From: Ingo Molnar <mingo@elte.hu>
The attached patch fixes long scheduling latencies in select_parent() and
prune_dcache(). The prune_dcache() lock-break is easy, but for
select_parent() the only viable solution i found was to break out if
there's a resched necessary - the reordering is not necessary and the
dcache scanning/shrinking will later on do it anyway.
This patch has been in the -VP patchset for weeks.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/fs/dcache.c | 11 +++++++++++
1 files changed, 11 insertions(+)
diff -puN fs/dcache.c~sched-vfs-fix-scheduling-latencies-in-prune_dcache-and-select_parent fs/dcache.c
--- 25/fs/dcache.c~sched-vfs-fix-scheduling-latencies-in-prune_dcache-and-select_parent 2004-09-30 22:36:07.108790904 -0700
+++ 25-akpm/fs/dcache.c 2004-09-30 22:36:07.113790144 -0700
@@ -388,6 +388,8 @@ static void prune_dcache(int count)
struct dentry *dentry;
struct list_head *tmp;
+ cond_resched_lock(&dcache_lock);
+
tmp = dentry_unused.prev;
if (tmp == &dentry_unused)
break;
@@ -560,6 +562,14 @@ resume:
struct dentry *dentry = list_entry(tmp, struct dentry, d_child);
next = tmp->next;
+ /*
+ * select_parent() is a performance optimization, it is
+ * not necessary to complete it. Abort if a reschedule is
+ * pending:
+ */
+ if (need_resched())
+ goto out;
+
if (!list_empty(&dentry->d_lru)) {
dentry_stat.nr_unused--;
list_del_init(&dentry->d_lru);
@@ -597,6 +607,7 @@ this_parent->d_parent->d_name.name, this
#endif
goto resume;
}
+out:
spin_unlock(&dcache_lock);
return found;
}
_