[Xen-changelog] [xen-unstable] page scrub: Serialise softirq with a new lock.

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1218453611 -3600
# Node ID 32aa43364f5d8e19389d1f72d9b0bf51e198152f
# Parent  ce085fc0d2e423aa1c602ce117cc775b000470ba
page scrub: Serialise softirq with a new lock.
Avoids holding up acquiring page_scrub_lock in free_domheap_pages().

Signed-off-by: Keir Fraser <keir.fraser@xxxxxxxxxx>
---
 xen/common/page_alloc.c |   14 ++++++++++----
 1 files changed, 10 insertions(+), 4 deletions(-)

diff -r ce085fc0d2e4 -r 32aa43364f5d xen/common/page_alloc.c
--- a/xen/common/page_alloc.c   Mon Aug 11 11:27:40 2008 +0100
+++ b/xen/common/page_alloc.c   Mon Aug 11 12:20:11 2008 +0100
@@ -950,9 +950,10 @@ static void page_scrub_softirq(void)
     void             *p;
     int               i;
     s_time_t          start = NOW();
+    static spinlock_t serialise_lock = SPIN_LOCK_UNLOCKED;
 
     /* free_heap_pages() does not parallelise well. Serialise this function. */
-    if ( !spin_trylock(&page_scrub_lock) )
+    if ( !spin_trylock(&serialise_lock) )
     {
         set_timer(&this_cpu(page_scrub_timer), NOW() + MILLISECS(1));
         return;
@@ -960,10 +961,12 @@ static void page_scrub_softirq(void)
 
     /* Aim to do 1ms of work every 10ms. */
     do {
+        spin_lock(&page_scrub_lock);
+
         if ( unlikely((ent = page_scrub_list.next) == &page_scrub_list) )
         {
             spin_unlock(&page_scrub_lock);
-            return;
+            goto out;
         }
         
         /* Peel up to 16 pages from the list. */
@@ -978,6 +981,8 @@ static void page_scrub_softirq(void)
         ent->next->prev = &page_scrub_list;
         page_scrub_list.next = ent->next;
         scrub_pages -= (i+1);
+
+        spin_unlock(&page_scrub_lock);
 
         /* Working backwards, scrub each page in turn. */
         while ( ent != &page_scrub_list )
@@ -991,9 +996,10 @@ static void page_scrub_softirq(void)
         }
     } while ( (NOW() - start) < MILLISECS(1) );
 
-    spin_unlock(&page_scrub_lock);
-
     set_timer(&this_cpu(page_scrub_timer), NOW() + MILLISECS(10));
+
+ out:
+    spin_unlock(&serialise_lock);
 }
 
 static void page_scrub_timer_fn(void *unused)

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