From 4cf0b354d92ee2c642532ee39e330f8f580fd985 Mon Sep 17 00:00:00 2001 From: Florian Westphal Date: Fri, 12 Aug 2016 12:03:52 +0200 Subject: [PATCH] rhashtable: avoid large lock-array allocations Sander reports following splat after netfilter nat bysrc table got converted to rhashtable: swapper/0: page allocation failure: order:3, mode:0x2084020(GFP_ATOMIC|__GFP_COMP) CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.8.0-rc1 [..] [] warn_alloc_failed+0xdd/0x140 [] __alloc_pages_nodemask+0x3e1/0xcf0 [] alloc_pages_current+0x8d/0x110 [] kmalloc_order+0x1f/0x70 [] __kmalloc+0x129/0x140 [] bucket_table_alloc+0xc1/0x1d0 [] rhashtable_insert_rehash+0x5d/0xe0 [] nf_nat_setup_info+0x2ef/0x400 The failure happens when allocating the spinlock array. Even with GFP_KERNEL its unlikely for such a large allocation to succeed. Thomas Graf pointed me at inet_ehash_locks_alloc(), so in addition to adding NOWARN for atomic allocations this also makes the bucket-array sizing more conservative. In commit 095dc8e0c3686 ("tcp: fix/cleanup inet_ehash_locks_alloc()"), Eric Dumazet says: "Budget 2 cache lines per cpu worth of 'spinlocks'". IOW, consider size needed by a single spinlock when determining number of locks per cpu. So with 64 byte per cacheline and 4 byte per spinlock this gives 32 locks per cpu. Resulting size of the lock-array (sizeof(spinlock) == 4): cpus: 1 2 4 8 16 32 64 old: 1k 1k 4k 8k 16k 16k 16k new: 128 256 512 1k 2k 4k 8k 8k allocation should have decent chance of success even with GFP_ATOMIC, and should not fail with GFP_KERNEL. With 72-byte spinlock (LOCKDEP): cpus : 1 2 old: 9k 18k new: ~2k ~4k Reported-by: Sander Eikelenboom Suggested-by: Thomas Graf Signed-off-by: Florian Westphal Signed-off-by: David S. Miller --- lib/rhashtable.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/lib/rhashtable.c b/lib/rhashtable.c index 5d845ffd7982..42acd81f10db 100644 --- a/lib/rhashtable.c +++ b/lib/rhashtable.c @@ -30,7 +30,7 @@ #define HASH_DEFAULT_SIZE 64UL #define HASH_MIN_SIZE 4U -#define BUCKET_LOCKS_PER_CPU 128UL +#define BUCKET_LOCKS_PER_CPU 32UL static u32 head_hashfn(struct rhashtable *ht, const struct bucket_table *tbl, @@ -70,7 +70,7 @@ static int alloc_bucket_locks(struct rhashtable *ht, struct bucket_table *tbl, unsigned int nr_pcpus = num_possible_cpus(); #endif - nr_pcpus = min_t(unsigned int, nr_pcpus, 32UL); + nr_pcpus = min_t(unsigned int, nr_pcpus, 64UL); size = roundup_pow_of_two(nr_pcpus * ht->p.locks_mul); /* Never allocate more than 0.5 locks per bucket */ @@ -83,6 +83,9 @@ static int alloc_bucket_locks(struct rhashtable *ht, struct bucket_table *tbl, tbl->locks = vmalloc(size * sizeof(spinlock_t)); else #endif + if (gfp != GFP_KERNEL) + gfp |= __GFP_NOWARN | __GFP_NORETRY; + tbl->locks = kmalloc_array(size, sizeof(spinlock_t), gfp); if (!tbl->locks) -- 2.30.2