When building Scylla with ThinLTO enabled (default with Clang), the linker
spawns threads equal to the number of CPU cores during linking. This high
parallelism can cause out-of-memory (OOM) issues in CI environments,
potentially freezing the build host or triggering the OOM killer.
In this change:
1. Rename `LINK_MEM_PER_JOB` to `Scylla_RAM_PER_LINK_JOB` and make it
user-configurable
2. Add `Scylla_PARALLEL_LINK_JOBS` option to directly control concurrent
link jobs (useful for hosts with large RAM)
3. Increase the default value of `Scylla_PARALLEL_LINK_JOBS` to 16 GiB
when LTO is enabled
4. Default to 2 parallel link jobs when LTO is enabled if the calculated
number if less than 2 for faster build.
Notes:
- Host memory is shared across job pools, so pool separation alone doesn't help
- Ninja lacks per-job memory quota support
- Only affects link parallelism in LTO-enabled builds
See
https://clang.llvm.org/docs/ThinLTO.html#controlling-backend-parallelismFixesscylladb/scylladb#22275
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#22383
6e1fb2c74e