[PATCH 00/27] Move LRU page reclaim from zones to nodes v7

From: Mel Gorman
Date: Tue Jun 21 2016 - 07:53:04 EST

The bulk of the updates are in response to review from Vlastimil Babka
and received a lot more testing than v6.

Changelog since v6
o Correct reclaim_idx when direct reclaiming for memcg
o Also account LRU pages per zone for compaction/reclaim
o Add page_pgdat helper with more efficient lookup
o Init pgdat LRU lock only once
o Slight optimisation to wake_all_kswapds
o Always wake kcompactd when kswapd is going to sleep
o Rebase to mmotm as of June 15th, 2016

Changelog since v5
o Rebase and adjust to changes

Changelog since v4
o Rebase on top of v3 of page allocator optimisation series

Changelog since v3
o Rebase on top of the page allocator optimisation series
o Remove RFC tag

This is the latest version of a series that moves LRUs from the zones to
the node that is based upon 4.6-rc3 plus the page allocator optimisation
series. Conceptually, this is simple but there are a lot of details. Some
of the broad motivations for this are;

1. The residency of a page partially depends on what zone the page was
allocated from. This is partially combatted by the fair zone allocation
policy but that is a partial solution that introduces overhead in the
page allocator paths.

2. Currently, reclaim on node 0 behaves slightly different to node 1. For
example, direct reclaim scans in zonelist order and reclaims even if
the zone is over the high watermark regardless of the age of pages
in that LRU. Kswapd on the other hand starts reclaim on the highest
unbalanced zone. A difference in distribution of file/anon pages due
to when they were allocated results can result in a difference in
again. While the fair zone allocation policy mitigates some of the
problems here, the page reclaim results on a multi-zone node will
always be different to a single-zone node.
it was scheduled on as a result.

3. kswapd and the page allocator scan zones in the opposite order to
avoid interfering with each other but it's sensitive to timing. This
mitigates the page allocator using pages that were allocated very recently
in the ideal case but it's sensitive to timing. When kswapd is allocating
from lower zones then it's great but during the rebalancing of the highest
zone, the page allocator and kswapd interfere with each other. It's worse
if the highest zone is small and difficult to balance.

4. slab shrinkers are node-based which makes it harder to identify the exact
relationship between slab reclaim and LRU reclaim.

The reason we have zone-based reclaim is that we used to have
large highmem zones in common configurations and it was necessary
to quickly find ZONE_NORMAL pages for reclaim. Today, this is much
less of a concern as machines with lots of memory will (or should) use
64-bit kernels. Combinations of 32-bit hardware and 64-bit hardware are
rare. Machines that do use highmem should have relatively low highmem:lowmem
ratios than we worried about in the past.

Conceptually, moving to node LRUs should be easier to understand. The
page allocator plays fewer tricks to game reclaim and reclaim behaves
similarly on all nodes.

The series has been tested on a 16 core UMA machine and a 2-socket 48 core
NUMA machine. The UMA results are presented in most cases as the NUMA machine
behaved similarly.

pagealloc
---------

This is a microbenchmark that shows the benefit of removing the fair zone
allocation policy. It was tested uip to order-4 but only orders 0 and 1 are
shown as the other orders were comparable.

4.7.0-rc3 4.7.0-rc3
mmotm-20160615 nodelru-v7r17
Min total-odr0-1 485.00 ( 0.00%) 462.00 ( 4.74%)
Min total-odr0-2 354.00 ( 0.00%) 341.00 ( 3.67%)
Min total-odr0-4 285.00 ( 0.00%) 277.00 ( 2.81%)
Min total-odr0-8 249.00 ( 0.00%) 240.00 ( 3.61%)
Min total-odr0-16 230.00 ( 0.00%) 224.00 ( 2.61%)
Min total-odr0-32 222.00 ( 0.00%) 215.00 ( 3.15%)
Min total-odr0-64 216.00 ( 0.00%) 210.00 ( 2.78%)
Min total-odr0-128 214.00 ( 0.00%) 208.00 ( 2.80%)
Min total-odr0-256 248.00 ( 0.00%) 233.00 ( 6.05%)
Min total-odr0-512 277.00 ( 0.00%) 270.00 ( 2.53%)
Min total-odr0-1024 294.00 ( 0.00%) 284.00 ( 3.40%)
Min total-odr0-2048 308.00 ( 0.00%) 298.00 ( 3.25%)
Min total-odr0-4096 318.00 ( 0.00%) 307.00 ( 3.46%)
Min total-odr0-8192 322.00 ( 0.00%) 308.00 ( 4.35%)
Min total-odr0-16384 324.00 ( 0.00%) 309.00 ( 4.63%)
Min total-odr1-1 729.00 ( 0.00%) 686.00 ( 5.90%)
Min total-odr1-2 533.00 ( 0.00%) 520.00 ( 2.44%)
Min total-odr1-4 434.00 ( 0.00%) 415.00 ( 4.38%)
Min total-odr1-8 390.00 ( 0.00%) 364.00 ( 6.67%)
Min total-odr1-16 359.00 ( 0.00%) 335.00 ( 6.69%)
Min total-odr1-32 356.00 ( 0.00%) 327.00 ( 8.15%)
Min total-odr1-64 356.00 ( 0.00%) 321.00 ( 9.83%)
Min total-odr1-128 356.00 ( 0.00%) 333.00 ( 6.46%)
Min total-odr1-256 354.00 ( 0.00%) 337.00 ( 4.80%)
Min total-odr1-512 366.00 ( 0.00%) 340.00 ( 7.10%)
Min total-odr1-1024 373.00 ( 0.00%) 354.00 ( 5.09%)
Min total-odr1-2048 375.00 ( 0.00%) 354.00 ( 5.60%)
Min total-odr1-4096 374.00 ( 0.00%) 354.00 ( 5.35%)
Min total-odr1-8192 370.00 ( 0.00%) 355.00 ( 4.05%)

