On Tue, Oct 09, 2012 at 03:32:10PM -0700, Zach Brown wrote:

quoted

If it is measurable I'll take another stab at using memory from
__get_free_pages() for the ringbuffer. That really would be the ideal
solution.

No, then you'll run into high order allocation failures with rings that
don't fit in a single page.

Not if we decouple the ringbuffer size from max_requests.

This would be useful to do anyways because right now, allocating a kiocb
has to take a global refcount and check head and tail in the ringbuffer
just so it can avoid overflowing the ringbuffer.

If we change aio_complete() so that if the ringbuffer is full then the
kiocb just goes on a linked list - we can size the ringbuffer so this
doesn't happen normally and avoid the global synchronization in the fast
path.

quoted

The other reason I wanted to do this was for the aio attributes stuff -
for return values, I think the only sane way is for the return values to
go in the ringbuffer, which means records are no longer fixed size so
dealing with pages is even more of a pain.

Then let's see that, please.

I was starting on that, but then I got sidetracked with refactoring...
:P

And can we please stop calling them attributes?  They're inputs and
outputs that change behaviour -- they're interfaces.

Attributes isn't a good name but neither is interfaces, because they
don't exist on their own; they're always attached to some other
interface.

I dunno.

And no, just for the record, I don't think generic packed variable size
structs are worth the trouble.

If we're going to do a generic interface extension mechanism then we
should put it in its own well thought out system calls, not staple it on
to the side of aio because it's there.  It's a really crummy base to
work from.

Not arguing with you about aio, but most of the use cases I have for it
want aio.

So unless we're going to deprecate the existing aio interfaces and make
something better (I wouldn't complain about that!) I do need to make it
work with aio.

Not that I'm opposed to new syscalls passing attributes to sync versions
of read/write/etc, I just haven't started that yet or really thought
about it.