[CSSPGO] Adjust SampleContextFrameVector to be a shorter SmallVector

[hoy]

Summary

It appears that some memory saving can be archived by tweaking the existing SampleContextFrameVector setup. Below are memory usage for two benchmarks before and after this change.

1. Medium benchmark:
   • Before:

note: After computeSizeForProfiledFunctions
note: VM: 12.50 GB   RSS: 11.02 GB
note: After generateProbeBasedProfile
note: **VM: 30.56 GB   RSS: 29.08 GB**
note: After postProcessProfiles
note: VM: 31.91 GB   RSS: 30.43 GB

• After:

note: After computeSizeForProfiledFunctions
note: VM: 12.26 GB   RSS: 10.80 GB
note: After generateProbeBasedProfile
note: **VM: 28.76 GB   RSS: 27.29 GB**
note: After postProcessProfiles
note: VM: 30.12 GB   RSS: 28.66 GB

2. Large benchmark:
   • Before:

note: After computeSizeForProfiledFunctions
note: VM: 106.28 GB   RSS: 91.25 GB
note: After generateProbeBasedProfile
note: **VM: 245.19 GB   RSS: 224.30 GB**
note: After postProcessProfiles
note: VM: 254.96 GB   RSS: 221.58 GB

• After:

note: After computeSizeForProfiledFunctions
note: VM: 105.95 GB   RSS: 91.04 GB
note: After generateProbeBasedProfile
note: VM: **234.29 GB   RSS: 215.39 GB**
note: After postProcessProfiles
note: VM: 244.03 GB   RSS: 213.45 GB

[wenlei]

Does this lengthen process time?

[hoy]

In D118203#3271143, @wenlei wrote:

Does this lengthen process time?

Not necessarily if reallocaton happens frequently.

Before:

note: After computeSizeForProfiledFunctions
note: Tue Jan 25 10:38:10 2022
note: VM: 106.28 GB   RSS: 91.25 GB
note: After generateProbeBasedProfile
note: Tue Jan 25 11:06:02 2022
note: VM: 245.19 GB   RSS: 224.30 GB

After:

note: After computeSizeForProfiledFunctions
note: Tue Jan 25 15:31:13 2022
note: VM: 105.95 GB   RSS: 91.04 GB
note: After generateProbeBasedProfile
note: Tue Jan 25 15:58:03 2022
note: VM: 234.29 GB   RSS: 215.39 GB

[wenlei]

In D118203#3271163, @hoy wrote:

In D118203#3271143, @wenlei wrote:

Does this lengthen process time?

Not necessarily if reallocaton happens frequently.

Before:

note: After computeSizeForProfiledFunctions
note: Tue Jan 25 10:38:10 2022
note: VM: 106.28 GB   RSS: 91.25 GB
note: After generateProbeBasedProfile
note: Tue Jan 25 11:06:02 2022
note: VM: 245.19 GB   RSS: 224.30 GB

After:

note: After computeSizeForProfiledFunctions
note: Tue Jan 25 15:31:13 2022
note: VM: 105.95 GB   RSS: 91.04 GB
note: After generateProbeBasedProfile
note: Tue Jan 25 15:58:03 2022
note: VM: 234.29 GB   RSS: 215.39 GB

Thanks for checking. Nice improvements!

llvm/include/llvm/ProfileData/SampleProf.h

struct SampleContextFrame {
   }
 };
 
 static inline hash_code hash_value(const SampleContextFrame &arg) {
   return hash_combine(arg.CallerName, arg.Callsite.LineOffset,
                       arg.Callsite.Discriminator);
 }
 
-using SampleContextFrameVector = SmallVector<SampleContextFrame, 10>;
+using SampleContextFrameVector = SmallVector<SampleContextFrame, 1>;
 using SampleContextFrames = ArrayRef<SampleContextFrame>;
 
 struct SampleContextFrameHash {
   uint64_t operator()(const SampleContextFrameVector &S) const {
     return hash_combine_range(S.begin(), S.end());
   }
 };