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authorNathan Zimmer <nzimmer@sgi.com>2016-01-15 02:18:36 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2016-01-15 03:00:49 +0300
commit4a8c7bb59ac85b038c29adf6d32ff56e11fbb267 (patch)
tree76ded28807d90dab68c27f1d33412209be004d27 /mm/mempolicy.c
parent8f235d1a3eb7198affe7cadf676a10afb8a46a1a (diff)
downloadlinux-4a8c7bb59ac85b038c29adf6d32ff56e11fbb267.tar.xz
mm/mempolicy.c: convert the shared_policy lock to a rwlock
When running the SPECint_rate gcc on some very large boxes it was noticed that the system was spending lots of time in mpol_shared_policy_lookup(). The gamess benchmark can also show it and is what I mostly used to chase down the issue since the setup for that I found to be easier. To be clear the binaries were on tmpfs because of disk I/O requirements. We then used text replication to avoid icache misses and having all the copies banging on the memory where the instruction code resides. This results in us hitting a bottleneck in mpol_shared_policy_lookup() since lookup is serialised by the shared_policy lock. I have only reproduced this on very large (3k+ cores) boxes. The problem starts showing up at just a few hundred ranks getting worse until it threatens to livelock once it gets large enough. For example on the gamess benchmark at 128 ranks this area consumes only ~1% of time, at 512 ranks it consumes nearly 13%, and at 2k ranks it is over 90%. To alleviate the contention in this area I converted the spinlock to an rwlock. This allows a large number of lookups to happen simultaneously. The results were quite good reducing this consumtion at max ranks to around 2%. [akpm@linux-foundation.org: tidy up code comments] Signed-off-by: Nathan Zimmer <nzimmer@sgi.com> Acked-by: David Rientjes <rientjes@google.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Nadia Yvette Chambers <nyc@holomorphy.com> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Mel Gorman <mgorman@suse.de> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/mempolicy.c')
-rw-r--r--mm/mempolicy.c30
1 files changed, 17 insertions, 13 deletions
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 87a177917cb2..d8caff071a30 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2142,12 +2142,14 @@ bool __mpol_equal(struct mempolicy *a, struct mempolicy *b)
*
* Remember policies even when nobody has shared memory mapped.
* The policies are kept in Red-Black tree linked from the inode.
- * They are protected by the sp->lock spinlock, which should be held
+ * They are protected by the sp->lock rwlock, which should be held
* for any accesses to the tree.
*/
-/* lookup first element intersecting start-end */
-/* Caller holds sp->lock */
+/*
+ * lookup first element intersecting start-end. Caller holds sp->lock for
+ * reading or for writing
+ */
static struct sp_node *
sp_lookup(struct shared_policy *sp, unsigned long start, unsigned long end)
{
@@ -2178,8 +2180,10 @@ sp_lookup(struct shared_policy *sp, unsigned long start, unsigned long end)
return rb_entry(n, struct sp_node, nd);
}
-/* Insert a new shared policy into the list. */
-/* Caller holds sp->lock */
+/*
+ * Insert a new shared policy into the list. Caller holds sp->lock for
+ * writing.
+ */
static void sp_insert(struct shared_policy *sp, struct sp_node *new)
{
struct rb_node **p = &sp->root.rb_node;
@@ -2211,13 +2215,13 @@ mpol_shared_policy_lookup(struct shared_policy *sp, unsigned long idx)
if (!sp->root.rb_node)
return NULL;
- spin_lock(&sp->lock);
+ read_lock(&sp->lock);
sn = sp_lookup(sp, idx, idx+1);
if (sn) {
mpol_get(sn->policy);
pol = sn->policy;
}
- spin_unlock(&sp->lock);
+ read_unlock(&sp->lock);
return pol;
}
@@ -2360,7 +2364,7 @@ static int shared_policy_replace(struct shared_policy *sp, unsigned long start,
int ret = 0;
restart:
- spin_lock(&sp->lock);
+ write_lock(&sp->lock);
n = sp_lookup(sp, start, end);
/* Take care of old policies in the same range. */
while (n && n->start < end) {
@@ -2393,7 +2397,7 @@ restart:
}
if (new)
sp_insert(sp, new);
- spin_unlock(&sp->lock);
+ write_unlock(&sp->lock);
ret = 0;
err_out:
@@ -2405,7 +2409,7 @@ err_out:
return ret;
alloc_new:
- spin_unlock(&sp->lock);
+ write_unlock(&sp->lock);
ret = -ENOMEM;
n_new = kmem_cache_alloc(sn_cache, GFP_KERNEL);
if (!n_new)
@@ -2431,7 +2435,7 @@ void mpol_shared_policy_init(struct shared_policy *sp, struct mempolicy *mpol)
int ret;
sp->root = RB_ROOT; /* empty tree == default mempolicy */
- spin_lock_init(&sp->lock);
+ rwlock_init(&sp->lock);
if (mpol) {
struct vm_area_struct pvma;
@@ -2497,14 +2501,14 @@ void mpol_free_shared_policy(struct shared_policy *p)
if (!p->root.rb_node)
return;
- spin_lock(&p->lock);
+ write_lock(&p->lock);
next = rb_first(&p->root);
while (next) {
n = rb_entry(next, struct sp_node, nd);
next = rb_next(&n->nd);
sp_delete(p, n);
}
- spin_unlock(&p->lock);
+ write_unlock(&p->lock);
}
#ifdef CONFIG_NUMA_BALANCING