dm kcopyd: remove superfluous page allocation spinlock (4cc1b4cf) · Commits · 戴 / test

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:

Mikulas Patocka <mpatocka@redhat.com> Signed-off-by:

Alasdair G Kergon <agk@redhat.com>

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);

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