Re: [PATCH v2 1/7] modules: Create rlimit for module space

Edgecombe, Rick P
2018-10-13T00:04:14Z

On Fri, 2018-10-12 at 19:22 +0200, Jann Horn wrote:
> On Fri, Oct 12, 2018 at 7:04 PM Edgecombe, Rick P
> <rick.p.edgecombe@intel.com> wrote:
> > On Fri, 2018-10-12 at 02:35 +0200, Jann Horn wrote:
> > > Why all the rbtree stuff instead of stashing a pointer in struct
> > > vmap_area, or something like that?
> >
> > Since the tracking was not for all vmalloc usage, the intention was to not
> > bloat
> > the structure for other usages likes stacks. I thought usually there
> > wouldn't be
> > nearly as much module space allocations as there would be kernel stacks, but
> > I
> > didn't do any actual measurements on the tradeoffs.
>
> I imagine that one extra pointer in there - pointing to your struct
> mod_alloc_user - would probably not be terrible. 8 bytes more per
> kernel stack shouldn't be so bad?

I looked into this and it starts to look a little messy. The nommu.c version of
vmalloc doesn't use or expose access to vmap_area or vm_struct. So it starts to
look like a bunch of IFDEFs to remove the rlimit in the nommu case or making a
stand in that maintains pretend vm struct's in nommu.c. I had actually
previously tried to at least pull the allocations size from vmalloc structs, but it broke on nommu.

Thought I would check back and see. How important do you think this is?