Commit 2872bb2d authored May 03, 2017 by Huang Ying Committed by Linus Torvalds May 03, 2017

mm, swap: avoid lock swap_avail_lock when held cluster lock

Cluster lock is used to protect the swap_cluster_info and corresponding
elements in swap_info_struct->swap_map[]. But it is found that now in
scan_swap_map_slots(), swap_avail_lock may be acquired when cluster lock
is held. This does no good except making the locking more complex and
improving the potential locking contention, because the
swap_info_struct->lock is used to protect the data structure operated in
the code already. Fix this via moving the corresponding operations in
scan_swap_map_slots() out of cluster lock.

Link: http://lkml.kernel.org/r/20170317064635.12792-3-ying.huang@intel.com

Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Acked-by: Tim Chen <tim.c.chen@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 0ef017d1

mm/swapfile.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -672,6 +672,9 @@ checks:
		else
		goto done;
		}
		si->swap_map[offset] = usage;
		inc_cluster_info_page(si, si->cluster_info, offset);
		unlock_cluster(ci);

		if (offset == si->lowest_bit)
		si->lowest_bit++;
		@@ -685,9 +688,6 @@ checks:
		plist_del(&si->avail_list, &swap_avail_head);
		spin_unlock(&swap_avail_lock);
		}
		si->swap_map[offset] = usage;
		inc_cluster_info_page(si, si->cluster_info, offset);
		unlock_cluster(ci);
		si->cluster_next = offset + 1;
		slots[n_ret++] = swp_entry(si->type, offset);