[PATCH] D71975: [Support] Support MF_HUGE_HINT on Linux and FreeBSD

[John Baldwin via Phabricator via llvm-commits]

bsdjhb added a comment.

For FreeBSD, `MAP_ALIGNED_SUPER` probably isn't what you want.  The default mmap() for MAP_ANON on FreeBSD tries to do what `MAP_ALIGNED_SUPER` does if the request is at least one large page in size first, and if that fails to find available address space, falls back to finding any possible virtual addresses (it does the two steps you are doing inside of mmap() itself).  Specifying `MAP_ALIGNED_SUPER` tells mmap() to only try the first pass and fail without trying the second pass, but then the second call to mmap() that you would make as a result would just do both passes anyway.

FreeBSD doesn't currently have a "must-only-use-large-pages-and-never-demote-to-small-pages" flag which is probably what you would want to use here instead.  (We've talked about adding one, but no one has done it to date.)


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https://reviews.llvm.org/D71975