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authorNathan Zimmer <nzimmer@sgi.com>2016-01-14 15:18:36 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2016-01-14 16:00:49 -0800
commit4a8c7bb59ac85b038c29adf6d32ff56e11fbb267 (patch)
tree76ded28807d90dab68c27f1d33412209be004d27 /fs/hugetlbfs
parent8f235d1a3eb7198affe7cadf676a10afb8a46a1a (diff)
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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 'fs/hugetlbfs')
-rw-r--r--fs/hugetlbfs/inode.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index f6820ecf0a11..a1cb8fd2289b 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -738,7 +738,7 @@ static struct inode *hugetlbfs_get_inode(struct super_block *sb,
/*
* The policy is initialized here even if we are creating a
* private inode because initialization simply creates an
- * an empty rb tree and calls spin_lock_init(), later when we
+ * an empty rb tree and calls rwlock_init(), later when we
* call mpol_free_shared_policy() it will just return because
* the rb tree will still be empty.
*/