alloc profiler: adjust warnings in docs; remove logged warning from implementation (#44077)

* docs: update warning in the manual; add to reference

* remove missed allocs warning from `fetch`

since we think we've gotten all the allocs

* remove tests of warning message, since it's no longer there

Author: vilterp

doc/src/manual/profile.md

@@ -356,10 +356,12 @@ Passing `sample_rate=1.0` will make it record everything (which is slow);
 !!! note
 
     The current implementation of the Allocations Profiler _does not
-    capture all allocations._ You can read more about the missing allocations
-    and the plan to improve this, here: https://github.com/JuliaLang/julia/issues/43688.
-    Calling `Profile.Allocs.fetch()` will print a log line reporting the percentage
-    of missed allocations, so you can understand the accuracy of your profile.
+    capture types for all allocations._ Allocations for which the profiler
+    could not capture the type are represented as having type
+    `Profile.Allocs.UnknownType`.
+
+    You can read more about the missing types and the plan to improve this, here:
+    https://github.com/JuliaLang/julia/issues/43688.
 
 ## External Profiling
 

stdlib/Profile/src/Allocs.jl

@@ -44,6 +44,14 @@ julia> results = Profile.Allocs.fetch()
 julia> last(sort(results.allocs, by=x->x.size))
 Profile.Allocs.Alloc(Vector{Any}, Base.StackTraces.StackFrame[_new_array_ at array.c:127, ...], 5576)
 ```
+
+Note: The current implementation of the Allocations Profiler _does not
+capture types for all allocations._ Allocations for which the profiler
+could not capture the type are represented as having type
+`Profile.Allocs.UnknownType`.
+
+You can read more about the missing types and the plan to improve this, here:
+https://github.com/JuliaLang/julia/issues/43688.
 """
 macro profile(opts, ex)
     _prof_expr(ex, opts)
@@ -52,12 +60,6 @@ macro profile(ex)
     _prof_expr(ex, :(sample_rate=0.0001))
 end
 
-# globals used for tracking how many allocs we're missing
-# vs the alloc counters used by @time
-const _g_gc_num_before = Ref{Base.GC_Num}()
-const _g_sample_rate = Ref{Real}()
-const _g_expected_sampled_allocs = Ref{Float64}(0)
-
 function _prof_expr(expr, opts)
     quote
         $start(; $(esc(opts)))
@@ -77,9 +79,6 @@ A sample rate of 1.0 will record everything; 0.0 will record nothing.
 """
 function start(; sample_rate::Real)
     ccall(:jl_start_alloc_profile, Cvoid, (Cdouble,), Float64(sample_rate))
-
-    _g_sample_rate[] = sample_rate
-    _g_gc_num_before[] = Base.gc_num()
 end
 
 """
@@ -89,15 +88,6 @@ Stop recording allocations.
 """
 function stop()
     ccall(:jl_stop_alloc_profile, Cvoid, ())
-
-    # increment a counter of how many allocs we would expect
-    # the memory profiler to see, based on how many allocs
-    # actually happened.
-    gc_num_after = Base.gc_num()
-    gc_diff = Base.GC_Diff(gc_num_after, _g_gc_num_before[])
-    alloc_count = Base.gc_alloc_count(gc_diff)
-    expected_samples = alloc_count * _g_sample_rate[]
-    _g_expected_sampled_allocs[] += expected_samples
 end
 
 """
@@ -107,8 +97,6 @@ Clear all previously profiled allocation information from memory.
 """
 function clear()
     ccall(:jl_free_alloc_profile, Cvoid, ())
-
-    _g_expected_sampled_allocs[] = 0
     return nothing
 end
 
@@ -120,25 +108,7 @@ objects which can be analyzed.
 """
 function fetch()
     raw_results = ccall(:jl_fetch_alloc_profile, RawResults, ())
-    decoded_results = decode(raw_results)
-
-    # avoid divide-by-0 errors
-    if _g_expected_sampled_allocs[] > 0
-        missed_allocs = max(0, _g_expected_sampled_allocs[] - length(decoded_results.allocs))
-        missed_percentage = max(0, round(Int, missed_allocs / _g_expected_sampled_allocs[] * 100))
-        if missed_percentage > 0
-            @warn("The allocation profiler is not fully implemented, and missed approximately" *
-            " $(missed_percentage)% (estimated $(round(Int, missed_allocs)) / $(round(Int,
-            _g_expected_sampled_allocs[]))) " *
-                    "of sampled allocs in the last run. " *
-                    "For more info see https://github.com/JuliaLang/julia/issues/43688")
-        else
-            @warn("The allocation profiler is not fully implemented, and may have missed" *
-            " some of the allocs. " *
-                    "For more info see https://github.com/JuliaLang/julia/issues/43688")
-        end
-    end
-    return decoded_results
+    return decode(raw_results)
 end
 
 # decoded results

stdlib/Profile/test/allocs.jl

@@ -111,31 +111,6 @@ end
     Allocs.clear()
 end
 
-@testset "alloc profiler warning message" begin
-    @testset "no allocs" begin
-        Profile.Allocs.clear()
-        Profile.Allocs.fetch()
-    end
-    @testset "catches all allocations" begin
-        foo() = []
-        precompile(foo, ())
-        Profile.Allocs.clear()
-        Profile.Allocs.@profile sample_rate=1 foo()
-        # Fake that we expected exactly 1 alloc, since we should have recorded >= 1
-        Profile.Allocs._g_expected_sampled_allocs[] = 1
-        @assert length(Profile.Allocs.fetch().allocs) >= 1
-    end
-    @testset "misses some allocations" begin
-        foo() = []
-        precompile(foo, ())
-        Profile.Allocs.clear()
-        Profile.Allocs.@profile sample_rate=1 foo()
-        # Fake some allocs that we missed, to force the print statement
-        Profile.Allocs._g_expected_sampled_allocs[] += 10
-        @assert 1 <= length(Profile.Allocs.fetch().allocs) < 10
-    end
-end
-
 @testset "alloc profiler catches strings" begin
     Allocs.@profile sample_rate=1 "$(rand())"