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 <[email protected]>
---
mm/swapfile.c | 73 +++++++++++++++++++++++++++-------------------------------
1 files changed, 35 insertions(+), 38 deletions(-)
--- swap7/mm/swapfile.c 2005-07-08 19:14:39.000000000 +0100
+++ swap8/mm/swapfile.c 2005-07-08 19:14:54.000000000 +0100
@@ -137,7 +137,6 @@ static inline unsigned long scan_swap_ma
}
si->swap_map[offset] = 1;
si->inuse_pages++;
- nr_swap_pages--;
si->cluster_next = offset+1;
return offset;
}
@@ -148,50 +147,45 @@ static inline unsigned long scan_swap_ma
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)
@@ -1103,8 +1097,11 @@ asmlinkage long sys_swapoff(const char _
}
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;
-
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