60 lines
2.1 KiB
Plaintext
60 lines
2.1 KiB
Plaintext
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Notes about the Chrome memory allocator.
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Background
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We use this library as a generic way to fork into any of several allocators.
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Currently we can, at runtime, switch between:
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the default windows allocator
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the windows low-fragmentation-heap
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tcmalloc
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jemalloc (the heap used most notably within Mozilla Firefox)
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The mechanism for hooking LIBCMT in windows is rather tricky. The core
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problem is that by default, the windows library does not declare malloc and
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free as weak symbols. Because of this, they cannot be overriden. To work
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around this, we start with the LIBCMT.LIB, and manually remove all allocator
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related functions from it using the visual studio library tool. Once removed,
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we can now link against the library and provide custom versions of the
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allocator related functionality.
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Source code
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-----------
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This directory contains just the allocator (i.e. shim) layer that switches
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between the different underlying memory allocation implementations.
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The tcmalloc and jemalloc libraries originate outside of Chromium
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and exist in ../../third_party/tcmalloc and ../../third_party/jemalloc
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(currently, the actual locations are defined in the allocator.gyp file).
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The third party sources use a vendor-branch SCM pattern to track
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Chromium-specific changes independently from upstream changes.
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The general intent is to push local changes upstream so that over
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time we no longer need any forked files.
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Adding a new allocator
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----------------------
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Adding a new allocator requires definition of the following five functions:
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extern "C" {
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bool init();
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void* malloc(size_t s);
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void* realloc(void* p, size_t s);
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void free(void* s);
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size_t msize(void* p);
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}
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All other allocation related functions (new/delete/calloc/etc) have been
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implemented generically to work across all allocators.
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Usage
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-----
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You can use the different allocators by setting the environment variable
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CHROME_ALLOCATOR to:
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"tcmalloc" - TC Malloc (default)
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"jemalloc" - JE Malloc
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"winheap" - Windows default heap
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"winlfh" - Windows Low-Fragmentation heap
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