[PATCH v5 0/9] memcg: per cgroup dirty page accounting

From: Greg Thelen
Date: Fri Feb 25 2011 - 16:38:13 EST

Changes since v4:
- Moved documentation changes to start of series to provide a better
introduction to the series.
- Added support for hierarchical dirty limits.
- Incorporated bug fixes previously found in v4.
- Include a new patch "writeback: convert variables to unsigned" to provide a
clearer transition to the the new dirty_info structure (patch "writeback:
create dirty_info structure").
- Within the new dirty_info structure, replaced nr_reclaimable with
nr_file_dirty and nr_unstable_nfs to give callers finer grain dirty usage
information also added dirty_info_reclaimable().
- Rebased the series to mmotm-2011-02-10-16-26 with two pending mmotm patches:
memcg: break out event counters from other stats
memcg: use native word page statistics counters

Changes since v3:
- Refactored balance_dirty_pages() dirtying checking to use new struct
dirty_info, which is used to compare both system and memcg dirty limits
against usage.
- Disabled memcg dirty limits when memory.use_hierarchy=1. An enhancement is
needed to check the chain of parents to ensure that no dirty limit is
- Ported to mmotm-2010-10-22-16-36.

Changes since v2:
- Rather than disabling softirq in lock_page_cgroup(), introduce a separate lock
to synchronize between memcg page accounting and migration. This only affects
patch 4 of the series. Patch 4 used to disable softirq, now it introduces the
new lock.

Changes since v1:
- Renamed "nfs"/"total_nfs" to "nfs_unstable"/"total_nfs_unstable" in per cgroup
memory.stat to match /proc/meminfo.
- Avoid lockdep warnings by using rcu_read_[un]lock() in
- Fixed lockdep issue in mem_cgroup_read_stat() which is exposed by these
- Remove redundant comments.
- Rename (for clarity):
- mem_cgroup_write_page_stat_item -> mem_cgroup_page_stat_item
- mem_cgroup_read_page_stat_item -> mem_cgroup_nr_pages_item
- Renamed newly created proc files:
- memory.dirty_bytes -> memory.dirty_limit_in_bytes
- memory.dirty_background_bytes -> memory.dirty_background_limit_in_bytes
- Removed unnecessary get_ prefix from get_xxx() functions.
- Allow [kKmMgG] suffixes for newly created dirty limit value cgroupfs files.
- Disable softirq rather than hardirq in lock_page_cgroup()
- Made mem_cgroup_move_account_page_stat() inline.
- Ported patches to mmotm-2010-10-13-17-13.

This patch set provides the ability for each cgroup to have independent dirty
page limits.

Limiting dirty memory is like fixing the max amount of dirty (hard to reclaim)
page cache used by a cgroup. So, in case of multiple cgroup writers, they will
not be able to consume more than their designated share of dirty pages and will
be throttled if they cross that limit.

Example use case:
# Here is a test script that shows a situation where memcg dirty limits are
# beneficial.
# The script runs two programs:
# 1) a dirty page background antagonist (dd)
# 2) an interactive foreground process (tar).
# If the script's argument is false, then both processes are limited by the
# classic global dirty limits. If the script is given a true argument, then a
# per-cgroup dirty limit is used to contain dd dirty page consumption. The
# cgroup isolates the dd dirty memory consumption from the rest of the system
# processes (tar in this case).
# The time used by the tar process is printed (lower is better).
# When dd is run within a dirty limiting cgroup, the tar process had faster
# and more predictable performance. memcg dirty ratios might be useful to
# serve different task classes (interactive vs batch). A past discussion
# touched on this: http://lkml.org/lkml/2010/5/20/136
# When called with 'false' (using memcg without dirty isolation):
# tar finished in 7.0s
# dd reports 92 MB/s
# When called with 'true' (using memcg for dirty isolation):
# tar finished in 2.5s
# dd reports 82 MB/s

echo memcg_dirty_limits: $1

# set system dirty limits.
echo $((1<<30)) > /proc/sys/vm/dirty_bytes
echo $((1<<29)) > /proc/sys/vm/dirty_background_bytes

mkdir /dev/cgroup/memory/A

if $1; then # if using cgroup to contain 'dd'...
echo 100M > /dev/cgroup/memory/A/memory.dirty_limit_in_bytes