This shows a steady improvement throughout. The primary benefit is from
reduced system CPU usage which is obvious from the overall times;

4.7.0-rc3 4.7.0-rc3
mmotm-20160615 nodelru-v7
User 174.06 174.58
System 2656.78 2485.21
Elapsed 2885.07 2713.67

The vmstats also showed that the fair zone allocation policy was definitely
removed as can be seen here;

4.7.0-rc3 4.7.0-rc3
mmotm-20160615nodelru-v7r17
DMA32 allocs 28794408561 0
Normal allocs 48431969998 77226313470
Movable allocs 0 0

tiobench on ext4
----------------

tiobench is a benchmark that artifically benefits if old pages remain resident
while new pages get reclaimed. The fair zone allocation policy mitigates this
problem so pages age fairly. While the benchmark has problems, it is important
that tiobench performance remains constant as it implies that page aging
problems that the fair zone allocation policy fixes are not re-introduced.

4.7.0-rc3 4.7.0-rc3
mmotm-20160615 nodelru-v7r17
Min PotentialReadSpeed 90.24 ( 0.00%) 90.14 ( -0.11%)
Min SeqRead-MB/sec-1 80.63 ( 0.00%) 83.09 ( 3.05%)
Min SeqRead-MB/sec-2 71.91 ( 0.00%) 72.44 ( 0.74%)
Min SeqRead-MB/sec-4 75.20 ( 0.00%) 74.32 ( -1.17%)
Min SeqRead-MB/sec-8 65.30 ( 0.00%) 65.21 ( -0.14%)
Min SeqRead-MB/sec-16 62.62 ( 0.00%) 62.12 ( -0.80%)
Min RandRead-MB/sec-1 0.90 ( 0.00%) 0.94 ( 4.44%)
Min RandRead-MB/sec-2 0.96 ( 0.00%) 0.97 ( 1.04%)
Min RandRead-MB/sec-4 1.43 ( 0.00%) 1.41 ( -1.40%)
Min RandRead-MB/sec-8 1.67 ( 0.00%) 1.72 ( 2.99%)
Min RandRead-MB/sec-16 1.77 ( 0.00%) 1.86 ( 5.08%)
Min SeqWrite-MB/sec-1 78.12 ( 0.00%) 79.78 ( 2.12%)
Min SeqWrite-MB/sec-2 72.74 ( 0.00%) 73.23 ( 0.67%)
Min SeqWrite-MB/sec-4 79.40 ( 0.00%) 78.32 ( -1.36%)
Min SeqWrite-MB/sec-8 73.18 ( 0.00%) 71.40 ( -2.43%)
Min SeqWrite-MB/sec-16 75.82 ( 0.00%) 75.24 ( -0.76%)
Min RandWrite-MB/sec-1 1.18 ( 0.00%) 1.15 ( -2.54%)
Min RandWrite-MB/sec-2 1.05 ( 0.00%) 0.99 ( -5.71%)
Min RandWrite-MB/sec-4 1.00 ( 0.00%) 0.96 ( -4.00%)
Min RandWrite-MB/sec-8 0.91 ( 0.00%) 0.92 ( 1.10%)
Min RandWrite-MB/sec-16 0.92 ( 0.00%) 0.92 ( 0.00%)

This shows that the series has little or not impact on tiobench which is
desirable. It indicates that the fair zone allocation policy was removed
in a manner that didn't reintroduce one class of page aging bug. There
were only minor differences in overall reclaim activity

