[all-commits] [llvm/llvm-project] 643bf6: [scudo] Add partial chunk heuristic to retrieval a...

Joshua Baehring via All-commits all-commits at lists.llvm.org
Mon Aug 26 10:45:00 PDT 2024


  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 643bf6cb01bc3faa54c5510c904ea3bdcb4bf42f
      https://github.com/llvm/llvm-project/commit/643bf6cb01bc3faa54c5510c904ea3bdcb4bf42f
  Author: Joshua Baehring <98630690+JoshuaMBa at users.noreply.github.com>
  Date:   2024-08-26 (Mon, 26 Aug 2024)

  Changed paths:
    M compiler-rt/lib/scudo/standalone/secondary.h
    M compiler-rt/lib/scudo/standalone/tests/secondary_test.cpp

  Log Message:
  -----------
  [scudo] Add partial chunk heuristic to retrieval algorithm. (#105009)

Previously the secondary cache retrieval algorithm would not allow
retrievals of memory chunks where the number of unused bytes would be
greater than than `MaxUnreleasedCachePages * PageSize` bytes. This meant
that even if a memory chunk satisfied the requirements of the optimal
fit algorithm, it may not be returned. This remains true if memory
tagging is enabled. However, if memory tagging is disabled, a new
heuristic has been put in place. Specifically, If a memory chunk is a
non-optimal fit, the cache retrieval algorithm will attempt to release
the excess memory to force a cache hit while keeping RSS down.

In the event that a memory chunk is a non-optimal fit, the retrieval
algorithm will release excess memory as long as the amount of memory to
be released is less than or equal to 4 Pages. If the amount of memory to
be released exceeds 4 Pages, the retrieval algorithm will not consider
that cached memory chunk valid for retrieval.

This change also addresses an alignment issue in a test case submitted
in #104807.



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