Allocation Profiler: Types for all allocations (JuliaLang#50337) (#34)

Backports PR JuliaLang#50337 for RAI julia v1.9.2

Original description:

===================

Pass the types to the allocator functions.

-------

Before this PR, we were missing the types for allocations in two cases:

1. allocations from codegen
2. allocations in `gc_managed_realloc_`

The second one is easy: those are always used for buffers, right?

For the first one: we extend the allocation functions called from
codegen, to take the type as a parameter, and set the tag there.

I kept the old interfaces around, since I think that they cannot be
removed due to supporting legacy code?

------

An example of the generated code:
```julia
  %ptls_field6 = getelementptr inbounds {}**, {}*** %4, i64 2
  %13 = bitcast {}*** %ptls_field6 to i8**
  %ptls_load78 = load i8*, i8** %13, align 8
  %box = call noalias nonnull dereferenceable(32) {}* @ijl_gc_pool_alloc_typed(i8* %ptls_load78, i32 1184, i32 32, i64 4366152144) #7
```

Fixes JuliaLang#43688.
Fixes JuliaLang#45268.

Co-authored-by: Valentin Churavy <[email protected]>

Author: 2 people

doc/src/manual/profile.md

@@ -310,7 +310,122 @@ the amount of memory allocated by each line of code.
 
 ### Line-by-Line Allocation Tracking
 
-To measure allocation line-by-line, start Julia with the `--track-allocation=<setting>` command-line
+While [`@time`](@ref) logs high-level stats about memory usage and garbage collection over the course
+of evaluating an expression, it can be useful to log each garbage collection event, to get an
+intuitive sense of how often the garbage collector is running, how long it's running each time,
+and how much garbage it collects each time. This can be enabled with
+[`GC.enable_logging(true)`](@ref), which causes Julia to log to stderr every time
+a garbage collection happens.
+
+### [Allocation Profiler](@id allocation-profiler)
+
+!!! compat "Julia 1.8"
+    This functionality requires at least Julia 1.8.
+
+The allocation profiler records the stack trace, type, and size of each
+allocation while it is running. It can be invoked with
+[`Profile.Allocs.@profile`](@ref).
+
+This information about the allocations is returned as an array of `Alloc`
+objects, wrapped in an `AllocResults` object. The best way to visualize these is
+currently with the [PProf.jl](https://github.com/JuliaPerf/PProf.jl) and
+[ProfileCanvas.jl](https://github.com/pfitzseb/ProfileCanvas.jl) packages, which
+can visualize the call stacks which are making the most allocations.
+
+The allocation profiler does have significant overhead, so a `sample_rate`
+argument can be passed to speed it up by making it skip some allocations.
+Passing `sample_rate=1.0` will make it record everything (which is slow);
+`sample_rate=0.1` will record only 10% of the allocations (faster), etc.
+
+!!! compat "Julia 1.11"
+
+    Older versions of Julia could not capture types in all cases. In older versions of
+    Julia, if you see an allocation of type `Profile.Allocs.UnknownType`, it means that
+    the profiler doesn't know what type of object was allocated. This mainly happened when
+    the allocation was coming from generated code produced by the compiler. See
+    [issue #43688](https://github.com/JuliaLang/julia/issues/43688) for more info.
+
+    Since Julia 1.11, all allocations should have a type reported.
+
+For more details on how to use this tool, please see the following talk from JuliaCon 2022:
+https://www.youtube.com/watch?v=BFvpwC8hEWQ
+
+##### Allocation Profiler Example
+
+In this simple example, we use PProf to visualize the alloc profile. You could use another
+visualization tool instead. We collect the profile (specifying a sample rate), then we visualize it.
+```julia
+using Profile, PProf
+Profile.Allocs.clear()
+Profile.Allocs.@profile sample_rate=0.0001 my_function()
+PProf.Allocs.pprof()
+```
+
+Here is a more in-depth example, showing how we can tune the sample rate. A
+good number of samples to aim for is around 1 - 10 thousand. Too many, and the
+profile visualizer can get overwhelmed, and profiling will be slow. Too few,
+and you don't have a representative sample.
+
+
+```julia-repl
+julia> import Profile
+
+julia> @time my_function()  # Estimate allocations from a (second-run) of the function
+  0.110018 seconds (1.50 M allocations: 58.725 MiB, 17.17% gc time)
+500000
+
+julia> Profile.Allocs.clear()
+
+julia> Profile.Allocs.@profile sample_rate=0.001 begin   # 1.5 M * 0.001 = ~1.5K allocs.
+           my_function()
+       end
+500000
+
+julia> prof = Profile.Allocs.fetch();  # If you want, you can also manually inspect the results.
+
+julia> length(prof.allocs)  # Confirm we have expected number of allocations.
+1515
+
+julia> using PProf  # Now, visualize with an external tool, like PProf or ProfileCanvas.
+
+julia> PProf.Allocs.pprof(prof; from_c=false)  # You can optionally pass in a previously fetched profile result.
+Analyzing 1515 allocation samples... 100%|████████████████████████████████| Time: 0:00:00
+Main binary filename not available.
+Serving web UI on http://localhost:62261
+"alloc-profile.pb.gz"
+```
+Then you can view the profile by navigating to http://localhost:62261, and the profile is saved to disk.
+See PProf package for more options.
+
+##### Allocation Profiling Tips
+
+As stated above, aim for around 1-10 thousand samples in your profile.
+
+Note that we are uniformly sampling in the space of _all allocations_, and are not weighting
+our samples by the size of the allocation. So a given allocation profile may not give a
+representative profile of where most bytes are allocated in your program, unless you had set
+`sample_rate=1`.
+
+Allocations can come from users directly constructing objects, but can also come from inside
+the runtime or be inserted into compiled code to handle type instability. Looking at the
+"source code" view can be helpful to isolate them, and then other external tools such as
+[`Cthulhu.jl`](https://github.com/JuliaDebug/Cthulhu.jl) can be useful for identifying the
+cause of the allocation.
+
+##### Allocation Profile Visualization Tools
+
+There are several profiling visualization tools now that can all display Allocation
+Profiles. Here is a small list of some of the main ones we know about:
+- [PProf.jl](https://github.com/JuliaPerf/PProf.jl)
+- [ProfileCanvas.jl](https://github.com/pfitzseb/ProfileCanvas.jl)
+- VSCode's built-in profile visualizer (`@profview_allocs`) [docs needed]
+- Viewing the results directly in the REPL
+  - You can inspect the results in the REPL via [`Profile.Allocs.fetch()`](@ref), to view
+    the stacktrace and type of each allocation.
+
+#### Line-by-Line Allocation Tracking
+
+An alternative way to measure allocations is to start Julia with the `--track-allocation=<setting>` command-line
 option, for which you can choose `none` (the default, do not measure allocation), `user` (measure
 memory allocation everywhere except Julia's core code), or `all` (measure memory allocation at
 each line of Julia code). Allocation gets measured for each line of compiled code. When you quit

