Previous releases double accounted LRU stats on the zone and the node
because it was required by should_reclaim_retry. The last patch in the
series removes the double accounting. It's not integrated with the series
as reviewers may not like the solution. If not, it can be safely dropped
without a major impact to the results.
Changelog since v7
o Rebase onto current mmots
o Avoid double accounting of stats in node and zone
o Kswapd will avoid more reclaim if an eligible zone is available
o Remove some duplications of sc->reclaim_idx and classzone_idx
o Print per-node stats in zoneinfo
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 4.7-rc4 with Andrew's tree applied. While this
is a current rebase, the test results were based on mmotm as of June 23rd.
Conceptually, this series 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-rc4 4.7.0-rc4
mmotm-20160623 nodelru-v8
Min total-odr0-1 490.00 ( 0.00%) 463.00 ( 5.51%)
Min total-odr0-2 349.00 ( 0.00%) 325.00 ( 6.88%)
Min total-odr0-4 288.00 ( 0.00%) 272.00 ( 5.56%)
Min total-odr0-8 250.00 ( 0.00%) 235.00 ( 6.00%)
Min total-odr0-16 234.00 ( 0.00%) 222.00 ( 5.13%)
Min total-odr0-32 223.00 ( 0.00%) 205.00 ( 8.07%)
Min total-odr0-64 217.00 ( 0.00%) 202.00 ( 6.91%)
Min total-odr0-128 214.00 ( 0.00%) 207.00 ( 3.27%)
Min total-odr0-256 242.00 ( 0.00%) 242.00 ( 0.00%)
Min total-odr0-512 272.00 ( 0.00%) 265.00 ( 2.57%)
Min total-odr0-1024 290.00 ( 0.00%) 283.00 ( 2.41%)
Min total-odr0-2048 302.00 ( 0.00%) 296.00 ( 1.99%)
Min total-odr0-4096 311.00 ( 0.00%) 306.00 ( 1.61%)
Min total-odr0-8192 314.00 ( 0.00%) 309.00 ( 1.59%)
Min total-odr0-16384 315.00 ( 0.00%) 309.00 ( 1.90%)
Min total-odr1-1 741.00 ( 0.00%) 716.00 ( 3.37%)
Min total-odr1-2 565.00 ( 0.00%) 524.00 ( 7.26%)
Min total-odr1-4 457.00 ( 0.00%) 427.00 ( 6.56%)
Min total-odr1-8 408.00 ( 0.00%) 371.00 ( 9.07%)
Min total-odr1-16 383.00 ( 0.00%) 344.00 ( 10.18%)
Min total-odr1-32 378.00 ( 0.00%) 334.00 ( 11.64%)
Min total-odr1-64 383.00 ( 0.00%) 334.00 ( 12.79%)
Min total-odr1-128 376.00 ( 0.00%) 342.00 ( 9.04%)
Min total-odr1-256 381.00 ( 0.00%) 343.00 ( 9.97%)
Min total-odr1-512 388.00 ( 0.00%) 349.00 ( 10.05%)
Min total-odr1-1024 386.00 ( 0.00%) 356.00 ( 7.77%)
Min total-odr1-2048 389.00 ( 0.00%) 362.00 ( 6.94%)
Min total-odr1-4096 389.00 ( 0.00%) 362.00 ( 6.94%)
Min total-odr1-8192 389.00 ( 0.00%) 362.00 ( 6.94%)
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-rc4 4.7.0-rc4
mmotm-20160623nodelru-v8
User 191.39 191.61
System 2651.24 2504.48
Elapsed 2904.40 2757.01
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-20160623 nodelru-v8
DMA32 allocs 28794771816 0