4.7.0-rc3 4.7.0-rc3
mmotm-20160615nodelru-v7r17
Minor Faults 640992 640721
Major Faults 728 623
Swap Ins 0 0
Swap Outs 0 0
DMA allocs 0 0
DMA32 allocs 46174282 44219717
Normal allocs 77949344 79858024
Movable allocs 0 0
Allocation stalls 38 76
Direct pages scanned 17463 34865
Kswapd pages scanned 93331163 93302388
Kswapd pages reclaimed 93328173 93299677
Direct pages reclaimed 17463 34865
Kswapd efficiency 99% 99%
Kswapd velocity 13729.855 13755.612
Direct efficiency 100% 100%
Direct velocity 2.569 5.140
Percentage direct scans 0% 0%
Page writes by reclaim 0 0
Page writes file 0 0
Page writes anon 0 0
Page reclaim immediate 54 36

kswapd activity was roughly comparable. There was slight differences
in direct reclaim activity but negligible in the context of the overall
workload (velocity of 5 pages per second with the patches applied, 2 pages
per second in the baseline kernel).

pgbench read-only large configuration on ext4
---------------------------------------------

pgbench is a database benchmark that can be sensitive to page reclaim
decisions. This also checks if removing the fair zone allocation policy
is safe

pgbench Transactions
4.7.0-rc3 4.7.0-rc3
mmotm-20160615 nodelru-v7r17
Hmean 1 191.00 ( 0.00%) 193.67 ( 1.40%)
Hmean 5 338.59 ( 0.00%) 336.99 ( -0.47%)
Hmean 12 374.03 ( 0.00%) 386.15 ( 3.24%)
Hmean 21 372.24 ( 0.00%) 372.02 ( -0.06%)
Hmean 30 383.98 ( 0.00%) 370.69 ( -3.46%)
Hmean 32 431.01 ( 0.00%) 438.47 ( 1.73%)

Negligible differences again. As with tiobench, overall reclaim activity
was comparable.

bonnie++ on ext4
----------------

No interesting performance difference, negligible differences on reclaim
stats.

paralleldd on ext4
------------------

This workload uses varying numbers of dd instances to read large amounts of
data from disk.

paralleldd
4.7.0-rc3 4.7.0-rc3
mmotm-20160615 nodelru-v7r17
Amean Elapsd-1 181.57 ( 0.00%) 179.63 ( 1.07%)
Amean Elapsd-3 188.29 ( 0.00%) 183.68 ( 2.45%)
Amean Elapsd-5 188.02 ( 0.00%) 181.73 ( 3.35%)
Amean Elapsd-7 186.07 ( 0.00%) 184.11 ( 1.05%)
Amean Elapsd-12 188.16 ( 0.00%) 183.51 ( 2.47%)
Amean Elapsd-16 189.03 ( 0.00%) 181.27 ( 4.10%)

4.7.0-rc3 4.7.0-rc3
mmotm-20160615nodelru-v7r17
User 1439.23 1433.37
System 8332.31 8216.01
Elapsed 3619.80 3532.69

There is a slight gain in performance, some of which is from the reduced system
CPU usage. There areminor differences in reclaim activity but nothing significant

4.7.0-rc3 4.7.0-rc3
mmotm-20160615nodelru-v7r17
Minor Faults 362486 358215
Major Faults 1143 1113
Swap Ins 26 0
Swap Outs 2920 482
DMA allocs 0 0
DMA32 allocs 31568814 28598887
Normal allocs 46539922 49514444
Movable allocs 0 0
Allocation stalls 0 0
Direct pages scanned 0 0
Kswapd pages scanned 40886878 40849710
Kswapd pages reclaimed 40869923 40835207
Direct pages reclaimed 0 0
Kswapd efficiency 99% 99%
Kswapd velocity 11295.342 11563.344
Direct efficiency 100% 100%
Direct velocity 0.000 0.000
Slabs scanned 131673 126099
Direct inode steals 57 60
Kswapd inode steals 762 18

It basically shows that kswapd was active at roughly the same rate in
both kernels. There was also comparable slab scanning activity and direct
reclaim was avoided in both cases. There appears to be a large difference
in numbers of inodes reclaimed but the workload has few active inodes and
is likely a timing artifact. It's interesting to note that the node-lru
did not swap in any pages but given the low swap activity, it's unlikely
to be significant.

stutter
-------

stutter simulates a simple workload. One part uses a lot of anonymous
memory, a second measures mmap latency and a third copies a large file.
The primary metric is checking for mmap latency.

