Modern Linux memory management

[ik]

On Thu, Jan 26, 2012 at 18:08, Yedidyah Bar-David <
linux-il at didi.bardavid.org> wrote:

> On Thu, Jan 26, 2012 at 10:54:56AM -0500, Ori Berger wrote:
> > On 01/26/2012 10:16 AM, Baruch Siach wrote:
> >
> > >>Only by using valgrind, that I could find the exact location and figure
> > >>out, that it was another function that had the problem.
> > >>
> > >>How does the modern memory management system is working then, that it
> takes
> > >>so much time for the problem to surface ?
> > >
> > >Now, if you corrupt the internal glibc data structure, glibc won't
> notice
> > >until you try to call one of malloc(), free(), etc.
> >
> > And in addition to what Baruch said:
> >
> > Valgrind will always catch these errors, but will result in
> > significant slowdown (x10-x20). There are tools like DUMA (and its
> > earlier incarnation, Electric Fence) incur almost no CPU overhead
> > and can detect many kinds of corruptions as soon as they happen, by
> > using the memory management units.
> >
> > (Because of the MMU granularity, you need to run your program twice
> > - one in which allocations are aligned to the lower address, and one
> > when they are aligned to the top address)
> >
> > There is also a middle ground; gcc's mudflap
> > <http://www.stlinux.com/devel/debug/mudflap> and -- if your program
> > is pure C and can be compiled by tcc,
> > <http://bellard.org/tcc/tcc-doc.html#SEC21>; These are comparable to
> > valgrind in functionality (for code you compile with them; standard
> > library code runs at full speed/unchecked), but usually only
> > introduce a small slowdown (10% or so).
>
> BTW, in case you do not know Fabric Bellard, he does lots of very cool
> stuff - he is the author of qemu, and every now and then I give a look
> at his site. I now did because of this post and found out an amazing
> project of a PC Emulator in Javascript:
> http://bellard.org/jslinux/
> The guy is simply amazing.
> --
> Didi
>

Thank you all, you made me wiser :)

Ido

>
>
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