Normal allocs 48432582848 77227356392
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-rc4 4.7.0-rc4
mmotm-20160623 nodelru-v8
Min PotentialReadSpeed 89.65 ( 0.00%) 90.34 ( 0.77%)
Min SeqRead-MB/sec-1 82.68 ( 0.00%) 83.13 ( 0.54%)
Min SeqRead-MB/sec-2 72.76 ( 0.00%) 72.15 ( -0.84%)
Min SeqRead-MB/sec-4 75.13 ( 0.00%) 74.23 ( -1.20%)
Min SeqRead-MB/sec-8 64.91 ( 0.00%) 65.25 ( 0.52%)
Min SeqRead-MB/sec-16 62.24 ( 0.00%) 62.76 ( 0.84%)
Min RandRead-MB/sec-1 0.88 ( 0.00%) 0.95 ( 7.95%)
Min RandRead-MB/sec-2 0.95 ( 0.00%) 0.94 ( -1.05%)
Min RandRead-MB/sec-4 1.43 ( 0.00%) 1.46 ( 2.10%)
Min RandRead-MB/sec-8 1.61 ( 0.00%) 1.58 ( -1.86%)
Min RandRead-MB/sec-16 1.80 ( 0.00%) 1.93 ( 7.22%)
Min SeqWrite-MB/sec-1 76.41 ( 0.00%) 78.84 ( 3.18%)
Min SeqWrite-MB/sec-2 74.11 ( 0.00%) 73.35 ( -1.03%)
Min SeqWrite-MB/sec-4 80.05 ( 0.00%) 78.69 ( -1.70%)
Min SeqWrite-MB/sec-8 72.88 ( 0.00%) 71.38 ( -2.06%)
Min SeqWrite-MB/sec-16 75.91 ( 0.00%) 75.81 ( -0.13%)
Min RandWrite-MB/sec-1 1.18 ( 0.00%) 1.12 ( -5.08%)
Min RandWrite-MB/sec-2 1.02 ( 0.00%) 1.02 ( 0.00%)
Min RandWrite-MB/sec-4 1.05 ( 0.00%) 0.99 ( -5.71%)
Min RandWrite-MB/sec-8 0.89 ( 0.00%) 0.92 ( 3.37%)
Min RandWrite-MB/sec-16 0.92 ( 0.00%) 0.89 ( -3.26%)
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-rc4 4.7.0-rc4
mmotm-20160623nodelru-v8
Minor Faults 645838 644036
Major Faults 573 593
Swap Ins 0 0
Swap Outs 0 0
Allocation stalls 24 0
DMA allocs 0 0
DMA32 allocs 46041453 44154171
Normal allocs 78053072 79865782
Movable allocs 0 0
Direct pages scanned 10969 54504
Kswapd pages scanned 93375144 93250583
Kswapd pages reclaimed 93372243 93247714
Direct pages reclaimed 10969 54504
Kswapd efficiency 99% 99%
Kswapd velocity 13741.015 13711.950
Direct efficiency 100% 100%
Direct velocity 1.614 8.014
Percentage direct scans 0% 0%
Zone normal velocity 8641.875 13719.964
Zone dma32 velocity 5100.754 0.000
Zone dma velocity 0.000 0.000
Page writes by reclaim 0.000 0.000
Page writes file 0 0
Page writes anon 0 0
Page reclaim immediate 37 54
kswapd activity was roughly comparable. There were differences in direct
reclaim activity but negligible in the context of the overall workload
(velocity of 8 pages per second with the patches applied, 1.6 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-rc4 4.7.0-rc4
mmotm-20160623 nodelru-v8
Hmean 1 188.26 ( 0.00%) 189.78 ( 0.81%)
Hmean 5 330.66 ( 0.00%) 328.69 ( -0.59%)
Hmean 12 370.32 ( 0.00%) 380.72 ( 2.81%)
Hmean 21 368.89 ( 0.00%) 369.00 ( 0.03%)
Hmean 30 382.14 ( 0.00%) 360.89 ( -5.56%)
Hmean 32 428.87 ( 0.00%) 432.96 ( 0.95%)
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.
