Hello,
On Mon, Jan 30, 2012 at 11:58:52AM -0600, Christoph Lameter wrote:
No, NULL is never gonna be a valid return from any allocator including percpu. Percpu allocator doesn't and will never do so.
How do you prevent the percpu allocator from returning NULL? I thought the per cpu offsets can wrap around?
I thought it didn't. I rememer thinking about this and determining that NULL can't be allocated for dynamic addresses. Maybe I'm imagining things. Anyways, if it can return NULL for valid allocation, it is a bug and should be fixed.
I'm saying we don't have this for ZERO_SIZE_PTR in any meaningful way at this point. If somebody wants to implement it properly, please feel free to, but simply applying ZERO_SIZE_PTR without other changes doesn't make any sense.
We have no clean notion of how a percpu pointer needs to be handled. Both ways of handling things have drawbacks.
We don't have returned addr >= PAGE_SIZE guarantee yet but I'm fairly sure that's the only acceptable direction if we want any improvement in this area.
Thanks.