# git rev-parse -q --verify 4df910620bebb5cfe234af16ac8f6474b60215fd^{commit}
4df910620bebb5cfe234af16ac8f6474b60215fd
already have revision, skipping fetch
# git checkout -q -f -B kisskb 4df910620bebb5cfe234af16ac8f6474b60215fd
# git clean -qxdf
# < git log -1
# commit 4df910620bebb5cfe234af16ac8f6474b60215fd
# Author: Feng Tang <feng.tang@intel.com>
# Date:   Wed Nov 25 13:22:21 2020 +0800
# 
#     mm: memcg: relayout structure mem_cgroup to avoid cache interference
#     
#     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>
# < /opt/cross/kisskb/korg/gcc-4.9.4-nolibc/ia64-linux/bin/ia64-linux-gcc --version
# < /opt/cross/kisskb/korg/gcc-4.9.4-nolibc/ia64-linux/bin/ia64-linux-ld --version
# < git log --format=%s --max-count=1 4df910620bebb5cfe234af16ac8f6474b60215fd
# < make -s -j 80 ARCH=ia64 O=/kisskb/build/linus_ia64-defconfig_ia64-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/ia64-linux/bin/ia64-linux-  defconfig
arch/ia64/configs/generic_defconfig:58:warning: override: reassigning to symbol ATA
arch/ia64/configs/generic_defconfig:59:warning: override: reassigning to symbol ATA_PIIX
# < make -s -j 80 ARCH=ia64 O=/kisskb/build/linus_ia64-defconfig_ia64-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/ia64-linux/bin/ia64-linux-  help
# make -s -j 80 ARCH=ia64 O=/kisskb/build/linus_ia64-defconfig_ia64-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/ia64-linux/bin/ia64-linux-  olddefconfig
# make -s -j 80 ARCH=ia64 O=/kisskb/build/linus_ia64-defconfig_ia64-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/ia64-linux/bin/ia64-linux-  
<stdin>:1511:2: warning: #warning syscall clone3 not implemented [-Wcpp]
In file included from /kisskb/src/arch/ia64/include/uapi/asm/intrinsics.h:22:0,
                 from /kisskb/src/arch/ia64/include/asm/intrinsics.h:11,
                 from /kisskb/src/arch/ia64/include/asm/timex.h:14,
                 from /kisskb/src/include/linux/timex.h:65,
                 from /kisskb/src/include/linux/time32.h:13,
                 from /kisskb/src/include/linux/time.h:73,
                 from /kisskb/src/fs/nfs/read.c:11:
/kisskb/src/fs/nfs/read.c: In function 'nfs_read_completion':
/kisskb/src/arch/ia64/include/uapi/asm/cmpxchg.h:57:2: warning: value computed is not used [-Wunused-value]
 ((__typeof__(*(ptr))) __xchg((unsigned long) (x), (ptr), sizeof(*(ptr))))
  ^
/kisskb/src/fs/nfs/read.c:196:5: note: in expansion of macro 'xchg'
     xchg(&nfs_req_openctx(req)->error, error);
     ^
/kisskb/src/fs/nfs/read.c: In function 'nfs_readpage':
/kisskb/src/arch/ia64/include/uapi/asm/cmpxchg.h:57:2: warning: value computed is not used [-Wunused-value]
 ((__typeof__(*(ptr))) __xchg((unsigned long) (x), (ptr), sizeof(*(ptr))))
  ^
/kisskb/src/fs/nfs/read.c:355:2: note: in expansion of macro 'xchg'
  xchg(&ctx->error, 0);
  ^
No errors detected in 22333 functions.
Completed OK
# rm -rf /kisskb/build/linus_ia64-defconfig_ia64-gcc4.9
# Build took: 0:02:25.441462