From dc1b30224f9b1587dbe383d9c8e16caa4b1f71d3 Mon Sep 17 00:00:00 2001
From: Brian Behlendorf <behlendorf1@llnl.gov>
Date: Mon, 5 Nov 2012 13:54:20 -0800
Subject: [PATCH] Never spin in kmem_cache_alloc()
If we are reaping from the cache and a concurrent allocation
occurs then the caller must block until the reaping is complete.
This is signaled by the clearing of the KMC_BIT_REAPING bit.
Otherwise the caller will be in a tight loop which takes and
releases the skc->skc_cache lock. When there are multiple
concurrent callers the system will thrash on the lock and
appear to lock up.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
---
module/spl/spl-kmem.c | 22 +++++++++++++++++-----
1 file changed, 17 insertions(+), 5 deletions(-)
diff --git a/module/spl/spl-kmem.c b/module/spl/spl-kmem.c
index 5627b5590b..f3113e0f49 100644
--- a/module/spl/spl-kmem.c
+++ b/module/spl/spl-kmem.c
@@ -1725,6 +1725,13 @@ spl_cache_grow_wait(spl_kmem_cache_t *skc)
return !test_bit(KMC_BIT_GROWING, &skc->skc_flags);
}
+static int
+spl_cache_reclaim_wait(void *word)
+{
+ schedule();
+ return 0;
+}
+
/*
* No available objects on any slabs, create a new slab.
*/
@@ -1739,12 +1746,14 @@ spl_cache_grow(spl_kmem_cache_t *skc, int flags, void **obj)
*obj = NULL;
/*
- * Before allocating a new slab check if the slab is being reaped.
- * If it is there is a good chance we can wait until it finishes
- * and then use one of the newly freed but not aged-out slabs.
+ * Before allocating a new slab wait for any reaping to complete and
+ * then return so the local magazine can be rechecked for new objects.
*/
- if (test_bit(KMC_BIT_REAPING, &skc->skc_flags))
- SRETURN(-EAGAIN);
+ if (test_bit(KMC_BIT_REAPING, &skc->skc_flags)) {
+ rc = wait_on_bit(&skc->skc_flags, KMC_BIT_REAPING,
+ spl_cache_reclaim_wait, TASK_UNINTERRUPTIBLE);
+ SRETURN(rc ? rc : -EAGAIN);
+ }
/*
* This is handled by dispatching a work request to the global work
@@ -2156,6 +2165,9 @@ spl_kmem_cache_reap_now(spl_kmem_cache_t *skc, int count)
/* Reclaim from the cache, ignoring it's age and delay. */
spl_slab_reclaim(skc, count, 1);
clear_bit(KMC_BIT_REAPING, &skc->skc_flags);
+ smp_mb__after_clear_bit();
+ wake_up_bit(&skc->skc_flags, KMC_BIT_REAPING);
+
atomic_dec(&skc->skc_ref);
SEXIT;