src/gc-alloc-profiler.h

@@ -35,6 +35,7 @@ void _maybe_record_alloc_to_profile(jl_value_t *val, size_t size, jl_datatype_t
 
 extern int g_alloc_profile_enabled;
 
+// This should only be used from _deprecated_ code paths. We shouldn't see UNKNOWN anymore.
 #define jl_gc_unknown_type_tag ((jl_datatype_t*)0xdeadaa03)
 
 static inline void maybe_record_alloc_to_profile(jl_value_t *val, size_t size, jl_datatype_t *typ) JL_NOTSAFEPOINT {

src/gc.c

@@ -1177,14 +1177,21 @@ static inline jl_value_t *jl_gc_big_alloc_inner(jl_ptls_t ptls, size_t sz)
     return jl_valueof(&v->header);
 }
 
-// Instrumented version of jl_gc_big_alloc_inner, called into by LLVM-generated code.
+// Deprecated version, supported for legacy code.
 JL_DLLEXPORT jl_value_t *jl_gc_big_alloc(jl_ptls_t ptls, size_t sz)
 {
     jl_value_t *val = jl_gc_big_alloc_inner(ptls, sz);
 
     maybe_record_alloc_to_profile(val, sz, jl_gc_unknown_type_tag);
     return val;
 }
+// Instrumented version of jl_gc_big_alloc_inner, called into by LLVM-generated code.
+JL_DLLEXPORT jl_value_t *jl_gc_big_alloc_instrumented(jl_ptls_t ptls, size_t sz, jl_value_t *type)
+{
+    jl_value_t *val = jl_gc_big_alloc_inner(ptls, sz);
+    maybe_record_alloc_to_profile(val, sz, (jl_datatype_t*)type);
+    return val;
+}
 
