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Go Back   Linux Archive > Redhat > Device-mapper Development

 
 
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Old 09-12-2011, 01:42 PM
Christoph Hellwig
 
Default block: refactor generic_make_request

Move all the checks performed on a bio into a new helper, and call it as
soon as bio is submitted even if it is a re-submission from ->make_request.

We explicitly mark the new helper as beeing non-inlined as the stack
usage for printing the block device name in the failure case is quite
high and this a patch where we have to be extremely conservative about
stack usage.

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

Index: linux-2.6/block/blk-core.c
================================================== =================
--- linux-2.6.orig/block/blk-core.c 2011-09-08 12:07:09.943065855 +0200
+++ linux-2.6/block/blk-core.c 2011-09-08 12:08:23.463277870 +0200
@@ -1412,31 +1412,8 @@ static inline int bio_check_eod(struct b
return 0;
}

-/**
- * generic_make_request - hand a buffer to its device driver for I/O
- * @bio: The bio describing the location in memory and on the device.
- *
- * generic_make_request() is used to make I/O requests of block
- * devices. It is passed a &struct bio, which describes the I/O that needs
- * to be done.
- *
- * generic_make_request() does not return any status. The
- * success/failure status of the request, along with notification of
- * completion, is delivered asynchronously through the bio->bi_end_io
- * function described (one day) else where.
- *
- * The caller of generic_make_request must make sure that bi_io_vec
- * are set to describe the memory buffer, and that bi_dev and bi_sector are
- * set to describe the device address, and the
- * bi_end_io and optionally bi_private are set to describe how
- * completion notification should be signaled.
- *
- * generic_make_request and the drivers it calls may use bi_next if this
- * bio happens to be merged with someone else, and may change bi_dev and
- * bi_sector for remaps as it sees fit. So the values of these fields
- * should NOT be depended on after the call to generic_make_request.
- */
-static inline void __generic_make_request(struct bio *bio)
+static noinline_for_stack bool
+generic_make_request_checks(struct bio *bio)
{
struct request_queue *q;
int nr_sectors = bio_sectors(bio);
@@ -1515,35 +1492,62 @@ static inline void __generic_make_reques

/* if bio = NULL, bio has been throttled and will be submitted later. */
if (!bio)
- return;
+ return false;
+
trace_block_bio_queue(q, bio);
- q->make_request_fn(q, bio);
- return;
+ return true;

end_io:
bio_endio(bio, err);
+ return false;
}

-/*
- * We only want one ->make_request_fn to be active at a time,
- * else stack usage with stacked devices could be a problem.
- * So use current->bio_list to keep a list of requests
- * submited by a make_request_fn function.
- * current->bio_list is also used as a flag to say if
- * generic_make_request is currently active in this task or not.
- * If it is NULL, then no make_request is active. If it is non-NULL,
- * then a make_request is active, and new requests should be added
- * at the tail
+/**
+ * generic_make_request - hand a buffer to its device driver for I/O
+ * @bio: The bio describing the location in memory and on the device.
+ *
+ * generic_make_request() is used to make I/O requests of block
+ * devices. It is passed a &struct bio, which describes the I/O that needs
+ * to be done.
+ *
+ * generic_make_request() does not return any status. The
+ * success/failure status of the request, along with notification of
+ * completion, is delivered asynchronously through the bio->bi_end_io
+ * function described (one day) else where.
+ *
+ * The caller of generic_make_request must make sure that bi_io_vec
+ * are set to describe the memory buffer, and that bi_dev and bi_sector are
+ * set to describe the device address, and the
+ * bi_end_io and optionally bi_private are set to describe how
+ * completion notification should be signaled.
+ *
+ * generic_make_request and the drivers it calls may use bi_next if this
+ * bio happens to be merged with someone else, and may resubmit the bio to
+ * a lower device by calling into generic_make_request recursively, which
+ * means the bio should NOT be touched after the call to ->make_request_fn.
*/
void generic_make_request(struct bio *bio)
{
struct bio_list bio_list_on_stack;

