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runtime: improve heap hugepage utilization #59960

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mknyszek opened this issue May 3, 2023 · 5 comments
Closed

runtime: improve heap hugepage utilization #59960

mknyszek opened this issue May 3, 2023 · 5 comments
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compiler/runtime Issues related to the Go compiler and/or runtime. NeedsFix The path to resolution is known, but the work has not been done.
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Go1.21

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mknyszek commented May 3, 2023 •
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Background

Transparent huge pages (THP) admin guide.
Go scavenging policy. (Implementation details are out-of-date, but linked policy is relevant.)

Motivation

Currently, Go's hugepage-related policies do not play well together and have bit-rotted. The result is that the memory regions the Go runtime chooses to mark as MADV_NOHUGEPAGE and MADV_HUGEPAGE are somewhat haphazard, resulting in memory overuse for small heaps. The memory overuse is upwards of 40% memory overhead in some cases. Turning off huge pages entirely fixes the problem, but leaves CPU performance on the table. This policy also means large heaps might have dense sections that are erroneously mapped as MADV_NOHUGEPAGE, costing up to 1% throughput.

The goal of this work is to eliminate this overhead for small heaps while improving huge page utilization for large heaps.

Design

Full design doc soon. (CL)

TL;DR: Determine which parts of the heap should be backed by huge pages based on near-future density of page allocator chunks. This density heuristic is then also used to delay the background scavenger: only chunks that have been sparse for at least one GC cycle are eligible for scavenging. The scavenger also breaks up hugepages.
@mknyszek mknyszek added the NeedsFix The path to resolution is known, but the work has not been done. label May 3, 2023
@mknyszek mknyszek added this to the Go1.21 milestone May 3, 2023
@mknyszek mknyszek self-assigned this May 3, 2023
@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label May 3, 2023
@mknyszek mknyszek closed this as completed May 3, 2023
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mknyszek commented May 3, 2023

Landed in https://go.dev/cl/436395.

@mknyszek mknyszek changed the title runtime: hugepage-aware heap runtime: improve heap hugepage utilization May 3, 2023
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Change https://go.dev/cl/492018 mentions this issue: design/59960-heap-hugepage-util.md: add design

gopherbot pushed a commit to golang/proposal that referenced this issue Jun 13, 2023
@mknyszek
design/59960-heap-hugepage-util.md: add design
60fce05 
For golang/go#59960.

Change-Id: I4c6ee87db54952ccacdfa6c66b419356e5842620
Reviewed-on: https://go-review.googlesource.com/c/proposal/+/492018
Reviewed-by: Michael Pratt <mpratt@google.com>
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Change https://go.dev/cl/531816 mentions this issue: runtime: don't eagerly collapse hugepages

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Change https://go.dev/cl/532117 mentions this issue: runtime: delete hugepage tracking dead code

gopherbot pushed a commit that referenced this issue Oct 2, 2023
@mknyszek @gopherbot
runtime: don't eagerly collapse hugepages
595deec 
This has caused performance issues in production environments.

Disable it until further notice.

Fixes #63334.
Related to #61718 and #59960.

Change-Id: If84c5a8685825d43c912a71418f2597e44e867e5
Reviewed-on: https://go-review.googlesource.com/c/go/+/531816
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
gopherbot pushed a commit that referenced this issue Oct 2, 2023
@mknyszek @gopherbot
runtime: delete hugepage tracking dead code
765dfb0 
After the previous CL, this is now all dead code. This change is
separated out to make the previous one easy to backport.

For #63334.
Related to #61718 and #59960.

Change-Id: I109673ed97c62c472bbe2717dfeeb5aa4fc883ea
Reviewed-on: https://go-review.googlesource.com/c/go/+/532117
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
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Change https://go.dev/cl/532255 mentions this issue: [release-branch.go1.21] runtime: don't eagerly collapse hugepages

gopherbot pushed a commit that referenced this issue Oct 12, 2023
@mknyszek @gopherbot
[release-branch.go1.21] runtime: don't eagerly collapse hugepages
ef6993f 
This has caused performance issues in production environments.