stutter
4.7.0-rc3 4.7.0-rc3
mmotm-20160615 nodelru-v7r17
Min mmap 16.8422 ( 0.00%) 15.9821 ( 5.11%)
1st-qrtle mmap 57.8709 ( 0.00%) 58.0794 ( -0.36%)
2nd-qrtle mmap 58.4335 ( 0.00%) 59.4286 ( -1.70%)
3rd-qrtle mmap 58.6957 ( 0.00%) 59.6862 ( -1.69%)
Max-90% mmap 58.9388 ( 0.00%) 59.8759 ( -1.59%)
Max-93% mmap 59.0505 ( 0.00%) 59.9333 ( -1.50%)
Max-95% mmap 59.1877 ( 0.00%) 59.9844 ( -1.35%)
Max-99% mmap 60.3237 ( 0.00%) 60.2337 ( 0.15%)
Max mmap 285.6454 ( 0.00%) 135.6006 ( 52.53%)
Mean mmap 57.8366 ( 0.00%) 58.4884 ( -1.13%)

This shows that there is a slight impact on mmap latency but that
the worst-case outlier is much improved. As the problem with this
benchmark used to be that the kernel stalled for minutes, this
difference is negligible.

Some of the vmstats are interesting

4.7.0-rc3 4.7.0-rc3
mmotm-20160615nodelru-v7r17
Swap Ins 58 42
Swap Outs 0 0
Allocation stalls 16 0
Direct pages scanned 1374 0
Kswapd pages scanned 42454910 41782544
Kswapd pages reclaimed 41571035 41781833
Direct pages reclaimed 1167 0
Kswapd efficiency 97% 99%
Kswapd velocity 14774.479 14223.796
Direct efficiency 84% 100%
Direct velocity 0.478 0.000
Percentage direct scans 0% 0%
Page writes by reclaim 696918 0
Page writes file 696918 0
Page writes anon 0 0
Page reclaim immediate 2940 137
Sector Reads 81644424 81699544
Sector Writes 99193620 98862160
Page rescued immediate 0 0
Slabs scanned 1279838 22640

kswapd and direct reclaim activity are similar but the node LRU series
did not attempt to trigger any page writes from reclaim context.

This series is not without its hazards. There are at least three areas
that I'm concerned with even though I could not reproduce any problems in
that area.

1. Reclaim/compaction is going to be affected because the amount of reclaim is
no longer targetted at a specific zone. Compaction works on a per-zone basis
so there is no guarantee that reclaiming a few THP's worth page pages will
have a positive impact on compaction success rates.

2. The Slab/LRU reclaim ratio is affected because the frequency the shrinkers
are called is now different. This may or may not be a problem but if it
is, it'll be because shrinkers are not called enough and some balancing
is required.

3. The anon/file reclaim ratio may be affected. Pages about to be dirtied are
distributed between zones and the fair zone allocation policy used to do
something very similar for anon. The distribution is now different but not
necessarily in any way that matters but it's still worth bearing in mind.

Documentation/cgroup-v1/memcg_test.txt | 4 +-
Documentation/cgroup-v1/memory.txt | 4 +-
arch/s390/appldata/appldata_mem.c | 2 +-
arch/tile/mm/pgtable.c | 18 +-
drivers/base/node.c | 73 +--
drivers/staging/android/lowmemorykiller.c | 12 +-
fs/fs-writeback.c | 4 +-
fs/fuse/file.c | 8 +-
fs/nfs/internal.h | 2 +-
fs/nfs/write.c | 2 +-
fs/proc/meminfo.c | 14 +-
include/linux/backing-dev.h | 2 +-
include/linux/memcontrol.h | 32 +-
include/linux/mm.h | 5 +
include/linux/mm_inline.h | 21 +-
include/linux/mm_types.h | 2 +-
include/linux/mmzone.h | 158 +++---
include/linux/swap.h | 23 +-
include/linux/topology.h | 2 +-
include/linux/vm_event_item.h | 14 +-
include/linux/vmstat.h | 111 +++-
include/linux/writeback.h | 2 +-
include/trace/events/vmscan.h | 63 ++-
include/trace/events/writeback.h | 10 +-
kernel/power/snapshot.c | 10 +-
kernel/sysctl.c | 4 +-
mm/backing-dev.c | 15 +-
mm/compaction.c | 28 +-
mm/filemap.c | 14 +-
mm/huge_memory.c | 33 +-
mm/internal.h | 11 +-
mm/memcontrol.c | 246 ++++----
mm/memory-failure.c | 4 +-
mm/memory_hotplug.c | 7 +-
mm/mempolicy.c | 2 +-
mm/migrate.c | 35 +-
mm/mlock.c | 12 +-
mm/page-writeback.c | 124 ++--
mm/page_alloc.c | 268 ++++-----
mm/page_idle.c | 4 +-
mm/rmap.c | 14 +-
mm/shmem.c | 12 +-
mm/swap.c | 66 +--
mm/swap_state.c | 4 +-
mm/util.c | 4 +-
mm/vmscan.c | 901 +++++++++++++++---------------
mm/vmstat.c | 376 ++++++++++---
mm/workingset.c | 54 +-
48 files changed, 1573 insertions(+), 1263 deletions(-)

--
2.6.4