Commits
Florian Westphal committed 4cf0b354d92
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 [..]
[<ffffffff811633ed>] warn_alloc_failed+0xdd/0x140
[<ffffffff811638b1>] __alloc_pages_nodemask+0x3e1/0xcf0
[<ffffffff811a72ed>] alloc_pages_current+0x8d/0x110
[<ffffffff8117cb7f>] kmalloc_order+0x1f/0x70
[<ffffffff811aec19>] __kmalloc+0x129/0x140
[<ffffffff8146d561>] bucket_table_alloc+0xc1/0x1d0
[<ffffffff8146da1d>] rhashtable_insert_rehash+0x5d/0xe0
[<ffffffff819fcfff>] 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 <linux@eikelenboom.it>
Suggested-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>