 // This wrapper exists only to prevent `jl_gc_big_alloc_inner` from being inlined into
 // its callers. We provide an external-facing interface for callers, and inline `jl_gc_big_alloc_inner`
@@ -1494,7 +1501,7 @@ static inline jl_value_t *jl_gc_pool_alloc_inner(jl_ptls_t ptls, int pool_offset
     return jl_valueof(v);
 }
 
-// Instrumented version of jl_gc_pool_alloc_inner, called into by LLVM-generated code.
+// Deprecated version, supported for legacy code.
 JL_DLLEXPORT jl_value_t *jl_gc_pool_alloc(jl_ptls_t ptls, int pool_offset,
                                           int osize)
 {
@@ -1503,6 +1510,14 @@ JL_DLLEXPORT jl_value_t *jl_gc_pool_alloc(jl_ptls_t ptls, int pool_offset,
     maybe_record_alloc_to_profile(val, osize, jl_gc_unknown_type_tag);
     return val;
 }
+// Instrumented version of jl_gc_pool_alloc_inner, called into by LLVM-generated code.
+JL_DLLEXPORT jl_value_t *jl_gc_pool_alloc_instrumented(jl_ptls_t ptls, int pool_offset,
+                                        int osize, jl_value_t* type)
+{
+    jl_value_t *val = jl_gc_pool_alloc_inner(ptls, pool_offset, osize);
+    maybe_record_alloc_to_profile(val, osize, (jl_datatype_t*)type);
+    return val;
+}
 
 // This wrapper exists only to prevent `jl_gc_pool_alloc_inner` from being inlined into
 // its callers. We provide an external-facing interface for callers, and inline `jl_gc_pool_alloc_inner`
@@ -4054,7 +4069,10 @@ static void *gc_managed_realloc_(jl_ptls_t ptls, void *d, size_t sz, size_t olds
     SetLastError(last_error);
 #endif
     errno = last_errno;
-    maybe_record_alloc_to_profile((jl_value_t*)b, sz, jl_gc_unknown_type_tag);
+    // gc_managed_realloc_ is currently used exclusively for resizing array buffers.
+    if (allocsz > oldsz) {
+        maybe_record_alloc_to_profile((jl_value_t*)b, allocsz - oldsz, (jl_datatype_t*)jl_buff_tag);
+    }
     return b;
 }
 

src/jl_exported_funcs.inc

@@ -160,6 +160,7 @@
     XX(jl_gc_alloc_3w) \
     XX(jl_gc_alloc_typed) \
     XX(jl_gc_big_alloc) \
+    XX(jl_gc_big_alloc_instrumented) \
     XX(jl_gc_collect) \
     XX(jl_gc_conservative_gc_support_enabled) \
     XX(jl_gc_counted_calloc) \
@@ -186,6 +187,7 @@
     XX(jl_gc_new_weakref_th) \
     XX(jl_gc_num) \
     XX(jl_gc_pool_alloc) \
+    XX(jl_gc_pool_alloc_instrumented) \
     XX(jl_gc_queue_multiroot) \
     XX(jl_gc_queue_root) \
     XX(jl_gc_safepoint) \

src/llvm-final-gc-lowering.cpp

@@ -205,12 +205,13 @@ Value *FinalLowerGC::lowerQueueGCBinding(CallInst *target, Function &F)
 Value *FinalLowerGC::lowerGCAllocBytes(CallInst *target, Function &F)
 {
     ++GCAllocBytesCount;
-    assert(target->arg_size() == 2);
+    assert(target->arg_size() == 3);
     CallInst *newI;
 
     IRBuilder<> builder(target);
     builder.SetCurrentDebugLocation(target->getDebugLoc());
     auto ptls = target->getArgOperand(0);
+    auto type = target->getArgOperand(2);
     Attribute derefAttr;
 