# run antagonist (dd) in cgroup A
(echo $BASHPID > /dev/cgroup/memory/A/tasks; \
dd if=/dev/zero of=/disk1/big.file count=10k bs=1M) &

# let antagonist (dd) get warmed up
sleep 10

# time interactive job
time tar -C /disk2 -xzf linux.tar.gz

sleep 10
rmdir /dev/cgroup/memory/A

The patches are based on a series proposed by Andrea Righi in Mar 2010.

- Add page_cgroup flags to record when pages are dirty, in writeback, or nfs

- Extend mem_cgroup to record the total number of pages in each of the
interesting dirty states (dirty, writeback, unstable_nfs).

- Add dirty parameters similar to the system-wide /proc/sys/vm/dirty_* limits to
mem_cgroup. The mem_cgroup dirty parameters are accessible via cgroupfs
control files.

- Consider both system and per-memcg dirty limits in page writeback when
deciding to queue background writeback or throttle dirty memory production.

Known shortcomings (see the patch 1 update to Documentation/cgroups/memory.txt
for more details):
- When a cgroup dirty limit is exceeded, then bdi writeback is employed to
writeback dirty inodes. Bdi writeback considers inodes from any cgroup, not
just inodes contributing dirty pages to the cgroup exceeding its limit.

- A cgroup may exceed its dirty limit if the memory is dirtied by a process in a
different memcg.

Performance data:
- A page fault microbenchmark workload was used to measure performance, which
can be called in read or write mode:
f = open(foo. $cpu)
truncate(f, 4096)
while (1) {
p = mmap(f, 4096)
if (write)
*p = 1
x = *p

- The workload was called for several points in the patch series in different
- s_read is a single threaded reader
- s_write is a single threaded writer
- p_read is a 16 thread reader, each operating on a different file
- p_write is a 16 thread writer, each operating on a different file

- Measurements were collected on a 16 core non-numa system using "perf stat
--repeat 3".

- All numbers are page fault rate (M/sec). Higher is better.

- To compare the performance of a kernel without memcg compare the first and
last rows - neither has memcg configured. The first row does not include any
of these memcg dirty limit patches.

- To compare the performance of using memcg dirty limits, compare the memcg
baseline (2nd row titled "mmotm w/ memcg") with the 3rd row (memcg enabled
with all patches).

root_cgroup child_cgroup
s_read s_write p_read p_write s_read s_write p_read p_write
mmotm w/o memcg 0.359 0.312 0.357 0.312
mmotm w/ memcg 0.366 0.316 0.342 0.301 0.368 0.309 0.347 0.301
all patches 0.347 0.322 0.327 0.303 0.342 0.323 0.327 0.305
all patches 0.358 0.322 0.357 0.316
w/o memcg

Greg Thelen (9):
memcg: document cgroup dirty memory interfaces
memcg: add page_cgroup flags for dirty page tracking
writeback: convert variables to unsigned
writeback: create dirty_info structure
memcg: add dirty page accounting infrastructure
memcg: add kernel calls for memcg dirty page stats
memcg: add dirty limits to mem_cgroup
memcg: add cgroupfs interface to memcg dirty limits
memcg: check memcg dirty limits in page writeback

Documentation/cgroups/memory.txt | 80 +++++++
fs/fs-writeback.c | 7 +-
fs/nfs/write.c | 4 +
include/linux/memcontrol.h | 33 +++-
include/linux/page_cgroup.h | 23 ++
include/linux/writeback.h | 18 ++-
mm/backing-dev.c | 18 +-
mm/filemap.c | 1 +
mm/memcontrol.c | 470 +++++++++++++++++++++++++++++++++++++-
mm/page-writeback.c | 150 +++++++++----
mm/truncate.c | 1 +
mm/vmscan.c | 2 +-
mm/vmstat.c | 6 +-
13 files changed, 742 insertions(+), 71 deletions(-)


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