Re: [PATCH] Inconsistent mmap()/mremap() flags

Hugh Dickins
2007-10-02T12:19:49Z

On Tue, 2 Oct 2007, Thayne Harbaugh wrote:
> On Tue, 2007-10-02 at 07:15 +0200, Andi Kleen wrote:
>
> > For mmap you can emulate it by passing a low hint != 0 (e.g. getpagesize())
> > in address but without MAP_FIXED and checking if the result is not beyond
> > your range.
>
> Cool. That's a much better solution for multiple reasons - like you
> mention, MAP_32BIT is only 2GB as well as it's only available on x86_64.
>
> > > > Given for mremap() it is not that easy because there is no "hint" argument
> > > > without MREMAP_FIXED; but unless someone really needs it i would prefer
> > > > to not propagate the hack. If it's really needed it's probably better
> > > > to implement a start search hint for mremap()

I think you can do it already, without us complicating mremap further
with such a start search hint.

First call mmap with a low hint address, the new size you'll be wanting
from the mremap, PROT_NONE, MAP_ANONYMOUS, -1, 0. Then call mremap with
old address, old size, new size, MREMAP_MAYMOVE|MREMAP_FIXED, and new
address as returned by the preparatory mmap.

Hugh