Re: MAX_ARG_PAGES has no effect?

[Andi Kleen <ak@suse.de>]

On Thursday 01 September 2005 08:57, Ingo Molnar wrote:

> the whole thing should be reworked, so that there is no artificial limit
> like MAX_ARG_PAGES. (it is after all just another piece of memory, in
> theory)

Yes, a sysctl would probably lead to fragmentation problems and then
people would do ugly linked lists of buffers like poll.

> If we do unconditional page-flipping then we fragment the argument
> space, if we do both page-flipping if things are unfragmented and
> well-aligned, and 'compact' the layout otherwise, we havent solved the
> problem and have introduced a significant extra layer of complexity to
> an already security-sensitive and fragile piece of code.

Page flipping = COW like fork would do?

Not sure how this would work - the arguments of execve can be anywhere
in the address space and would presumably be often be in a inconvenient
place like in the middle of the stack of the new executable.

> The best method i found was to get rid of bprm->pages[] and to directly
> copy strings into the new mm via kmap (and to follow whatever RAM
> allocation policies/limits there are for the new mm), but that's quite
> ugly.

That sounds better.

-Andi