From fb4f88dcabdc716c7c350e09cf4a38a419b007e1 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Sat, 3 Sep 2005 15:54:37 -0700 Subject: [PATCH] [PATCH] swap: get_swap_page drop swap_list_lock Rewrite get_swap_page to allocate in just the same sequence as before, but without holding swap_list_lock across its scan_swap_map. Decrement nr_swap_pages and update swap_list.next in advance, while still holding swap_list_lock. Skip full devices by testing highest_bit. Swapoff hold swap_device_lock as well as swap_list_lock to clear SWP_WRITEOK. Reduces lock contention when there are parallel swap devices of the same priority. Signed-off-by: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/swapfile.c | 73 ++++++++++++++++++++++++--------------------------- 1 file changed, 35 insertions(+), 38 deletions(-) diff --git a/mm/swapfile.c b/mm/swapfile.c index 62e0da8f7e6e..e54d60af6b58 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -139,7 +139,6 @@ static inline unsigned long scan_swap_map(struct swap_info_struct *si) } si->swap_map[offset] = 1; si->inuse_pages++; - nr_swap_pages--; si->cluster_next = offset+1; return offset; } @@ -150,50 +149,45 @@ static inline unsigned long scan_swap_map(struct swap_info_struct *si) swp_entry_t get_swap_page(void) { - struct swap_info_struct * p; - unsigned long offset; - swp_entry_t entry; - int type, wrapped = 0; + struct swap_info_struct *si; + pgoff_t offset; + int type, next; + int wrapped = 0; - entry.val = 0; /* Out of memory */ swap_list_lock(); - type = swap_list.next; - if (type < 0) - goto out; if (nr_swap_pages <= 0) - goto out; + goto noswap; + nr_swap_pages--; - while (1) { - p = &swap_info[type]; - if ((p->flags & SWP_ACTIVE) == SWP_ACTIVE) { - swap_device_lock(p); - offset = scan_swap_map(p); - swap_device_unlock(p); - if (offset) { - entry = swp_entry(type,offset); - type = swap_info[type].next; - if (type < 0 || - p->prio != swap_info[type].prio) { - swap_list.next = swap_list.head; - } else { - swap_list.next = type; - } - goto out; - } + for (type = swap_list.next; type >= 0 && wrapped < 2; type = next) { + si = swap_info + type; + next = si->next; + if (next < 0 || + (!wrapped && si->prio != swap_info[next].prio)) { + next = swap_list.head; + wrapped++; } - type = p->next; - if (!wrapped) { - if (type < 0 || p->prio != swap_info[type].prio) { - type = swap_list.head; - wrapped = 1; - } - } else - if (type < 0) - goto out; /* out of swap space */ + + if (!si->highest_bit) + continue; + if (!(si->flags & SWP_WRITEOK)) + continue; + + swap_list.next = next; + swap_device_lock(si); + swap_list_unlock(); + offset = scan_swap_map(si); + swap_device_unlock(si); + if (offset) + return swp_entry(type, offset); + swap_list_lock(); + next = swap_list.next; } -out: + + nr_swap_pages++; +noswap: swap_list_unlock(); - return entry; + return (swp_entry_t) {0}; } static struct swap_info_struct * swap_info_get(swp_entry_t entry) @@ -1105,8 +1099,11 @@ asmlinkage long sys_swapoff(const char __user * specialfile) } nr_swap_pages -= p->pages; total_swap_pages -= p->pages; + swap_device_lock(p); p->flags &= ~SWP_WRITEOK; + swap_device_unlock(p); swap_list_unlock(); + current->flags |= PF_SWAPOFF; err = try_to_unuse(type); current->flags &= ~PF_SWAPOFF;