Hello,
I would like to have a discussion about current state of kernel AIO - an
interface that lets kernel callers submit aio iocbs without going
through the user space syscalls. The patches implementing the feature
were developed and sent to mailing lists many times by Zach Brown and
Dave Kleikamp long while ago. Then, after LSF/MM 2014, Alexander Viro
made significant progress wiring ITER_BVEC into VFS call paths. His
efforts made adding support of kernel AIO much easier as was recently
demonstrated by Ming Lei's patches converting loop driver to blk-mq, but
for some reasons the feature is still out of tree. An interesting aspect
of the problem to be discussed is blocking/nonblocking behavior of
aio_kernel_submit: even if it blocks only in rare cases, the caller
(e.g. loop driver) must always use a separate thread for processing -
extra overhead that can be avoided.
Thanks,
Maxim
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