df0a9badc6
means that the dynamic linker gets mapped in at the top of available user virtual memory (typically just below the stack), shared libraries get mapped downwards from that point, and calls to mmap() that don't specify a preferred address will get mapped in below those. This means that the heap and the mmap()ed allocations will grow towards each other, allowing one or the other to grow larger than before. Previously, the heap was limited to MAXDSIZ by the placement of the dynamic linker (and the process's rlimits) and the space available to mmap was hobbled by this reservation. This is currently only enabled via an *option* for the i386 platform (though other platforms are expected to follow). Add "options USE_TOPDOWN_VM" to your kernel config file, rerun config, and rebuild your kernel to take advantage of this. Note that the pmap_prefer() interface has not yet been modified to play nicely with this, so those platforms require a bit more work (most notably the sparc) before they can use this new memory arrangement. This change also introduces a VM_DEFAULT_ADDRESS() macro that picks the appropriate default address based on the size of the allocation or the size of the process's text segment accordingly. Several drivers and the SYSV SHM address assignment were changed to use this instead of each one picking their own "default". |
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