+ if (!generic_make_request_checks(bio))
+ return;
+
+ /*
+ * We only want one ->make_request_fn to be active at a time, else
+ * stack usage with stacked devices could be a problem. So use
+ * current->bio_list to keep a list of requests submited by a
+ * make_request_fn function. current->bio_list is also used as a
+ * flag to say if generic_make_request is currently active in this
+ * task or not. If it is NULL, then no make_request is active. If
+ * it is non-NULL, then a make_request is active, and new requests
+ * should be added at the tail
+ */
if (current->bio_list) {
- /* make_request is active */
bio_list_add(current->bio_list, bio);
return;
}
+
/* following loop may be a bit non-obvious, and so deserves some
* explanation.
* Before entering the loop, bio->bi_next is NULL (as all callers
@@ -1557,16 +1561,15 @@ void generic_make_request(struct bio *bi
* from the top. In this case we really did just take the bio
* of the top of the list (no pretending) and so remove it from
* bio_list, and call into __generic_make_request again.
- *
- * The loop was structured like this to make only one call to
- * __generic_make_request (which is important as it is large and
- * inlined) and to keep the structure simple.
*/
BUG_ON(bio->bi_next);
bio_list_init(&bio_list_on_stack);
current->bio_list = &bio_list_on_stack;
do {
- __generic_make_request(bio);
+ struct request_queue *q = bdev_get_queue(bio->bi_bdev);
+
+ q->make_request_fn(q, bio);
+
bio = bio_list_pop(current->bio_list);
} while (bio);
current->bio_list = NULL; /* deactivate */

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Old 09-12-2011, 03:09 PM
Vivek Goyal
 
Default block: refactor generic_make_request

On Mon, Sep 12, 2011 at 09:42:02AM -0400, Christoph Hellwig wrote:

[..]
> +
> /* following loop may be a bit non-obvious, and so deserves some
> * explanation.
> * Before entering the loop, bio->bi_next is NULL (as all callers
> @@ -1557,16 +1561,15 @@ void generic_make_request(struct bio *bi
> * from the top. In this case we really did just take the bio
> * of the top of the list (no pretending) and so remove it from
> * bio_list, and call into __generic_make_request again.
^^^^^^^^^^
You got rid of __generic_make_request(). Now above comment has stale
reference to it.

Thanks
Vivek

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Old 09-12-2011, 03:13 PM
Christoph Hellwig
 
Default block: refactor generic_make_request

On Mon, Sep 12, 2011 at 11:09:35AM -0400, Vivek Goyal wrote:
> On Mon, Sep 12, 2011 at 09:42:02AM -0400, Christoph Hellwig wrote:
>
> [..]
> > +
> > /* following loop may be a bit non-obvious, and so deserves some
> > * explanation.
> > * Before entering the loop, bio->bi_next is NULL (as all callers
> > @@ -1557,16 +1561,15 @@ void generic_make_request(struct bio *bi
> > * from the top. In this case we really did just take the bio
> > * of the top of the list (no pretending) and so remove it from
> > * bio_list, and call into __generic_make_request again.
> ^^^^^^^^^^
> You got rid of __generic_make_request(). Now above comment has stale
> reference to it.

Yeah, this should be ->make_request now.

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Old 09-15-2011, 11:55 AM
Christoph Hellwig
 
Default block: refactor generic_make_request

On Mon, Sep 12, 2011 at 11:13:10AM -0400, Christoph Hellwig wrote:
> > > @@ -1557,16 +1561,15 @@ void generic_make_request(struct bio *bi
> > > * from the top. In this case we really did just take the bio
> > > * of the top of the list (no pretending) and so remove it from
> > > * bio_list, and call into __generic_make_request again.
> > ^^^^^^^^^^
> > You got rid of __generic_make_request(). Now above comment has stale
> > reference to it.
>
> Yeah, this should be ->make_request now.

Jens, do you want me to resend with that fix or can you fix it up when
applying?

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Old 09-15-2011, 11:56 AM
Jens Axboe
 
Default block: refactor generic_make_request

On 2011-09-15 13:55, Christoph Hellwig wrote:
> On Mon, Sep 12, 2011 at 11:13:10AM -0400, Christoph Hellwig wrote:
>>>> @@ -1557,16 +1561,15 @@ void generic_make_request(struct bio *bi
>>>> * from the top. In this case we really did just take the bio
>>>> * of the top of the list (no pretending) and so remove it from
>>>> * bio_list, and call into __generic_make_request again.
>>> ^^^^^^^^^^
>>> You got rid of __generic_make_request(). Now above comment has stale
>>> reference to it.
>>
>> Yeah, this should be ->make_request now.
>
> Jens, do you want me to resend with that fix or can you fix it up when
> applying?

I'll just fix it up, applying it now.

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