Re: [lockup] Re: objrmap-core-1 (rmap removal for file mappings to avoid 4:4 in <=16G machines)

[Ingo Molnar]

* Andrew Morton <akpm@xxxxxxxx> wrote:

> > or run the attached test-mmap2.c code, which simulates a very small DB
> >  app using only 1800 vmas per process: it only maps 8 MB of shm and
> >  spawns 32 processes. This has an even more lethal effect than the
> >  previous code.
> 
> Do these tests actually make any forward progress at all, or is it some bug
> which has sent the kernel into a loop?

i think they make a forward progress so it's more of a DoS - but a very
effective one, especially considering that i didnt even try hard ...

what worries me is that there are apps that generate such vma patterns
(for various reasons).

I do believe that scanning ->i_mmap & ->i_mmap_shared is fundamentally
flawed.

	Ingo
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