Instrument GC with memory profiler implementation

This adds C support for a memory profiler within the GC, tracking
locations of allocations, deallocations, etc...  It operates in a
similar manner as the time profiler with single large buffers setup
beforehand through an initialization function, reducing the need for
expensive allocations while the program being measured is running.

The memory profiler instruments the GC in all locations that the GC
statistics themselves are being modified (e.g. `gc_num.allocd` and
`gc_num.freed`) by introducing new helper functions
`jl_gc_count_{allocd,freed,reallocd}()`.  Those utility functions call
the `jl_memprofile_track_{de,}alloc()` method to register an address,
a size and a tag with the memory profiler.  We also track type
information as this can be critically helpful when debugging, and to do
so without breaking API guarantees we insert methods to set the type of
a chunk of memory after allocating it where necessary.

The tagging system allows the memory profiler to disambiguate, at
profile time, between e.g. pooled allocations and the "big" allocator.
It also allows the memory allocator to support tracking multiple "memory
domains", e.g. a GPU support package could manually call
`jl_memprofile_track_alloc()` any time a chunk of memory is allocated on
the GPU so as to use the same system.  By default, all values are
tracked, however one can set a `memprof_tag_filter` value to track only
the values you are most interested in.  (E.g. only CPU domain big
allocations)

base/error.jl

@@ -65,8 +65,16 @@ struct InterpreterIP
     mod::Union{Module,Nothing}
 end
 
-# formatted backtrace buffers can contain all types of objects (none for now though)
-const BackTraceEntry = Union{Ptr{Nothing}, InterpreterIP}
+struct AllocationInfo
+    T::Union{Nothing,Type}
+    address::Ptr{Cvoid}
+    time::Float64
+    allocsz::Csize_t
+    tag::UInt16
+end
+
+# formatted backtrace buffers can contain all types of objects
+const BackTraceEntry = Union{Ptr{Nothing}, InterpreterIP, AllocationInfo}
 # but only some correspond with actual instruction pointers
 const InstructionPointer = Union{Ptr{Nothing}, InterpreterIP}
 
@@ -114,6 +122,18 @@ function _reformat_bt(bt, Wanted::Type=BackTraceEntry)
                 end
                 push!(ret, InterpreterIP(code, header, mod))
             end
+        elseif tag == 2 # JL_BT_ALLOCINFO_FRAME_TAG
+            if AllocationInfo <: Wanted
+                #@assert header == 0
+                #@assert njlvalues == 1
+                type = unsafe_pointer_to_objref(convert(Ptr{Any}, bt[i+2]))
+                #@assert nuintvals == 4
+                address = reinterpret(Ptr{Cvoid}, bt[i+3])
+                time = reinterpret(Cdouble, bt[i+4])
+                allocsz = reinterpret(UInt, bt[i+5])
+                tag = reinterpret(UInt, bt[i+6])
+                push!(ret, AllocationInfo(type, address, time, allocsz, tag))
+            end
         else
             # Tags we don't know about are an error
             throw(ArgumentError("Unexpected extended backtrace entry tag $tag at bt[$i]"))

src/array.c

@@ -98,6 +98,7 @@ static jl_array_t *_new_array_(jl_value_t *atype, uint32_t ndims, size_t *dims,
         tsz += tot;
         tsz = JL_ARRAY_ALIGN(tsz, JL_SMALL_BYTE_ALIGNMENT); // align whole object
         a = (jl_array_t*)jl_gc_alloc(ptls, tsz, atype);
+        jl_memprofile_set_typeof(a, atype);
         // No allocation or safepoint allowed after this
         a->flags.how = 0;
         data = (char*)a + doffs;
@@ -107,12 +108,14 @@ static jl_array_t *_new_array_(jl_value_t *atype, uint32_t ndims, size_t *dims,
     else {
         tsz = JL_ARRAY_ALIGN(tsz, JL_CACHE_BYTE_ALIGNMENT); // align whole object
         data = jl_gc_managed_malloc(tot);
+        jl_memprofile_set_typeof(data, atype);
         // Allocate the Array **after** allocating the data
         // to make sure the array is still young
         a = (jl_array_t*)jl_gc_alloc(ptls, tsz, atype);
         // No allocation or safepoint allowed after this
         a->flags.how = 2;
         jl_gc_track_malloced_array(ptls, a);
+        jl_memprofile_set_typeof(a, atype);
         if (!isunboxed || isunion)
             // need to zero out isbits union array selector bytes to ensure a valid type index
             memset(data, 0, tot);
@@ -334,7 +337,9 @@ JL_DLLEXPORT jl_array_t *jl_ptr_to_array_1d(jl_value_t *atype, void *data,
     if (own_buffer) {
         a->flags.how = 2;
         jl_gc_track_malloced_array(ptls, a);
-        jl_gc_count_allocd(nel*elsz + (elsz == 1 ? 1 : 0));
+        jl_gc_count_allocd(a, nel*elsz + (elsz == 1 ? 1 : 0),
+                           JL_MEMPROF_TAG_DOMAIN_CPU | JL_MEMPROF_TAG_ALLOC_STDALLOC);
+        jl_memprofile_set_typeof(a, atype);
     }
     else {
         a->flags.how = 0;
@@ -401,7 +406,9 @@ JL_DLLEXPORT jl_array_t *jl_ptr_to_array(jl_value_t *atype, void *data,
     if (own_buffer) {
         a->flags.how = 2;
         jl_gc_track_malloced_array(ptls, a);
-        jl_gc_count_allocd(nel*elsz + (elsz == 1 ? 1 : 0));
+        jl_gc_count_allocd(a, nel*elsz + (elsz == 1 ? 1 : 0),
+                           JL_MEMPROF_TAG_DOMAIN_CPU | JL_MEMPROF_TAG_ALLOC_STDALLOC);
+        jl_memprofile_set_typeof(a, atype);
     }
     else {
         a->flags.how = 0;
@@ -669,6 +676,7 @@ static int NOINLINE array_resize_buffer(jl_array_t *a, size_t newlen)
             a->flags.how = 1;
             jl_gc_wb_buf(a, a->data, nbytes);
         }
+        jl_memprofile_set_typeof(a->data, jl_typeof(a));
     }
     if (JL_ARRAY_IMPL_NUL && elsz == 1 && !isbitsunion)
         memset((char*)a->data + oldnbytes - 1, 0, nbytes - oldnbytes + 1);