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Diffstat (limited to 'boehm-gc/doc/README.environment')
| -rw-r--r-- | boehm-gc/doc/README.environment | 32 |
1 files changed, 31 insertions, 1 deletions
diff --git a/boehm-gc/doc/README.environment b/boehm-gc/doc/README.environment index d1f3b5c053b..97a13dc3e45 100644 --- a/boehm-gc/doc/README.environment +++ b/boehm-gc/doc/README.environment @@ -1,6 +1,6 @@ The garbage collector looks at a number of environment variables which are then used to affect its operation. These are examined only on Un*x-like -platforms. +platforms and win32. GC_INITIAL_HEAP_SIZE=<bytes> - Initial heap size in bytes. May speed up process start-up. @@ -26,6 +26,14 @@ GC_DUMP_REGULARLY - Generate a GC debugging dump GC_dump() on startup if you have a bug to report, but please include only the last complete dump. +GC_BACKTRACES=<n> - Generate n random backtraces (for heap profiling) after + each GC. Collector must have been built with + KEEP_BACK_PTRS. This won't generate useful output unless + most objects in the heap were allocated through debug + allocators. This is intended to be only a statistical + sample; individual traces may be erroneous due to + concurrent heap mutation. + GC_PRINT_ADDRESS_MAP - Linux only. Dump /proc/self/maps, i.e. various address maps for the process, to stderr on every GC. Useful for mapping root addresses to source for deciphering leak @@ -86,6 +94,28 @@ GC_RETRY_SIGNALS, GC_NO_RETRY_SIGNALS - Try to compensate for lost was turned into a runtime flag to enable last-minute work-arounds. +GC_IGNORE_FB[=<n>] - (Win32 only.) Try to avoid treating a mapped + frame buffer as part of the root set. Certain (higher end?) + graphics cards seems to result in the graphics memory mapped + into the user address space as writable memory. + Unfortunately, there seems to be no systematic way to + identify such memory. Setting the environment variable to n + causes the collector to ignore mappings longer than n MB. + The default value of n is currently 15. (This should cover + a 16 MB graphics card, since the mapping appears to be slightly + shorter than all of graphics memory. It will fail if a dll + writes pointers to collectable objects into a data segment + whose length is >= 15MB. Empirically that's rare, but + certainly possible.) WARNING: Security sensitive applications + should probably disable this feature by setting + GC_disallow_ignore_fb, or by building with -DNO_GETENV, + since small values could force collection of reachable + objects, which is conceivably a (difficult to exploit) + security hole. GC_IGNORE_FB values less than 3 MB + are never honored, eliminating this risk for most, + but not all, applications. This feature is likely to disappear + if/when we find a less disgusting "solution". + The following turn on runtime flags that are also program settable. Checked only during initialization. We expect that they will usually be set through other means, but this may help with debugging and testing: |