Andrew Morton <akpm@xxxxxxxx> wrote: > > > If you simply block writes, the system will stall random tasks laundering > > pages, including those needed to make progress. Even syncing before > > suspend won't help you, as a running user space may dirty pages. > > Well of _course_ that will happen. Actually, it won't happen. There's already logic in there to help pdflush, kswapd and memory-allocating tasks avoid blocking on congested queues. It's trivial to extend that to avoidance of hotunplugged queues. Things like sync(), fsync(), O_SYNC and reads will necessarily block. We may or may not decide to block on page-dirtyings. Again, that's trivial to do in balance_dirty_pages(). Race conditions are pretty much unavoidable - if someone goes and disables a device when we're partway through and committed to I/O submission then things will get very sticky. But we can have a pretty successful solution to all of this without a ton of effort. But this is all the easy part.
