Re: [RFC 4/9] Atomic reclaim: Save irq flags in vmscan.c

Christoph Lameter
2007-08-14T22:20:47Z

On Tue, 14 Aug 2007, Andi Kleen wrote:

> > Could you be a bit more specific? Where do you want to place the data?
>
> DEFINE_PER_CPU(int, zone_flag);
>
> get_cpu(); // likely already true and then not needed
> __get_cpu(zone_flag) = 1;
> /* wmb is implied in spin_lock I think */

No its not. Only on x64 which has implicit write ordering.

> spin_lock(&zone->lru_lock);
> ...
> spin_unlock(&zone->lru_lock);
> __get_cpu(zone_flag) = 0;
> put_cpu();
>
> Interrupt handler
>
> if (!__get_cpu(zone_flag)) {

There are more spinlocks needed. So we would just check the whole bunch
and fail if any of them are used?

> do things with zone locks
> }
>
> The interrupt handler shouldn't touch zone_flag. If it wants
> to it would need to be converted to a local_t and incremented/decremented
> (should be about the same cost at least on architectures with sane
> local_t implementation)

That would mean we need to fork the code for reclaim?