Hello,

Appreciate the swift responses.

I need this feature in GHC 8.10.7. This, I believe is only available post
9.10. I can try replicating the same kind of behavior in GHC 8.10.7.

Some more context to the problem at hand:

The overhead of the profiling I want to enable should be as minimal as possible
as we plan to run this build in production.
The memory leak I'm trying to debug happens over a few days after over a million
requests and we aren't able to replicate it offline.

I can take inspiration from the work done in 9.10 and replicate it in 8.10.7 in
a way that it can be used without other features of profiling.

This is what I was trying to do. Ie. Add a new field "era" in the "StgHeader"
instead of "StgProfHeader". Making the follow-up changes was the problem as I
might've missed the bookkeeping in a few places. But now I can look at 9.10. So
I have a baseline to compare with.

I will try this, and get back to this thread.

Best,
Adithya

On Sun, Feb 25, 2024 at 9:33 PM Rodrigo Mesquita <rodrigo.m.mesquita@gmail.com> wrote:
Hello Adithya,

This sounds just like what has been implemented as the default mode for eras profiling: https://well-typed.com/blog/2024/01/ghc-eras-profiling — which tracks an “era” for each heap object — and, by default, uses a major garbage collection as the increment trigger.
Could you check it out and see if it would supersede what you are trying to do?

Cheers,
Rodrigo

On 25 Feb 2024, at 12:58, Adithya Kumar <adi.obilisetty@gmail.com> wrote:

Hello,

I want to add a field for collecting information about the number of GCs a
particular heap object survived.

I've done the following to implement this:
- Add a field "StgWord gc_id" to struct "StgHeader" and "StgThunkHeader"
- Update "SET_HDR" macro in "ClosureMacros.h" to update the "gc_id"
- Update the "closureTypeHeaderSize" function in "Heap/ClosureTypes.hs" to
  account for that 1 extra word.

Compilation leads to a segmentation fault. The stage 2 compiler is built. But
usage of it leads to a segmentation fault.

Build output:
```
chmod +x                                                     inplace/bin/ghc-stage2
"inplace/bin/ghc-stage2" -hisuf dyn_hi -osuf  dyn_o -hcsuf dyn_hc -fPIC -dynamic  -O0 -H64m -Wall      -hide-all-packages -package-env - -i -iutils/check-api-annotations/. -iutils/check-api-annotations/dist-install/build -Iutils/check-api-annotations/dist-install/build -iutils/check-api-annotations/dist-install/build/check-api-annotations/autogen -Iutils/check-api-annotations/dist-install/build/check-api-annotations/autogen     -optP-include -optPutils/check-api-annotations/dist-install/build/check-api-annotations/autogen/cabal_macros.h -package-id Cabal-3.2.1.0 -package-id base-4.14.3.0 -package-id containers-0.6.5.1 -package-id directory-1.3.6.0 -package-id ghc-8.10.7.20240224 -Wall -XHaskell2010  -no-user-package-db -rtsopts       -Wnoncanonical-monad-instances  -outputdir utils/check-api-annotations/dist-install/build   -c utils/check-api-annotations/./Main.hs -o utils/check-api-annotations/dist-install/build/Main.dyn_o
utils/check-api-annotations/ghc.mk:18: recipe for target 'utils/check-api-annotations/dist-install/build/Main.dyn_o' failed
make[1]: *** [utils/check-api-annotations/dist-install/build/Main.dyn_o] Segmentation fault (core dumped)
Makefile:123: recipe for target 'all' failed
make: *** [all] Error 2
```

Is there any other place I've missed follow-up modifications?

I appreciate any help provided.

Best,
Adithya
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