This patch is another step towards updating the code to handle the
32-bit kernels which I have not been regularly testing. This changes
do not really impact the common case I'm expected which is the latest
kernel running on an x86_64 arch.
Until the linux-2.6.31 kernel the x86 arch did not have support for
64-bit atomic operations. Additionally, the new atomic_compat.h support
for this case was wrong because it embedded a spinlock in the atomic
variable which must always and only be 64-bits total. To handle these
32-bit issues we now simply fall back to the --enable-atomic-spinlock
implementation if the kernel does not provide the 64-bit atomic funcs.
The second issue this patch addresses is the DEBUG_KMEM assumption that
there will always be atomic64 funcs available. On 32-bit archs this may
not be true, and actually that's just fine. In that case the kernel will
will never be able to allocate more the 32-bits worth anyway. So just
check if atomic64 funcs are available, if they are not it means this
is a 32-bit machine and we can safely use atomic_t's instead.
Brian Behlendorf
d04c8a563c