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-   -   dm: convey that all flushes are processed as empty (http://www.linux-archive.org/device-mapper-development/424173-dm-convey-all-flushes-processed-empty.html)

Christoph Hellwig 09-08-2010 12:00 AM

dm: convey that all flushes are processed as empty
 
On Tue, Sep 07, 2010 at 07:49:18PM -0400, Mike Snitzer wrote:
> if (!(bio->bi_rw & REQ_FLUSH) || !bio->bi_size) {
> + /* done with normal IO or empty flush */
> trace_block_bio_complete(md->queue, bio);
> bio_endio(bio, io_error);
> } else {

To clarify this further I'd reorder the checks:

if ((bio->bi_rw & REQ_FLUSH) && bio->bi_size) {
/*
* Preflush done, ...
*/
} else {
}

> @@ -1302,20 +1302,17 @@ static void __split_and_process_bio(struct mapped_device *md, struct bio *bio)
> ci.sector = bio->bi_sector;
> ci.idx = bio->bi_idx;
>
> + start_io_acct(ci.io);
> if (!is_flush) {

no need for the is_flush anymore now that it's only used once. Again,
I think avoiding negatives without a reason in if statement usually
makes the code a bit more clear.

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Mike Snitzer 09-08-2010 02:04 AM

dm: convey that all flushes are processed as empty
 
Rename __clone_and_map_flush to __clone_and_map_empty_flush for added
clarity.

Simplify logic associated with REQ_FLUSH conditionals.

Introduce a BUG_ON() and add a few more helpful comments to the code
so that it is clear that all flushes are empty.

Cleanup __split_and_process_bio() so that an empty flush isn't processed
by a 'sector_count' focused while loop.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
---
drivers/md/dm.c | 34 +++++++++++++++-------------------
1 files changed, 15 insertions(+), 19 deletions(-)

Tejun, please feel free to fold this patch into (or insert after)
0025-dm-relax-ordering-of-bio-based-flush-implementation.patch

v2: Simplify logic associated with REQ_FLUSH conditionals

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index cd2f7e7..f934e98 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -621,16 +621,17 @@ static void dec_pending(struct dm_io *io, int error)
if (io_error == DM_ENDIO_REQUEUE)
return;

- if (!(bio->bi_rw & REQ_FLUSH) || !bio->bi_size) {
- trace_block_bio_complete(md->queue, bio);
- bio_endio(bio, io_error);
- } else {
+ if ((bio->bi_rw & REQ_FLUSH) && bio->bi_size) {
/*
* Preflush done for flush with data, reissue
* without REQ_FLUSH.
*/
bio->bi_rw &= ~REQ_FLUSH;
queue_io(md, bio);
+ } else {
+ /* done with normal IO or empty flush */
+ trace_block_bio_complete(md->queue, bio);
+ bio_endio(bio, io_error);
}
}
}
@@ -1132,16 +1133,15 @@ static void __issue_target_requests(struct clone_info *ci, struct dm_target *ti,
__issue_target_request(ci, ti, request_nr, len);
}

-static int __clone_and_map_flush(struct clone_info *ci)
+static int __clone_and_map_empty_flush(struct clone_info *ci)
{
unsigned target_nr = 0;
struct dm_target *ti;

+ BUG_ON(bio_has_data(ci->bio));
while ((ti = dm_table_get_target(ci->map, target_nr++)))
__issue_target_requests(ci, ti, ti->num_flush_requests, 0);

- ci->sector_count = 0;
-
return 0;
}

@@ -1282,7 +1282,6 @@ static int __clone_and_map(struct clone_info *ci)
*/
static void __split_and_process_bio(struct mapped_device *md, struct bio *bio)
{
- bool is_flush = bio->bi_rw & REQ_FLUSH;
struct clone_info ci;
int error = 0;

@@ -1302,20 +1301,17 @@ static void __split_and_process_bio(struct mapped_device *md, struct bio *bio)
ci.sector = bio->bi_sector;
ci.idx = bio->bi_idx;

- if (!is_flush) {
+ start_io_acct(ci.io);
+ if (bio->bi_rw & REQ_FLUSH) {
+ ci.bio = &ci.md->flush_bio;
+ ci.sector_count = 0;
+ error = __clone_and_map_empty_flush(&ci);
+ /* dec_pending submits any data associated with flush */
+ } else {
ci.bio = bio;
ci.sector_count = bio_sectors(bio);
- } else {
- ci.bio = &ci.md->flush_bio;
- ci.sector_count = 1;
- }
-
- start_io_acct(ci.io);
- while (ci.sector_count && !error) {
- if (!is_flush)
+ while (ci.sector_count && !error)
error = __clone_and_map(&ci);
- else
- error = __clone_and_map_flush(&ci);
}

/* drop the extra reference count */

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