[RFC][PATCH 2/4] dm-log: unify rw_header to read/write_header

[RFC][PATCH 2/4] dm-log: unify rw_header to read/write_header

[Takahiro Yasui]

rw_header function updates three members of io_req data every time
when I/O is processed. bi_rw and notify.fn are never modified once
they get initialized, and also they can be set in advance.
This patch removes unnecessary update operations.


Signed-off-by: Takahiro Yasui <tyasui@redhat.com>
---
 drivers/md/dm-log.c |   23 +++++++++++------------
 1 file changed, 11 insertions(+), 12 deletions(-)

Index: linux-2.6.28-rc4/drivers/md/dm-log.c
===================================================================
--- linux-2.6.28-rc4.orig/drivers/md/dm-log.c
+++ linux-2.6.28-rc4/drivers/md/dm-log.c
@@ -323,20 +323,13 @@ static void header_from_disk(struct log_
 	core->nr_regions = le64_to_cpu(disk->nr_regions);
 }
 
-static int rw_header(struct log_c *lc, int rw)
-{
-	lc->io_req.bi_rw = rw;
-	lc->io_req.mem.ptr.vma = lc->disk_header;
-	lc->io_req.notify.fn = NULL;
-
-	return dm_io(&lc->io_req, 1, &lc->header_location, NULL);
-}
-
 static int read_header(struct log_c *log)
 {
 	int r;
 
-	r = rw_header(log, READ);
+	log->io_req.bi_rw = READ;
+
+	r = dm_io(&log->io_req, 1, &log->header_location, NULL);
 	if (r)
 		return r;
 
@@ -364,8 +357,8 @@ static int read_header(struct log_c *log
 
 static inline int write_header(struct log_c *log)
 {
-	header_to_disk(&log->header, log->disk_header);
-	return rw_header(log, WRITE);
+	log->io_req.bi_rw = WRITE;
+	return dm_io(&log->io_req, 1, &log->header_location, NULL);
 }
 
 /*----------------------------------------------------------------
@@ -454,7 +447,10 @@ static int create_log_context(struct dm_
 		buf_size = dm_round_up((LOG_OFFSET << SECTOR_SHIFT) +
 				       bitset_size, ti->limits.hardsect_size);
 		lc->header_location.count = buf_size >> SECTOR_SHIFT;
+
 		lc->io_req.mem.type = DM_IO_VMA;
+		lc->io_req.mem.ptr.vma = lc->disk_header;
+		lc->io_req.notify.fn = NULL;
 		lc->io_req.client = dm_io_client_create(dm_div_up(buf_size,
 								   PAGE_SIZE));
 		if (IS_ERR(lc->io_req.client)) {
@@ -636,6 +632,9 @@ static int disk_resume(struct dm_dirty_l
 	/* set the correct number of regions in the header */
 	lc->header.nr_regions = lc->region_count;
 
+	/* update disk headers */
+	header_to_disk(&lc->header, lc->disk_header);
+
 	/* write the new header */
 	r = write_header(lc);
 	if (r) {

Re: [RFC][PATCH 2/4] dm-log: unify rw_header to read/write_header

[Alasdair G Kergon]

On Tue, Nov 25, 2008 at 07:01:39PM -0500, Takahiro Yasui wrote:
> rw_header function updates three members of io_req data every time
> when I/O is processed. bi_rw and notify.fn are never modified once
> they get initialized, and also they can be set in advance.
> This patch removes unnecessary update operations.
 
Indeed.

And it also removes header_to_disk() from the disk_flush() code
path but doesn't mention changing that:-)  I assume that's also
OK because there'll always have been a resume before the flush
and the data can only change during a resume?
 
> +++ linux-2.6.28-rc4/drivers/md/dm-log.c
> @@ -323,20 +323,13 @@ static void header_from_disk(struct log_

> -static int rw_header(struct log_c *lc, int rw)

I reckon that little function improves readability/maintainability and I've
left it in.

http://www.kernel.org/pub/linux/kernel/people/agk/patches/2.6/editing/
    dm-log-avoid-reinitialising-io_req-on-every-operation.patch

Alasdair
-- 
agk@redhat.com

Re: [RFC][PATCH 2/4] dm-log: unify rw_header to read/write_header

[Takahiro Yasui]

Alasdair G Kergon wrote:
> On Tue, Nov 25, 2008 at 07:01:39PM -0500, Takahiro Yasui wrote:
>> rw_header function updates three members of io_req data every time
>> when I/O is processed. bi_rw and notify.fn are never modified once
>> they get initialized, and also they can be set in advance.
>> This patch removes unnecessary update operations.
>  
> Indeed.
> 
> And it also removes header_to_disk() from the disk_flush() code
> path but doesn't mention changing that:-)  I assume that's also
> OK because there'll always have been a resume before the flush
> and the data can only change during a resume?

Oh, I'm sorry not to mention it on the patch description, but
your explanation is exactly what I need to do.

>> +++ linux-2.6.28-rc4/drivers/md/dm-log.c
>> @@ -323,20 +323,13 @@ static void header_from_disk(struct log_
> 
>> -static int rw_header(struct log_c *lc, int rw)
> 
> I reckon that little function improves readability/maintainability and I've
> left it in.
> 
> http://www.kernel.org/pub/linux/kernel/people/agk/patches/2.6/editing/
>     dm-log-avoid-reinitialising-io_req-on-every-operation.patch

Thanks, Alasdair. I have removed rw_header function in my patch
since the last two patches don't use it, but your improvement is
fine as a separate patch.

Thanks,
---
Takahiro Yasui
Hitachi Computer Products (America) Inc.