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Commit 4cc1b4cf authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Alasdair G Kergon
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dm kcopyd: remove superfluous page allocation spinlock 



Remove the spinlock protecting the pages allocation.  The spinlock is only
taken on initialization or from single-threaded workqueue.  Therefore, the
spinlock is useless.

The spinlock is taken in kcopyd_get_pages and kcopyd_put_pages.

kcopyd_get_pages is only called from run_pages_job, which is only
called from process_jobs called from do_work.

kcopyd_put_pages is called from client_alloc_pages (which is initialization
function) or from run_complete_job. run_complete_job is only called from
process_jobs called from do_work.

Another spinlock, kc->job_lock is taken each time someone pushes or pops
some work for the worker thread.  Once we take kc->job_lock, we
guarantee that any written memory is visible to the other CPUs.

Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent c6ea41fb

drivers/md/dm-kcopyd.c

+1 −10
Original line number Diff line number Diff line
@@ -36,7 +36,6 @@ 
 * pages for kcopyd io.

 *---------------------------------------------------------------*/

struct dm_kcopyd_client {

	spinlock_t lock;

	struct page_list *pages;

	unsigned int nr_pages;

	unsigned int nr_free_pages;
@@ -99,11 +98,8 @@ static int kcopyd_get_pages(struct dm_kcopyd_client *kc, 
{

	struct page_list *pl;



	spin_lock(&kc->lock);

	if (kc->nr_free_pages < nr) {

		spin_unlock(&kc->lock);

	if (kc->nr_free_pages < nr)

		return -ENOMEM;

	}



	kc->nr_free_pages -= nr;

	for (*pages = pl = kc->pages; --nr; pl = pl->next)
@@ -112,8 +108,6 @@ static int kcopyd_get_pages(struct dm_kcopyd_client *kc, 
	kc->pages = pl->next;

	pl->next = NULL;



	spin_unlock(&kc->lock);



	return 0;

}
@@ -121,14 +115,12 @@ static void kcopyd_put_pages(struct dm_kcopyd_client *kc, struct page_list *pl) 
{

	struct page_list *cursor;



	spin_lock(&kc->lock);

	for (cursor = pl; cursor->next; cursor = cursor->next)

		kc->nr_free_pages++;



	kc->nr_free_pages++;

	cursor->next = kc->pages;

	kc->pages = pl;

	spin_unlock(&kc->lock);

}



/*
@@ -625,7 +617,6 @@ int dm_kcopyd_client_create(unsigned int nr_pages, 
	if (!kc)

		return -ENOMEM;



	spin_lock_init(&kc->lock);

	spin_lock_init(&kc->job_lock);

	INIT_LIST_HEAD(&kc->complete_jobs);

	INIT_LIST_HEAD(&kc->io_jobs);