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	Original line	Diff line number	Diff line
	@@ -672,6 +672,9 @@ static int scan_swap_map_slots(struct swap_info_struct *si,
	else		else
	goto done;		goto done;
	}		}
			si->swap_map[offset] = usage;
			inc_cluster_info_page(si, si->cluster_info, offset);
			unlock_cluster(ci);

	if (offset == si->lowest_bit)		if (offset == si->lowest_bit)
	si->lowest_bit++;		si->lowest_bit++;
	@@ -685,9 +688,6 @@ static int scan_swap_map_slots(struct swap_info_struct *si,
	plist_del(&si->avail_list, &swap_avail_head);		plist_del(&si->avail_list, &swap_avail_head);
	spin_unlock(&swap_avail_lock);		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;		si->cluster_next = offset + 1;
	slots[n_ret++] = swp_entry(si->type, offset);		slots[n_ret++] = swp_entry(si->type, offset);