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diff --git a/docs/ThinLTO.rst b/docs/ThinLTO.rst index d417febda502..31fff51a61e9 100644 --- a/docs/ThinLTO.rst +++ b/docs/ThinLTO.rst @@ -126,6 +126,50 @@ which currently must be enabled through a linker option. - lld (as of LLVM r296702): ``-Wl,--thinlto-cache-dir=/path/to/cache`` +Cache Pruning +------------- + +To help keep the size of the cache under control, ThinLTO supports cache +pruning. Cache pruning is supported with ld64 and ELF lld, but currently only +ELF lld allows you to control the policy with a policy string. The cache +policy must be specified with a linker option. + +- ELF lld (as of LLVM r298036): + ``-Wl,--thinlto-cache-policy,POLICY`` + +A policy string is a series of key-value pairs separated by ``:`` characters. +Possible key-value pairs are: + +- ``cache_size=X%``: The maximum size for the cache directory is ``X`` percent + of the available space on the the disk. Set to 100 to indicate no limit, + 50 to indicate that the cache size will not be left over half the available + disk space. A value over 100 is invalid. A value of 0 disables the percentage + size-based pruning. The default is 75%. + +- ``cache_size_bytes=X``, ``cache_size_bytes=Xk``, ``cache_size_bytes=Xm``, + ``cache_size_bytes=Xg``: + Sets the maximum size for the cache directory to ``X`` bytes (or KB, MB, + GB respectively). A value over the amount of available space on the disk + will be reduced to the amount of available space. A value of 0 disables + the byte size-based pruning. The default is no byte size-based pruning. + + Note that ThinLTO will apply both size-based pruning policies simultaneously, + and changing one does not affect the other. For example, a policy of + ``cache_size_bytes=1g`` on its own will cause both the 1GB and default 75% + policies to be applied unless the default ``cache_size`` is overridden. + +- ``prune_after=Xs``, ``prune_after=Xm``, ``prune_after=Xh``: Sets the + expiration time for cache files to ``X`` seconds (or minutes, hours + respectively). When a file hasn't been accessed for ``prune_after`` seconds, + it is removed from the cache. A value of 0 disables the expiration-based + pruning. The default is 1 week. + +- ``prune_interval=Xs``, ``prune_interval=Xm``, ``prune_interval=Xh``: + Sets the pruning interval to ``X`` seconds (or minutes, hours + respectively). This is intended to be used to avoid scanning the directory + too often. It does not impact the decision of which files to prune. A + value of 0 forces the scan to occur. The default is every 20 minutes. + Clang Bootstrap --------------- |