Barrett, Brian W wrote:
Jeff and I talked for a while today, and we're pretty sure that as long as
the byte set by the kernel notifier is written before the pages are returned
into the unallocated list, there isn't actually a race condition. It does
mean that every time the page cache is searched, we also have to check the
byte (and likely take a cache miss), but that's not too evil.
However, there's still then the problem with the notifier concept of how the
kernel passes which pages were given back to the kernel. It has to pass a
(potentially very large) amount of data back to the user, so the memory
ownership issues with kernel/user space are interesting. It also has to
somewhat atomically prepare the list and undset the notifier byte, which is
also problematic. But probably workable.
It sounds like we will have another 5k lines of code in MPI that will
try to resolve
the kernel/user notification issue :-)
IMHO, Lets avoid all these tricks and move the registration cache to kernel.
Pasha
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