dm kcopyd: add WRITE SAME support to dm_kcopyd_zero
Add WRITE SAME support to dm-io and make it accessible to
dm_kcopyd_zero(). dm_kcopyd_zero() provides an asynchronous interface
whereas the blkdev_issue_write_same() interface is synchronous.
WRITE SAME is a SCSI command that can be leveraged for more efficient
zeroing of a specified logical extent of a device which supports it.
Only a single zeroed logical block is transfered to the target for each
WRITE SAME and the target then writes that same block across the
specified extent.
The dm thin target uses this.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/drivers/md/dm-kcopyd.c b/drivers/md/dm-kcopyd.c
index bed444c..68c0267 100644
--- a/drivers/md/dm-kcopyd.c
+++ b/drivers/md/dm-kcopyd.c
@@ -349,7 +349,7 @@
struct dm_kcopyd_client *kc = job->kc;
if (error) {
- if (job->rw == WRITE)
+ if (job->rw & WRITE)
job->write_err |= error;
else
job->read_err = 1;
@@ -361,7 +361,7 @@
}
}
- if (job->rw == WRITE)
+ if (job->rw & WRITE)
push(&kc->complete_jobs, job);
else {
@@ -432,7 +432,7 @@
if (r < 0) {
/* error this rogue job */
- if (job->rw == WRITE)
+ if (job->rw & WRITE)
job->write_err = (unsigned long) -1L;
else
job->read_err = 1;
@@ -585,6 +585,7 @@
unsigned int flags, dm_kcopyd_notify_fn fn, void *context)
{
struct kcopyd_job *job;
+ int i;
/*
* Allocate an array of jobs consisting of one master job
@@ -611,7 +612,16 @@
memset(&job->source, 0, sizeof job->source);
job->source.count = job->dests[0].count;
job->pages = &zero_page_list;
- job->rw = WRITE;
+
+ /*
+ * Use WRITE SAME to optimize zeroing if all dests support it.
+ */
+ job->rw = WRITE | REQ_WRITE_SAME;
+ for (i = 0; i < job->num_dests; i++)
+ if (!bdev_write_same(job->dests[i].bdev)) {
+ job->rw = WRITE;
+ break;
+ }
}
job->fn = fn;