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Date: Thu, 16 Jan 2014 18:17:01 -0500
From: Debabrata Banerjee <dbanerje@...mai.com>
To: eric.dumazet@...il.com, fw@...len.de, netdev@...r.kernel.org
Cc: dbanerje@...mai.com, johunt@...mai.com, jbaron@...mai.com,
davem@...emloft.net, linux-mm@...ck.org
Subject: [RFC PATCH 0/3] Use cached allocations in place of order-3 allocations for sk_page_frag_refill() and __netdev_alloc_frag()
This is a hack against 3.10.y to see if using cached allocations works better here. The unintended consequence is in the reference benchmark case, it performs ~7% better than the existing code even with a hacked slower get_page()/put_page(). The intent was to avoid very slow order-3 allocations (and really pathological retries under failure) which can cause lots of problems from OOM killer invocation to direct reclaim/compaction cycles that take up nearly all cpu and end up reaping large amounts of page cache which would have been otherwise useful. This is a regression from the same code that used order-0 allocations since those are easy and fast as they are cached per-cpu, and this code is under very heavy alloc/free behavior. This patch eliminates a majority of that due to slab caching the allocations, though could still be improved by slab holding onto free'd slabs longer; this seems like an unoptimized case when object size == slab size.
vmstat output of bad behavior: http://pastebin.ubuntu.com/6687527/
This patchset could be fixed for submission by either making another pool of cached frag buffers specifically page_frag (not using slab), or by converting the whole stack to not use get_page/put_page() to reference count and free page allocations so that hacking swap.c is not necessary and slab use normal.
Benchmark:
ifconfig lo mtu 16436
perf record ./netperf -t UDP_STREAM ; perf report
With order-0 allocations:
UDP UNIDIRECTIONAL SEND TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to localhost (127.0.0.1) port 0 AF_INET
Socket Message Elapsed Messages
Size Size Time Okay Errors Throughput
bytes bytes secs # # 10^6bits/sec
262144 65507 10.00 820758 0 43012.26
262144 10.00 820754 43012.05
# Overhead Command Shared Object Symbol
# ........ ....... ................. ..........................................
#
46.15% netperf [kernel.kallsyms] [k] copy_user_generic_string
7.89% netperf [kernel.kallsyms] [k] skb_append_datato_frags
6.06% netperf [kernel.kallsyms] [k] get_page_from_freelist
3.87% netperf [kernel.kallsyms] [k] __rmqueue
1.36% netperf [kernel.kallsyms] [k] __alloc_pages_nodemask
1.11% netperf [kernel.kallsyms] [k] alloc_pages_current
linux-3.10.y stock order-3 allocations:
UDP UNIDIRECTIONAL SEND TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to localhost (127.0.0.1) port 0 AF_INET
Socket Message Elapsed Messages
Size Size Time Okay Errors Throughput
bytes bytes secs # # 10^6bits/sec
212992 65507 10.00 1054158 0 55243.69
212992 10.00 1019505 53427.68
# Overhead Command Shared Object Symbol
# ........ ....... ................. ..........................................
#
59.80% netperf [kernel.kallsyms] [k] copy_user_generic_string
2.35% netperf [kernel.kallsyms] [k] get_page_from_freelist
1.95% netperf [kernel.kallsyms] [k] skb_append_datato_frags
1.27% netperf [ip_tables] [k] ipt_do_table
1.26% netperf [kernel.kallsyms] [k] udp_sendmsg
1.03% netperf [kernel.kallsyms] [k] enqueue_task_fair
1.00% netperf [kernel.kallsyms] [k] ip_finish_output
With this patchset:
UDP UNIDIRECTIONAL SEND TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to localhost (127.0.0.1) port 0 AF_INET
Socket Message Elapsed Messages
Size Size Time Okay Errors Throughput
bytes bytes secs # # 10^6bits/sec
212992 65507 10.00 1127089 0 59065.70
212992 10.00 1072997 56230.98
# Overhead Command Shared Object Symbol
# ........ ....... ................. ..........................................
#
69.16% netperf [kernel.kallsyms] [k] copy_user_generic_string
2.56% netperf [kernel.kallsyms] [k] skb_append_datato_frags
1.00% netperf [ip_tables] [k] ipt_do_table
0.96% netperf [kernel.kallsyms] [k] sock_alloc_send_pskb
0.93% netperf [kernel.kallsyms] [k] _raw_spin_lock
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