Re: Flames over -- Re: Which is simpler?

[Andrew Morton <akpm@osdl.org>]

Andrew Morton <akpm@osdl.org> 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.