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-rc4 4.7.0-rc4
mmotm-20160623 nodelru-v8
Min mmap 16.6283 ( 0.00%) 16.1394 ( 2.94%)
1st-qrtle mmap 54.7570 ( 0.00%) 55.2975 ( -0.99%)
2nd-qrtle mmap 57.3163 ( 0.00%) 57.5230 ( -0.36%)
3rd-qrtle mmap 58.9976 ( 0.00%) 58.0537 ( 1.60%)
Max-90% mmap 59.7433 ( 0.00%) 58.3910 ( 2.26%)
Max-93% mmap 60.1298 ( 0.00%) 58.4801 ( 2.74%)
Max-95% mmap 73.4112 ( 0.00%) 58.5537 ( 20.24%)
Max-99% mmap 92.8542 ( 0.00%) 58.9673 ( 36.49%)
Max mmap 1440.6569 ( 0.00%) 137.6875 ( 90.44%)
Mean mmap 59.3493 ( 0.00%) 55.5153 ( 6.46%)
Best99%Mean mmap 57.2121 ( 0.00%) 55.4194 ( 3.13%)
Best95%Mean mmap 55.9113 ( 0.00%) 55.2813 ( 1.13%)
Best90%Mean mmap 55.6199 ( 0.00%) 55.1044 ( 0.93%)
Best50%Mean mmap 53.2183 ( 0.00%) 52.8330 ( 0.72%)
Best10%Mean mmap 45.9842 ( 0.00%) 42.3740 ( 7.85%)
Best5%Mean mmap 43.2256 ( 0.00%) 38.8660 ( 10.09%)
Best1%Mean mmap 32.9388 ( 0.00%) 27.7577 ( 15.73%)
This shows a number of improvements with the worst-case outlier greatly
improved.
Some of the vmstats are interesting
4.7.0-rc4 4.7.0-rc4
mmotm-20160623nodelru-v8
Swap Ins 163 239
Swap Outs 0 0
Allocation stalls 2603 0
DMA allocs 0 0
DMA32 allocs 618719206 1303037965
Normal allocs 891235743 229914091
Movable allocs 0 0
Direct pages scanned 216787 3173
Kswapd pages scanned 50719775 41732250
Kswapd pages reclaimed 41541765 41731168
Direct pages reclaimed 209159 3173
Kswapd efficiency 81% 99%
Kswapd velocity 16859.554 14231.043
Direct efficiency 96% 100%
Direct velocity 72.061 1.082
Percentage direct scans 0% 0%
Zone normal velocity 8431.777 14232.125
Zone dma32 velocity 8499.838 0.000
Zone dma velocity 0.000 0.000
Page writes by reclaim 6215049.000 0.000
Page writes file 6215049 0
Page writes anon 0 0
Page reclaim immediate 70673 143
Sector Reads 81940800 81489388
Sector Writes 100158984 99161860
Page rescued immediate 0 0
Slabs scanned 1366954 21196
While this is not guaranteed in all cases, this particular test showed
a large reduction in direct reclaim activity. It's also worth noting
that no page writes were issued 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 | 77 ++-
drivers/staging/android/lowmemorykiller.c | 12 +-
drivers/staging/lustre/lustre/osc/osc_cache.c | 6 +-
fs/fs-writeback.c | 4 +-
fs/fuse/file.c | 8 +-
fs/nfs/internal.h | 2 +-
fs/nfs/write.c | 2 +-
fs/proc/meminfo.c | 20 +-
include/linux/backing-dev.h | 2 +-
include/linux/memcontrol.h | 61 +-
include/linux/mm.h | 5 +
include/linux/mm_inline.h | 35 +-
include/linux/mm_types.h | 2 +-
include/linux/mmzone.h | 155 +++--
include/linux/swap.h | 24 +-
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 | 50 +-
mm/filemap.c | 16 +-
mm/huge_memory.c | 12 +-
mm/internal.h | 11 +-
mm/khugepaged.c | 14 +-
mm/memcontrol.c | 215 +++----
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 | 123 ++--
mm/page_alloc.c | 371 +++++------
mm/page_idle.c | 4 +-
mm/rmap.c | 26 +-
mm/shmem.c | 14 +-
mm/swap.c | 64 +-
mm/swap_state.c | 4 +-
mm/util.c | 4 +-
mm/vmscan.c | 879 +++++++++++++-------------
mm/vmstat.c | 398 +++++++++---
mm/workingset.c | 54 +-
50 files changed, 1674 insertions(+), 1319 deletions(-)
--
2.6.4
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