Revision 4df910620bebb5cfe234af16ac8f6474b60215fd authored by Feng Tang on 25 November 2020, 05:22:21 UTC, committed by Linus Torvalds on 26 November 2020, 17:35:49 UTC
0day reported one -22.7% regression for will-it-scale page_fault2
case [1] on a 4 sockets 144 CPU platform, and bisected to it to be
caused by Waiman's optimization (commit bd0b230fe1) of saving one
'struct page_counter' space for 'struct mem_cgroup'.
Initially we thought it was due to the cache alignment change introduced
by the patch, but further debug shows that it is due to some hot data
members ('vmstats_local', 'vmstats_percpu', 'vmstats') sit in 2 adjacent
cacheline (2N and 2N+1 cacheline), and when adjacent cache line prefetch
is enabled, it triggers an "extended level" of cache false sharing for
2 adjacent cache lines.
So exchange the 2 member blocks, while keeping mostly the original
cache alignment, which can restore and even enhance the performance,
and save 64 bytes of space for 'struct mem_cgroup' (from 2880 to 2816,
with 0day's default RHEL-8.3 kernel config)
[1]. https://lore.kernel.org/lkml/20201102091543.GM31092@shao2-debian/
Fixes: bd0b230fe145 ("mm/memcg: unify swap and memsw page counters")
Reported-by: kernel test robot <rong.a.chen@intel.com>
Signed-off-by: Feng Tang <feng.tang@intel.com>
Acked-by: Waiman Long <longman@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent fa02fcd
| File | Mode | Size |
|---|---|---|
| 6lowpan_i.h | -rw-r--r-- | 989 bytes |
| Kconfig | -rw-r--r-- | 2.6 KB |
| Makefile | -rw-r--r-- | 866 bytes |
| core.c | -rw-r--r-- | 4.0 KB |
| debugfs.c | -rw-r--r-- | 6.7 KB |
| iphc.c | -rw-r--r-- | 36.7 KB |
| ndisc.c | -rw-r--r-- | 6.3 KB |
| nhc.c | -rw-r--r-- | 5.1 KB |
| nhc.h | -rw-r--r-- | 4.3 KB |
| nhc_dest.c | -rw-r--r-- | 650 bytes |
| nhc_fragment.c | -rw-r--r-- | 658 bytes |
| nhc_ghc_ext_dest.c | -rw-r--r-- | 670 bytes |
| nhc_ghc_ext_frag.c | -rw-r--r-- | 682 bytes |
| nhc_ghc_ext_hop.c | -rw-r--r-- | 658 bytes |
| nhc_ghc_ext_route.c | -rw-r--r-- | 675 bytes |
| nhc_ghc_icmpv6.c | -rw-r--r-- | 613 bytes |
| nhc_ghc_udp.c | -rw-r--r-- | 571 bytes |
| nhc_hop.c | -rw-r--r-- | 633 bytes |
| nhc_ipv6.c | -rw-r--r-- | 597 bytes |
| nhc_mobility.c | -rw-r--r-- | 658 bytes |
| nhc_routing.c | -rw-r--r-- | 645 bytes |
| nhc_udp.c | -rw-r--r-- | 5.5 KB |
Computing file changes ...
