Re: [PATCH 06/13] mm: Preemptible mmu_gather

[Peter Zijlstra <peterz@infradead.org>]

On Fri, 2010-04-09 at 22:36 +0200, Peter Zijlstra wrote:
> On Fri, 2010-04-09 at 13:25 +1000, Nick Piggin wrote:
> > Have you done some profiling on this? What I would like to see, if
> > it's not too much complexity, is to have a small set of pages to
> > handle common size frees, and then use them up first by default
> > before attempting to allocate more.
> > 
> > Also, it would be cool to be able to chain allocations to avoid
> > TLB flushes even on big frees (overridable by arch of course, in
> > case they're doing some non-preeemptible work or you wish to break
> > up lock hold times). But that might be just getting over engineered.

[ patch to do very long queues ]

One thing that comes from having preemptible mmu_gather, and esp. when
we allow such very long gathers, is that we can potentially have a very
large amount of pages stuck on these lists.

So we'd need to hook into reclaim somehow to allow flushing of them when
we're falling short.