Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures

On Thu, Aug 16, 2007 at 10:11:05AM +0800, Herbert Xu wrote:

On Thu, Aug 16, 2007 at 12:05:56PM +1000, Paul Mackerras wrote:

quoted

Herbert Xu writes:

quoted

See sk_stream_mem_schedule in net/core/stream.c:

        /* Under limit. */
        if (atomic_read(sk->sk_prot->memory_allocated) < sk->sk_prot->sysctl_mem[0]) {
                if (*sk->sk_prot->memory_pressure)
                        *sk->sk_prot->memory_pressure = 0;
                return 1;
        }

        /* Over hard limit. */
        if (atomic_read(sk->sk_prot->memory_allocated) > sk->sk_prot->sysctl_mem[2]) {
                sk->sk_prot->enter_memory_pressure();
                goto suppress_allocation;
        }

We don't need to reload sk->sk_prot->memory_allocated here.

Are you sure?  How do you know some other CPU hasn't changed the value
in between?

Yes I'm sure, because we don't care if others have increased
the reservation.

Note that even if we did we'd be using barriers so volatile
won't do us any good here.

If the load-coalescing is important to performance, why not load into
a local variable?

						Thanx, Paul