AcoSail/kernel_optimize_test
8
0
Fork 0
forked from luck/tmp_suning_uos_patched
Code Pull Requests Activity
840,942 Commits 7 Branches 0 Tags 1.9 GiB
C 98%
Assembly 1.1%
Shell 0.3%
Makefile 0.3%
Python 0.1%
Other 0.1%
815744d751
Go to file
Johannes Weiner 815744d751 mm: memcontrol: don't batch updates of local VM stats and events 
The kernel test robot noticed a 26% will-it-scale pagefault regression
from commit 42a3003535 ("mm: memcontrol: fix recursive statistics
correctness & scalabilty").  This appears to be caused by bouncing the
additional cachelines from the new hierarchical statistics counters.

We can fix this by getting rid of the batched local counters instead.

Originally, there were *only* group-local counters, and they were fully
maintained per cpu.  A reader of a stats file high up in the cgroup tree
would have to walk the entire subtree and collect each level's per-cpu
counters to get the recursive view.  This was prohibitively expensive,
and so we switched to per-cpu batched updates of the local counters
during a983b5ebee ("mm: memcontrol: fix excessive complexity in
memory.stat reporting"), reducing the complexity from nr_subgroups *
nr_cpus to nr_subgroups.

With growing machines and cgroup trees, the tree walk itself became too
expensive for monitoring top-level groups, and this is when the culprit
patch added hierarchy counters on each cgroup level.  When the per-cpu
batch size would be reached, both the local and the hierarchy counters
would get batch-updated from the per-cpu delta simultaneously.

This makes local and hierarchical counter reads blazingly fast, but it
unfortunately makes the write-side too cache line intense.

Since local counter reads were never a problem - we only centralized
them to accelerate the hierarchy walk - and use of the local counters
are becoming rarer due to replacement with hierarchical views (ongoing
rework in the page reclaim and workingset code), we can make those local
counters unbatched per-cpu counters again.

The scheme will then be as such:

   when a memcg statistic changes, the writer will:
   - update the local counter (per-cpu)
   - update the batch counter (per-cpu). If the batch is full:
   - spill the batch into the group's atomic_t
   - spill the batch into all ancestors' atomic_ts
   - empty out the batch counter (per-cpu)

   when a local memcg counter is read, the reader will:
   - collect the local counter from all cpus

   when a hiearchy memcg counter is read, the reader will:
   - read the atomic_t

We might be able to simplify this further and make the recursive
counters unbatched per-cpu counters as well (batch upward propagation,
but leave per-cpu collection to the readers), but that will require a
more in-depth analysis and testing of all the callsites.  Deal with the
immediate regression for now.

Link: http://lkml.kernel.org/r/20190521151647.GB2870@cmpxchg.org
Fixes: 42a3003535 ("mm: memcontrol: fix recursive statistics correctness & scalabilty")
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reported-by: kernel test robot <rong.a.chen@intel.com>
Tested-by: kernel test robot <rong.a.chen@intel.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Roman Gushchin <guro@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-06-13 17:34:56 -10:00
arch s390 updates for 5.2-rc4 2019-06-08 13:12:54 -07:00
block cgroup/bfq: revert bfq.weight symlink change 2019-06-10 03:35:41 -06:00
certs
crypto SPDX update for 5.2-rc4 2019-06-08 12:52:42 -07:00
Documentation
drivers Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/hid/hid 2019-06-13 05:59:05 -10:00
fs for-5.2-rc4-tag 2019-06-11 15:10:15 -10:00
include mm: memcontrol: don't batch updates of local VM stats and events 2019-06-13 17:34:56 -10:00
init Char/Misc driver fixes for 5.2-rc4 2019-06-08 12:50:36 -07:00
ipc
kernel Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2019-06-11 15:44:45 -10:00
lib SPDX update for 5.2-rc4 2019-06-08 12:52:42 -07:00
LICENSES
mm mm: memcontrol: don't batch updates of local VM stats and events 2019-06-13 17:34:56 -10:00
net SPDX update for 5.2-rc4 2019-06-08 12:52:42 -07:00
samples SPDX update for 5.2-rc4 2019-06-08 12:52:42 -07:00
scripts SPDX update for 5.2-rc4 2019-06-08 12:52:42 -07:00
security selinux/stable-5.2 PR 20190612 2019-06-12 16:10:57 -10:00
sound
tools SPDX update for 5.2-rc4 2019-06-08 12:52:42 -07:00
usr
virt
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
.mailmap
COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS
Makefile Linux 5.2-rc4 2019-06-08 20:24:46 -07:00
README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.