MADV_COLLAPSE can go into direct reclaim, but we call it with the heap
lock held. This means that the process could end up stalled fairly
quickly if just one allocating goroutine ends up in the madvise call, at
least until the madvise(MADV_COLLAPSE) call returns. A similar issue
occurred with madvise(MADV_HUGEPAGE), because that could go into direct
reclaim on any page fault for MADV_HUGEPAGE-marked memory.

My understanding was that the calls to madvise(MADV_COLLAPSE) were
fairly rare, and it's "best-effort" nature prevented it from going into
direct reclaim often, but this was wrong. It tends to be fairly
heavyweight even when it doesn't end up in direct reclaim, and it's
almost certainly not worth it.

Disable it until further notice and let the kernel fully dictate
hugepage policy. The updated scavenger policy is still more hugepage
friendly by delaying scavening until hugepages are no longer densely
packed, so we don't lose all that much.

The Sweet benchmarks show a minimal difference. A couple less realistic
benchmarks seem to slow down a bit; they might just be getting unlucky
with what the kernel decides to back with a huge page. Some benchmarks
on the other hand improve. Overall, it's a wash.

name                  old time/op            new time/op            delta
BiogoIgor                        13.1s ± 1%             13.2s ± 2%    ~     (p=0.182 n=9+10)
BiogoKrishna                     12.0s ± 1%             12.1s ± 1%  +1.23%  (p=0.002 n=9+10)
BleveIndexBatch100               4.51s ± 4%             4.56s ± 3%    ~     (p=0.393 n=10+10)
EtcdPut                         20.2ms ± 4%            19.8ms ± 2%    ~     (p=0.079 n=10+9)
EtcdSTM                          109ms ± 3%             111ms ± 3%  +1.63%  (p=0.035 n=10+10)
GoBuildKubelet                   31.2s ± 1%             31.3s ± 1%    ~     (p=0.780 n=9+10)
GoBuildKubeletLink               7.77s ± 0%             7.81s ± 2%    ~     (p=0.237 n=8+10)
GoBuildIstioctl                  31.8s ± 1%             31.7s ± 0%    ~     (p=0.136 n=9+9)
GoBuildIstioctlLink              7.88s ± 1%             7.89s ± 1%    ~     (p=0.720 n=9+10)
GoBuildFrontend                  11.7s ± 1%             11.8s ± 1%    ~     (p=0.278 n=10+9)
GoBuildFrontendLink              1.15s ± 4%             1.15s ± 5%    ~     (p=0.387 n=9+9)
GopherLuaKNucleotide             19.7s ± 1%             20.6s ± 0%  +4.48%  (p=0.000 n=10+10)
MarkdownRenderXHTML              194ms ± 3%             196ms ± 3%    ~     (p=0.356 n=9+10)
Tile38QueryLoad                  633µs ± 2%             629µs ± 2%    ~     (p=0.075 n=10+10)

name                  old average-RSS-bytes  new average-RSS-bytes  delta
BiogoIgor                       69.2MB ± 3%            68.4MB ± 1%    ~     (p=0.190 n=10+10)
BiogoKrishna                    4.40GB ± 0%            4.40GB ± 0%    ~     (p=0.605 n=9+9)
BleveIndexBatch100               195MB ± 3%             195MB ± 2%    ~     (p=0.853 n=10+10)
EtcdPut                          107MB ± 4%             108MB ± 3%    ~     (p=0.190 n=10+10)
EtcdSTM                         91.6MB ± 5%            92.6MB ± 4%    ~     (p=0.481 n=10+10)
GoBuildKubelet                  2.26GB ± 1%            2.28GB ± 1%  +1.22%  (p=0.000 n=10+10)
GoBuildIstioctl                 1.53GB ± 0%            1.53GB ± 0%  +0.21%  (p=0.017 n=9+10)
GoBuildFrontend                  556MB ± 1%             554MB ± 2%    ~     (p=0.497 n=9+10)
GopherLuaKNucleotide            39.0MB ± 3%            39.0MB ± 1%    ~     (p=1.000 n=10+8)
MarkdownRenderXHTML             21.2MB ± 2%            21.4MB ± 3%    ~     (p=0.190 n=10+10)
Tile38QueryLoad                 5.99GB ± 2%            6.02GB ± 0%    ~     (p=0.243 n=10+9)

