Messages in this thread | | | From | "Aneesh Kumar K.V" <> | Subject | Re: [PATCH 26/26] x86/mm: allow to have userspace mappings above 47-bits | Date | Fri, 17 Mar 2017 23:23:54 +0530 |
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"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> writes:
> On x86, 5-level paging enables 56-bit userspace virtual address space. > Not all user space is ready to handle wide addresses. It's known that > at least some JIT compilers use higher bits in pointers to encode their > information. It collides with valid pointers with 5-level paging and > leads to crashes. > > To mitigate this, we are not going to allocate virtual address space > above 47-bit by default. > > But userspace can ask for allocation from full address space by > specifying hint address (with or without MAP_FIXED) above 47-bits. > > If hint address set above 47-bit, but MAP_FIXED is not specified, we try > to look for unmapped area by specified address. If it's already > occupied, we look for unmapped area in *full* address space, rather than > from 47-bit window. > > This approach helps to easily make application's memory allocator aware > about large address space without manually tracking allocated virtual > address space. >
So if I have done a successful mmap which returned > 128TB what should a following mmap(0,...) return ? Should that now search the *full* address space or below 128TB ?
-aneesh
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