trace: update tracing-subscriber to 0.2.0-alpha.6 (#423)

Version 0.0.7 of `sharded-slab` contains a bug where, when the `remove`
method is called with the index of a slot that is not being accessed
concurrently, the slot is emptied but **not** placed on the free list.
This issue meant that, under `tracing-subscriber`'s usage pattern, where
slab entries are almost always uncontended when reused, allocated slab
pages are almost never reused, resulting in unbounded slab growth over
time (i.e. a memory leak).

This commit updates `tracing-subscriber`' to version 0.2.0-alpha.6,
which in turn bumps the `sharded-slab` dependency to v0.0.8, which
includes commit hawkw/sharded-slab@dfdd7ae. That commit fixes this bug.

I've empirically verified that, after running `linkerd2-proxy` under
load with a global `trace` filter that enables a *lot* of spans, heap
usage remains stable, and the characteristic stair-step heap growth
pattern of doubling slab allocations doesn't occur. This indicates that
freed slots are actually being reused, and (once fully warmed up), the
slab will only grow when the number of active spans in the system
increases.

![mem_plot](https://user-images.githubusercontent.com/2796466/73581369-cd859900-443d-11ea-8522-abeace03d745.png)

Closes linkerd/linkerd2#3998 

Signed-off-by: Eliza Weisman <[email protected]>

Author: hawkw

Cargo.lock

@@ -138,11 +138,10 @@ checksum = "b486ce3ccf7ffd79fdeb678eac06a9e6c09fc88d33836340becb8fffe87c5e33"
 
 [[package]]
 name = "chrono"
-version = "0.4.9"
+version = "0.4.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e8493056968583b0193c1bb04d6f7684586f3726992d6c573261941a895dbd68"
+checksum = "31850b4a4d6bae316f7a09e691c944c28299298837edc0a03f755618c23cbc01"
 dependencies = [
- "libc",
  "num-integer",
  "num-traits 0.2.6",
  "time",
@@ -1900,9 +1899,9 @@ dependencies = [
 
 [[package]]
 name = "sharded-slab"
-version = "0.0.7"
+version = "0.0.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "73ee8b66dea1777ef2c5f33ffeb90fd54afe43bb5c97bdaf82b521ad7c90a395"
+checksum = "ae75d0445b5d3778c9da3d1f840faa16d0627c8607f78a74daf69e5b988c39a1"
 dependencies = [
  "lazy_static",
 ]
@@ -1919,6 +1918,12 @@ version = "0.6.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ab606a9c5e214920bb66c458cd7be8ef094f813f20fe77a54cc7dbfff220d4b7"
 
+[[package]]
+name = "smallvec"
+version = "1.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5c2fb2ec9bcd216a5b0d0ccf31ab17b5ed1d627960edff65bbe95d3ce221cefc"
+
 [[package]]
 name = "socket2"
 version = "0.3.5"
@@ -2560,9 +2565,9 @@ dependencies = [
 
 [[package]]
 name = "tracing-subscriber"
-version = "0.2.0-alpha.4"
+version = "0.2.0-alpha.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "51ec8cdf2ebadeefbb5a0fac5f3d54757415cdcc46f40542eaa0be56cd6d6361"
+checksum = "8178ab65c2ae72cd431fcdb51e7317fb0b48d64599e66d52c7b64cd86ee5b482"
 dependencies = [
  "ansi_term",
  "chrono",
@@ -2572,7 +2577,7 @@ dependencies = [
  "serde",
  "serde_json",
  "sharded-slab",
- "smallvec",
+ "smallvec 1.2.0",
  "tracing-core",
  "tracing-log",
  "tracing-serde",
@@ -2590,7 +2595,7 @@ dependencies = [
  "lazy_static",
  "log",
  "rand 0.6.5",
- "smallvec",
+ "smallvec 0.6.10",
  "socket2",
  "tokio-executor",
  "tokio-io",
@@ -2614,7 +2619,7 @@ dependencies = [
  "log",
  "lru-cache",
  "resolv-conf",
- "smallvec",
+ "smallvec 0.6.10",
  "tokio",
  "trust-dns-proto",
 ]

linkerd/app/core/Cargo.toml

@@ -63,10 +63,10 @@ tracing-futures = "0.1"
 tracing-log = "0.1"
 
 [dependencies.tracing-subscriber]
-version = "0.2.0-alpha.4"
-# we don't need ANSI colors or `chrono` time formatting
+version = "0.2.0-alpha.6"
+# we don't need `chrono` time formatting
 default-features = false
-features = ["env-filter", "fmt", "smallvec", "tracing-log"]
+features = ["env-filter", "fmt", "smallvec", "tracing-log", "ansi"]
 
 [target.'cfg(target_os = "linux")'.dependencies]
 libc = "0.2"

linkerd/app/core/src/trace.rs

@@ -41,7 +41,8 @@ pub fn with_filter(filter: impl AsRef<str>) -> (Dispatch, LevelHandle) {
     let builder = FmtSubscriber::builder()
         .with_timer(Uptime { start_time })
         .with_env_filter(filter)
-        .with_filter_reloading();
+        .with_filter_reloading()
+        .with_ansi(cfg!(test));
     let handle = LevelHandle {
         inner: builder.reload_handle(),
     };

linkerd/proxy/transport/Cargo.toml

@@ -36,4 +36,4 @@ libc = "0.2"
 [dev-dependencies]
 linkerd2-identity = { path = "../../identity", features = ["test-util"] }
 tower-util = "0.1"
-tracing-subscriber = "0.2.0-alpha.4"
+tracing-subscriber = "0.2.0-alpha.6"