     if (auto CI = dyn_cast<ConstantInt>(target->getArgOperand(1))) {
@@ -221,19 +222,19 @@ Value *FinalLowerGC::lowerGCAllocBytes(CallInst *target, Function &F)
         if (offset < 0) {
             newI = builder.CreateCall(
                 bigAllocFunc,
-                { ptls, ConstantInt::get(getSizeTy(F.getContext()), sz + sizeof(void*)) });
+                { ptls, ConstantInt::get(getSizeTy(F.getContext()), sz + sizeof(void*)), type });
             derefAttr = Attribute::getWithDereferenceableBytes(F.getContext(), sz + sizeof(void*));
         }
         else {
             auto pool_offs = ConstantInt::get(Type::getInt32Ty(F.getContext()), offset);
             auto pool_osize = ConstantInt::get(Type::getInt32Ty(F.getContext()), osize);
-            newI = builder.CreateCall(poolAllocFunc, { ptls, pool_offs, pool_osize });
+            newI = builder.CreateCall(poolAllocFunc, { ptls, pool_offs, pool_osize, type });
             derefAttr = Attribute::getWithDereferenceableBytes(F.getContext(), osize);
         }
     } else {
         auto size = builder.CreateZExtOrTrunc(target->getArgOperand(1), getSizeTy(F.getContext()));
         size = builder.CreateAdd(size, ConstantInt::get(getSizeTy(F.getContext()), sizeof(void*)));
-        newI = builder.CreateCall(allocTypedFunc, { ptls, size, ConstantPointerNull::get(Type::getInt8PtrTy(F.getContext())) });
+        newI = builder.CreateCall(allocTypedFunc, { ptls, size, type });
         derefAttr = Attribute::getWithDereferenceableBytes(F.getContext(), sizeof(void*));
     }
     newI->setAttributes(newI->getCalledFunction()->getAttributes());

src/llvm-late-gc-lowering.cpp

@@ -2324,22 +2324,6 @@ bool LateLowerGCFrame::CleanupIR(Function &F, State *S, bool *CFGModified) {
                 IRBuilder<> builder(CI);
                 builder.SetCurrentDebugLocation(CI->getDebugLoc());
 
-                // Create a call to the `julia.gc_alloc_bytes` intrinsic, which is like
-                // `julia.gc_alloc_obj` except it doesn't set the tag.
-                auto allocBytesIntrinsic = getOrDeclare(jl_intrinsics::GCAllocBytes);
-                auto ptlsLoad = get_current_ptls_from_task(builder, CI->getArgOperand(0), tbaa_gcframe);
-                auto ptls = builder.CreateBitCast(ptlsLoad, Type::getInt8PtrTy(builder.getContext()));
-                auto newI = builder.CreateCall(
-                    allocBytesIntrinsic,
-                    {
-                        ptls,
-                        builder.CreateIntCast(
-                            CI->getArgOperand(1),
-                            allocBytesIntrinsic->getFunctionType()->getParamType(1),
-                            false)
-                    });
-                newI->takeName(CI);
-
                 // LLVM alignment/bit check is not happy about addrspacecast and refuse
                 // to remove write barrier because of it.
                 // We pretty much only load using `T_size` so try our best to strip
@@ -2378,7 +2362,36 @@ bool LateLowerGCFrame::CleanupIR(Function &F, State *S, bool *CFGModified) {
                         builder.CreateAlignmentAssumption(DL, tag, 16);
                     }
                 }
-                // Set the tag.
+
+                // Create a call to the `julia.gc_alloc_bytes` intrinsic, which is like
+                // `julia.gc_alloc_obj` except it specializes the call based on the constant
+                // size of the object to allocate, to save one indirection, and doesn't set
+                // the type tag. (Note that if the size is not a constant, it will call
+                // gc_alloc_obj, and will redundantly set the tag.)
+                auto allocBytesIntrinsic = getOrDeclare(jl_intrinsics::GCAllocBytes);
+                auto ptlsLoad = get_current_ptls_from_task(builder, CI->getArgOperand(0), tbaa_gcframe);
+                auto ptls = builder.CreateBitCast(ptlsLoad, Type::getInt8PtrTy(builder.getContext()));
+                auto newI = builder.CreateCall(
+                    allocBytesIntrinsic,
+                    {
+                        ptls,
+                        builder.CreateIntCast(
+                            CI->getArgOperand(1),
+                            allocBytesIntrinsic->getFunctionType()->getParamType(1),
+                            false),
+                        builder.CreatePtrToInt(tag, T_size),
+                    });
+                newI->takeName(CI);
+
+                // Now, finally, set the tag. We do this in IR instead of in the C alloc
+                // function, to provide possible optimization opportunities. (I think? TBH
+                // the most recent editor of this code is not entirely clear on why we
+                // prefer to set the tag in the generated code. Providing optimziation
+                // opportunities is the most likely reason; the tradeoff is slightly
+                // larger code size and increased compilation time, compiling this
+                // instruction at every allocation site, rather than once in the C alloc
+                // function.)
+                auto &M = *builder.GetInsertBlock()->getModule();
                 StoreInst *store = builder.CreateAlignedStore(
                     tag, EmitTagPtr(builder, tag_type, newI), Align(sizeof(size_t)));
                 store->setOrdering(AtomicOrdering::Unordered);

src/llvm-pass-helpers.cpp

@@ -120,6 +120,12 @@ namespace jl_intrinsics {
     static const char *QUEUE_GC_ROOT_NAME = "julia.queue_gc_root";
     static const char *QUEUE_GC_BINDING_NAME = "julia.queue_gc_binding";
 
