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Commit f9efa9c7 authored by Chris Mason's avatar Chris Mason
Browse files

Btrfs: Reduce contention on the root node 



This calls unlock_up sooner in btrfs_search_slot in order to decrease the
amount of work done with the higher level tree locks held.

Also, it changes btrfs_tree_lock to spin for a big against the page lock
before scheduling.  This makes a big difference in context switch rate under
highly contended workloads.

Longer term, a better locking structure is needed than the page lock.

Signed-off-by: default avatarChris Mason <chris.mason@oracle.com>
parent 3f157a2f

fs/btrfs/ctree.c

+11 −6
Original line number Diff line number Diff line
@@ -1313,16 +1313,13 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root 
				slot = p->slots[level];

				BUG_ON(btrfs_header_nritems(b) == 1);

			}

			unlock_up(p, level, lowest_unlock);



			/* this is only true while dropping a snapshot */

			if (level == lowest_level) {

				unlock_up(p, level, lowest_unlock);

				break;

			}



			if (should_reada)

				reada_for_search(root, p, level, slot,

						 key->objectid);



			blocknr = btrfs_node_blockptr(b, slot);

			gen = btrfs_node_ptr_generation(b, slot);

			blocksize = btrfs_level_size(root, level - 1);
@@ -1340,6 +1337,11 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root 
					btrfs_release_path(NULL, p);

					if (tmp)

						free_extent_buffer(tmp);

					if (should_reada)

						reada_for_search(root, p,

								 level, slot,

								 key->objectid);



					tmp = read_tree_block(root, blocknr,

							 blocksize, gen);

					if (tmp)
@@ -1348,12 +1350,15 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root 
				} else {

					if (tmp)

						free_extent_buffer(tmp);

					if (should_reada)

						reada_for_search(root, p,

								 level, slot,

								 key->objectid);

					b = read_node_slot(root, b, slot);

				}

			}

			if (!p->skip_locking)

				btrfs_tree_lock(b);

			unlock_up(p, level, lowest_unlock);

		} else {

			p->slots[level] = slot;

			if (ins_len > 0 && btrfs_leaf_free_space(root, b) <

fs/btrfs/locking.c

+10 −0
Original line number Diff line number Diff line
@@ -27,6 +27,16 @@ 


int btrfs_tree_lock(struct extent_buffer *eb)

{

	int i;



	if (!TestSetPageLocked(eb->first_page))

		return 0;

	for (i = 0; i < 512; i++) {

		cpu_relax();

		if (!TestSetPageLocked(eb->first_page))

			return 0;

	}

	cpu_relax();

	lock_page(eb->first_page);

	return 0;

}