Re: can you switch between GFP_ATOMIC and GFP_KERNEL?

[Roland Dreier <roland@topspin.com>]

    Michael> My question is, new sk_buffs are always allocated with
    Michael> GFP_KERNEL and can be swapped out. Is it possible to
    Michael> change the allocation status of already-allocated memory
    Michael> to GFP_ATOMIC on the fly? (i.e. both the slab-cache
    Michael> sk_buff header memory as well as the kmalloc'd data
    Michael> area).

This question is ill-posed -- kernel memory can never be swapped out,
whether it's allocated with GFP_KERNEL or GFP_ATOMIC.  The difference
between GFP_KERNEL and GFP_ATOMIC is whether the actual allocation can
sleep, that is:

	foo = kmalloc(sizeof foo, GFP_ATOMIC);	/* will not sleep */
	foo = kmalloc(sizeof foo, GFP_KERNEL);	/* can sleep */

However, whichever gfp flags are used to allocate memory, the memory
is the same once the allocation is done.  Neither kmalloc'ed memory
nor sk_buffs will ever be swapped.

 - Roland