From 52b7efdbe5f5696fc80338560a3fc51e0b0a993c Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Sat, 3 Sep 2005 15:54:39 -0700 Subject: [PATCH] swap: scan_swap_map drop swap_device_lock get_swap_page has often shown up on latency traces, doing lengthy scans while holding two spinlocks. swap_list_lock is already dropped, now scan_swap_map drop swap_device_lock before scanning the swap_map. While scanning for an empty cluster, don't worry that racing tasks may allocate what was free and free what was allocated; but when allocating an entry, check it's still free after retaking the lock. Avoid dropping the lock in the expected common path. No barriers beyond the locks, just let the cookie crumble; highest_bit limit is volatile, but benign. Guard against swapoff: must check SWP_WRITEOK before allocating, must raise SWP_SCANNING reference count while in scan_swap_map, swapoff wait for that to fall - just use schedule_timeout, we don't want to burden scan_swap_map itself, and it's very unlikely that anyone can really still be in scan_swap_map once swapoff gets this far. Signed-off-by: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/swap.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include/linux') diff --git a/include/linux/swap.h b/include/linux/swap.h index 93f0eca7f91..db3b5de7c92 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -107,6 +107,8 @@ enum { SWP_USED = (1 << 0), /* is slot in swap_info[] used? */ SWP_WRITEOK = (1 << 1), /* ok to write to this swap? */ SWP_ACTIVE = (SWP_USED | SWP_WRITEOK), + /* add others here before... */ + SWP_SCANNING = (1 << 8), /* refcount in scan_swap_map */ }; #define SWAP_CLUSTER_MAX 32 -- cgit v1.2.3