[ltt-dev] [PATCH] mm fix page writeback accounting to fix oom condition under heavy I/O

[Nick Piggin]

On Tuesday 10 February 2009 16:23:56 Linus Torvalds wrote:
> On Mon, 9 Feb 2009, Mathieu Desnoyers wrote:
> > So this patch fixes this behavior by only decrementing the page
> > accounting _after_ the block I/O writepage has been done.
>
> This makes no sense, really.
>
> Or rather, I don't mind the notion of updating the counters only after IO
> per se, and _that_ part of it probably makes sense. But why is it that you
> only then fix up two of the call-sites. There's a lot more call-sites than
> that for this function.

Well if you do that, then I'd think you also have to change some
calculations that today use dirty+writeback.

In some ways it does make sense, but OTOH it is natural in the
pagecache since it was introduced to treat writeback as basically
equivalent to dirty. So writeback && !dirty pages shouldn't cause
things to blow up, or if it does then hopefully it is a simple
bug somewhere.