[2.4] heavy-load under swap space shortage

[j-nomura]

Hello,

swap_out() seems always trying scan even if there are no swap space available.
This keeps CPU(s) busy with rare successful page-out and may cause lock
contention in big smp system.

  swap_out()
    ..
    try_to_swap_out()
      ..
      entry = get_swap_page()
      /* find no swap page available */

How about checking nr_swap_pages first and giving up if it's 0?
Applying the patch below extremely reduced systime consumption by swap_out
under swap space shortage.

Systems without swap also suffer from the same problem.

Any comments?

Best regards.
--
NOMURA, Jun'ichi <j-nomura@xxxxxxxxxxxxx>

--- linux-2.4.24/mm/vmscan.c
+++ linux/mm/vmscan.c
@@ -326,8 +326,11 @@ out_unlock:
 static int swap_out(zone_t * classzone)
 {
 	int counter, nr_pages = SWAP_CLUSTER_MAX;
 	struct mm_struct *mm;
+
+	if (nr_swap_pages <= 0)
+		return 0;
 
 	counter = mmlist_nr << 1;
 	do {
		if (unlikely(current->need_resched)) {

-
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