Re: nommu: handling anonymous mmap clearing in userspace rather than kernel

[David Howells]

Mike Frysinger <vapier.adi@xxxxxxxxx> wrote:

> a workaround: introduce a new no-mmu-only mmap flag MAP_UNINITIALIZE
> to signal to the kernel that it should skip the memset().  this way,
> userspace malloc() can do mmap(MAP_ANONYMOUS|MAP_UNINITIALIZE) to get
> large chunks of memory without affecting any other anonymous mmap()
> call.

I think that's reasonable for NOMMU.  It's not like the process accessing the
uninitialised memory is prevented from accessing anything it wants to anyway.

I would vote that the memset() should only be skipped if requested as there
may be programs that call mmap(MAP_ANONYMOUS) expecting the memory they're
given to be zeroed out.

David


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