name                  old peak-RSS-bytes     new peak-RSS-bytes     delta
BiogoIgor                       90.2MB ± 4%            89.2MB ± 2%    ~     (p=0.143 n=10+10)
BiogoKrishna                    4.49GB ± 0%            4.49GB ± 0%    ~     (p=0.190 n=10+10)
BleveIndexBatch100               283MB ± 8%             274MB ± 6%    ~     (p=0.075 n=10+10)
EtcdPut                          147MB ± 4%             149MB ± 2%  +1.55%  (p=0.034 n=10+8)
EtcdSTM                          117MB ± 5%             117MB ± 4%    ~     (p=0.905 n=9+10)
GopherLuaKNucleotide            44.9MB ± 1%            44.6MB ± 1%    ~     (p=0.083 n=8+8)
MarkdownRenderXHTML             22.0MB ± 8%            22.1MB ± 9%    ~     (p=0.436 n=10+10)
Tile38QueryLoad                 6.24GB ± 2%            6.29GB ± 2%    ~     (p=0.218 n=10+10)

name                  old peak-VM-bytes      new peak-VM-bytes      delta
BiogoIgor                       1.33GB ± 0%            1.33GB ± 0%    ~     (p=0.504 n=10+9)
BiogoKrishna                    5.77GB ± 0%            5.77GB ± 0%    ~     (p=1.000 n=10+9)
BleveIndexBatch100              3.53GB ± 0%            3.53GB ± 0%    ~     (p=0.642 n=10+10)
EtcdPut                         12.1GB ± 0%            12.1GB ± 0%    ~     (p=0.564 n=10+10)
EtcdSTM                         12.1GB ± 0%            12.1GB ± 0%    ~     (p=0.633 n=10+10)
GopherLuaKNucleotide            1.26GB ± 0%            1.26GB ± 0%    ~     (p=0.297 n=9+10)
MarkdownRenderXHTML             1.26GB ± 0%            1.26GB ± 0%    ~     (p=0.069 n=10+10)
Tile38QueryLoad                 7.47GB ± 2%            7.53GB ± 2%    ~     (p=0.280 n=10+10)

name                  old p50-latency-ns     new p50-latency-ns     delta
EtcdPut                          19.8M ± 5%             19.3M ± 3%  -2.74%  (p=0.043 n=10+9)
EtcdSTM                          81.4M ± 4%             83.4M ± 4%  +2.46%  (p=0.029 n=10+10)
Tile38QueryLoad                   241k ± 1%              240k ± 1%    ~     (p=0.393 n=10+10)

name                  old p90-latency-ns     new p90-latency-ns     delta
EtcdPut                          30.4M ± 5%             30.6M ± 5%    ~     (p=0.971 n=10+10)
EtcdSTM                           222M ± 3%              226M ± 4%    ~     (p=0.063 n=10+10)
Tile38QueryLoad                   687k ± 2%              691k ± 1%    ~     (p=0.173 n=10+8)

name                  old p99-latency-ns     new p99-latency-ns     delta
EtcdPut                          42.3M ±10%             41.4M ± 7%    ~     (p=0.353 n=10+10)
EtcdSTM                           486M ± 7%              487M ± 4%    ~     (p=0.579 n=10+10)
Tile38QueryLoad                  6.43M ± 2%             6.37M ± 3%    ~     (p=0.280 n=10+10)

name                  old ops/s              new ops/s              delta
EtcdPut                          48.6k ± 3%             49.5k ± 2%    ~     (p=0.065 n=10+9)
EtcdSTM                          9.09k ± 2%             8.95k ± 3%  -1.56%  (p=0.045 n=10+10)
Tile38QueryLoad                  28.4k ± 1%             28.6k ± 1%  +0.87%  (p=0.016 n=9+10)

Fixes #63335.
For #63334.
Related to #61718 and #59960.

Change-Id: If84c5a8685825d43c912a71418f2597e44e867e5
Reviewed-on: https://go-review.googlesource.com/c/go/+/531816
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
(cherry picked from commit 595deec)
Reviewed-on: https://go-review.googlesource.com/c/go/+/532255
Auto-Submit: Dmitri Shuralyov <dmitshur@google.com>
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