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

Andrew Morton
2006-02-20T07:57:52Z

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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.