mm/swap: enable swap slots cache usage

Initialize swap slots cache and enable it on swap on.  Drain all swap
slots on swap off.

Link: http://lkml.kernel.org/r/07cbc94882fa95d4ac3cfc50b8dce0b1ec231b93.1484082593.git.tim.c.chen@linux.intel.com
Signed-off-by: Tim Chen <[email protected]>
Cc: "Huang, Ying" <[email protected]>
Cc: Aaron Lu <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Christian Borntraeger <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Hillf Danton <[email protected]>
Cc: Huang Ying <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Jonathan Corbet <[email protected]> escreveu:
Cc: Kirill A. Shutemov <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Shaohua Li <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/swapfile.c

@@ -2190,16 +2190,21 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	spin_unlock(&p->lock);
 	spin_unlock(&swap_lock);
 
+	disable_swap_slots_cache_lock();
+
 	set_current_oom_origin();
 	err = try_to_unuse(p->type, false, 0); /* force unuse all pages */
 	clear_current_oom_origin();
 
 	if (err) {
 		/* re-insert swap space back into swap_list */
 		reinsert_swap_info(p);
+		reenable_swap_slots_cache_unlock();
 		goto out_dput;
 	}
 
+	reenable_swap_slots_cache_unlock();
+
 	flush_work(&p->discard_work);
 
 	destroy_swap_extents(p);
@@ -2886,6 +2891,8 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 		putname(name);
 	if (inode && S_ISREG(inode->i_mode))
 		inode_unlock(inode);
+	if (!error)
+		enable_swap_slots_cache();
 	return error;
 }