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dm kcopyd: accept zero size jobs 

dm-kcopyd: accept zero-size jobs

This patch changes dm-kcopyd so that it accepts zero-size jobs and completes
them immediatelly via its completion thread.

It is needed for multisnapshots snapshot resizing. When we are writing to
a chunk beyond origin end, no copying is done. To simplify the code, we submit
an empty request to kcopyd and let kcopyd complete it. If we didn't submit
a request to kcopyd and called the completion routine immediatelly, it would
violate the principle that completion is called only from one thread and
it would need additional locking.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Mikulas Patocka 2009-12-10 23:52:13 +00:00 committed by Alasdair G Kergon
parent c26655ca3c
commit 9ca170a3c0
1 changed files with 4 additions and 1 deletions
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5
drivers/md/dm-kcopyd.c
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@ -450,7 +450,10 @@ static void dispatch_job(struct kcopyd_job *job)
{ {
struct dm_kcopyd_client *kc = job->kc; struct dm_kcopyd_client *kc = job->kc;
atomic_inc(&kc->nr_jobs); atomic_inc(&kc->nr_jobs);
push(&kc->pages_jobs, job); if (unlikely(!job->source.count))
push(&kc->complete_jobs, job);
else
push(&kc->pages_jobs, job);
wake(kc); wake(kc);
} }