+    static auto T_size_t(const JuliaPassContext &context) {
+        return sizeof(size_t) == sizeof(uint32_t) ?
+            Type::getInt32Ty(context.getLLVMContext()) :
+            Type::getInt64Ty(context.getLLVMContext());
+    }
+
     // Annotates a function with attributes suitable for GC allocation
     // functions. Specifically, the return value is marked noalias and nonnull.
     // The allocation size is set to the first argument.
@@ -150,9 +156,8 @@ namespace jl_intrinsics {
                 FunctionType::get(
                     context.T_prjlvalue,
                     { Type::getInt8PtrTy(context.getLLVMContext()),
-                        sizeof(size_t) == sizeof(uint32_t) ?
-                        Type::getInt32Ty(context.getLLVMContext()) :
-                        Type::getInt64Ty(context.getLLVMContext()) },
+                        T_size_t(context),
+                        T_size_t(context) }, // type
                     false),
                 Function::ExternalLinkage,
                 GC_ALLOC_BYTES_NAME);
@@ -227,12 +232,18 @@ namespace jl_intrinsics {
 }
 
 namespace jl_well_known {
-    static const char *GC_BIG_ALLOC_NAME = XSTR(jl_gc_big_alloc);
-    static const char *GC_POOL_ALLOC_NAME = XSTR(jl_gc_pool_alloc);
+    static const char *GC_BIG_ALLOC_NAME = XSTR(jl_gc_big_alloc_instrumented);
+    static const char *GC_POOL_ALLOC_NAME = XSTR(jl_gc_pool_alloc_instrumented);
     static const char *GC_QUEUE_ROOT_NAME = XSTR(jl_gc_queue_root);
     static const char *GC_QUEUE_BINDING_NAME = XSTR(jl_gc_queue_binding);
     static const char *GC_ALLOC_TYPED_NAME = XSTR(jl_gc_alloc_typed);
 
+    static auto T_size_t(const JuliaPassContext &context) {
+        return sizeof(size_t) == sizeof(uint32_t) ?
+            Type::getInt32Ty(context.getLLVMContext()) :
+            Type::getInt64Ty(context.getLLVMContext());
+    }
+
     using jl_intrinsics::addGCAllocAttributes;
 
     const WellKnownFunctionDescription GCBigAlloc(
@@ -242,9 +253,8 @@ namespace jl_well_known {
                 FunctionType::get(
                     context.T_prjlvalue,
                     { Type::getInt8PtrTy(context.getLLVMContext()),
-                        sizeof(size_t) == sizeof(uint32_t) ?
-                        Type::getInt32Ty(context.getLLVMContext()) :
-                        Type::getInt64Ty(context.getLLVMContext()) },
+                        T_size_t(context),
+                        T_size_t(context) },
                     false),
                 Function::ExternalLinkage,
                 GC_BIG_ALLOC_NAME);
@@ -258,7 +268,7 @@ namespace jl_well_known {
             auto poolAllocFunc = Function::Create(
                 FunctionType::get(
                     context.T_prjlvalue,
-                    { Type::getInt8PtrTy(context.getLLVMContext()), Type::getInt32Ty(context.getLLVMContext()), Type::getInt32Ty(context.getLLVMContext()) },
+                    { Type::getInt8PtrTy(context.getLLVMContext()), Type::getInt32Ty(context.getLLVMContext()), Type::getInt32Ty(context.getLLVMContext()), T_size_t(context) },
                     false),
                 Function::ExternalLinkage,
                 GC_POOL_ALLOC_NAME);
@@ -301,10 +311,8 @@ namespace jl_well_known {
                 FunctionType::get(
                     context.T_prjlvalue,
                     { Type::getInt8PtrTy(context.getLLVMContext()),
-                        sizeof(size_t) == sizeof(uint32_t) ?
-                        Type::getInt32Ty(context.getLLVMContext()) :
-                        Type::getInt64Ty(context.getLLVMContext()),
-                        Type::getInt8PtrTy(context.getLLVMContext()) },
+                        T_size_t(context),
+                        T_size_t(context) }, // type
                     false),
                 Function::ExternalLinkage,
                 GC_ALLOC_TYPED_NAME);