *);
extern struct bio *bio_clone(struct bio *, gfp_t);

extern void bio_init(struct bio *);
+extern void bio_reset(struct bio *);

extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int);
extern int bio_add_pc_page(struct request_queue *, struct bio *, struct page *,
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index af9dd9d..4fe4984 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -59,6 +59,10 @@ struct bio {
unsigned int bi_seg_front_size;
unsigned int bi_seg_back_size;

+ /*
+ * Everything starting with bi_max_vecs will be preserved by bio_reset()
+ */
+
unsigned int bi_max_vecs; /* max bvl_vecs we can hold */

atomic_t bi_cnt; /* pin count */
@@ -93,6 +97,8 @@ struct bio {
struct bio_vec bi_inline_vecs[0];
};

+#define BIO_RESET_BYTES offsetof(struct bio, bi_max_vecs)
+
/*
* bio flags
*/
@@ -108,6 +114,13 @@ struct bio {
#define BIO_FS_INTEGRITY 9 /* fs owns integrity data, not block layer */
#define BIO_QUIET 10 /* Make BIO Quiet */
#define BIO_MAPPED_INTEGRITY 11/* integrity metadata has been remapped */
+
+/*
+ * Flags starting here get preserved by bio_reset() - this includes
+ * BIO_POOL_IDX()
+ */
+#define BIO_RESET_BITS 12
+
#define bio_flagged(bio, flag) ((bio)->bi_flags & (1 << (flag)))

/*
--
1.7.12

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Old 08-22-2012, 06:34 PM
Tejun Heo
 
Default block: Add bio_reset()

On Wed, Aug 22, 2012 at 10:04:00AM -0700, Kent Overstreet wrote:
> Reusing bios is something that's been highly frowned upon in the past,
> but driver code keeps doing it anyways. If it's going to happen anyways,
> we should provide a generic method.
>
> This'll help with getting rid of bi_destructor - drivers/block/pktcdvd.c
> was open coding it, by doing a bio_init() and resetting bi_destructor.
>
> v5: Add a define BIO_RESET_BITS, to be very explicit about what parts of
> bio->bi_flags are saved.
> v6: Further commenting verbosity, per Tejun
>
> Signed-off-by: Kent Overstreet <koverstreet@google.com>
> CC: Jens Axboe <axboe@kernel.dk>

Given some users are converted later.

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

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Old 08-22-2012, 07:51 PM
Tejun Heo
 
Default block: Add bio_reset()

On Wed, Aug 22, 2012 at 11:34:26AM -0700, Tejun Heo wrote:
> On Wed, Aug 22, 2012 at 10:04:00AM -0700, Kent Overstreet wrote:
> > Reusing bios is something that's been highly frowned upon in the past,
> > but driver code keeps doing it anyways. If it's going to happen anyways,
> > we should provide a generic method.
> >
> > This'll help with getting rid of bi_destructor - drivers/block/pktcdvd.c
> > was open coding it, by doing a bio_init() and resetting bi_destructor.
> >
> > v5: Add a define BIO_RESET_BITS, to be very explicit about what parts of
> > bio->bi_flags are saved.
> > v6: Further commenting verbosity, per Tejun
> >
> > Signed-off-by: Kent Overstreet <koverstreet@google.com>
> > CC: Jens Axboe <axboe@kernel.dk>
>
> Given some users are converted later.
>
> Acked-by: Tejun Heo <tj@kernel.org>

Noticed it was a bit fuzzy which fields get reset and which aren't and
had a off-line discussion with Kent. The conclusion was that
bi_end_io and bi_private should be reset and bi_integrity should be
freed on bio_reset().

Thanks.

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Old 08-28-2012, 05:37 PM
Kent Overstreet
 
Default block: Add bio_reset()

Reusing bios is something that's been highly frowned upon in the past,
but driver code keeps doing it anyways. If it's going to happen anyways,
we should provide a generic method.

This'll help with getting rid of bi_destructor - drivers/block/pktcdvd.c
was open coding it, by doing a bio_init() and resetting bi_destructor.

v5: Add a define BIO_RESET_BITS, to be very explicit about what parts of
bio->bi_flags are saved.
v6: Further commenting verbosity, per Tejun

Signed-off-by: Kent Overstreet <koverstreet@google.com>
CC: Jens Axboe <axboe@kernel.dk>
Acked-by: Tejun Heo <tj@kernel.org>
---
fs/bio.c | 14 ++++++++++++++
include/linux/bio.h | 1 +
include/linux/blk_types.h | 21 +++++++++++++++++----
3 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/fs/bio.c b/fs/bio.c
index e017f7a..52da084 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -262,6 +262,20 @@ void bio_init(struct bio *bio)
}
EXPORT_SYMBOL(bio_init);

+void bio_reset(struct bio *bio)
+{
+ unsigned long flags = bio->bi_flags & (~0UL << BIO_RESET_BITS);
+
+ if (bio_integrity(bio))
+ bio_integrity_free(bio, bio->bi_pool);
+
+ bio_disassociate_task(bio);
+
+ memset(bio, 0, BIO_RESET_BYTES);
+ bio->bi_flags = flags|(1 << BIO_UPTODATE);
+}
+EXPORT_SYMBOL(bio_reset);
+
/**
* bio_alloc_bioset - allocate a bio for I/O
* @gfp_mask: the GFP_ mask given to the slab allocator
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 2643589..ba60319 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -226,6 +226,7 @@ extern void __bio_clone(struct bio *, struct bio *);
extern struct bio *bio_clone(struct bio *, gfp_t);

extern void bio_init(struct bio *);
+extern void bio_reset(struct bio *);

extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int);
extern int bio_add_pc_page(struct request_queue *, struct bio *, struct page *,
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index af9dd9d..691edd1 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -59,15 +59,19 @@ struct bio {
unsigned int bi_seg_front_size;
unsigned int bi_seg_back_size;

+ bio_end_io_t *bi_end_io;
+
+ void *bi_private;
+
+ /*
+ * Everything starting with bi_max_vecs will be preserved by bio_reset()
+ */
+
unsigned int bi_max_vecs; /* max bvl_vecs we can hold */

atomic_t bi_cnt; /* pin count */

struct bio_vec *bi_io_vec; /* the actual vec list */
-
- bio_end_io_t *bi_end_io;
-
- void *bi_private;
#ifdef CONFIG_BLK_CGROUP
/*
* Optional ioc and css associated with this bio. Put on bio
@@ -93,6 +97,8 @@ struct bio {
struct bio_vec bi_inline_vecs[0];
};

+#define BIO_RESET_BYTES offsetof(struct bio, bi_max_vecs)
+
/*
* bio flags
*/
@@ -108,6 +114,13 @@ struct bio {
#define BIO_FS_INTEGRITY 9 /* fs owns integrity data, not block layer */
#define BIO_QUIET 10 /* Make BIO Quiet */
#define BIO_MAPPED_INTEGRITY 11/* integrity metadata has been remapped */
+
+/*
+ * Flags starting here get preserved by bio_reset() - this includes
+ * BIO_POOL_IDX()
+ */
+#define BIO_RESET_BITS 12
+
#define bio_flagged(bio, flag) ((bio)->bi_flags & (1 << (flag)))

/*
--
1.7.12

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