Messages in this thread | | | Date | Tue, 26 Jun 2007 20:33:05 -0700 (PDT) | From | Davide Libenzi <> | Subject | Re: [patch 2/3] MAP_NOZERO - implement sys_brk2() |
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On Tue, 26 Jun 2007, Rik van Riel wrote:
> Davide Libenzi wrote: > > The following patch implements the sys_brk2() syscall, that nothing is > > other than a sys_brk() with an extra "flags" parameter. This can be used > > to pass the new MAP_NOZERO bit, to ask the kernel to hand over non-zero > > pages if possible. > > Since programs can get back free()d memory after a malloc(), > with the old contents of the memory intact, surely your > MAP_NONZERO behavior could be the default for programs that > can get away with it? > > Maybe we could use some magic ELF header, similar to the > way non-executable stack is handled?
Well, the quick&ugly glibc patch simply uses an environment variable, just because I wanted to bench the kernel build with using the same glibc+gcc. Yes, it can be the default behaviour for the allocator. The patch handles calloc() correctly, by forcibly zeroing memory in such calls. But other software must be taught too, to use MAP_NOZERO when they do not need zeroed memory. I did that for the gcc garbage collector.
- Davide
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