[PATCH] D116367: [ELF][LTO] --thinlto-index-only: call madvise(MADV_DONTNEED)

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
Herald added subscribers: arphaman, arichardson, inglorion, emaste.
MaskRay requested review of this revision.
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@tejohnson noticed that freeing MemoryBuffer instances right before
`lto->compile` can save RSS.

Symbol and section names are backed by MemoryBuffer, so simply destroying
MemoryBuffer would make some infrequent passes (parseSymbolVersion,
reportBackrefs) crash and make debugging difficult. This patch leverages
madvise(MADV_DONTNEED) which hieve the major gain without the latent issues.

`Maximum resident set size (kbytes): ` for a large --thinlto-index-only link:

- current behavior: 10146104
- destroy MemoryBuffer instances: 8555240
- madvise(MADV_DONTNEED): 8739796

Based on D116366 <https://reviews.llvm.org/D116366>


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D116367

Files:
  lld/ELF/Driver.cpp
  lld/ELF/Driver.h
  lld/ELF/InputFiles.cpp
  lld/ELF/InputFiles.h

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