Re: -mm merge plans -- lumpy reclaim

[Andrew Morton]

On Wed, 11 Jul 2007 10:34:31 +0100 Andy Whitcroft <apw@xxxxxxxxxxxx> wrote:

> [Seems a PEBKAC occured on the subject line, resending lest it become a
> victim of "oh thats spam".]
> 
> Andy Whitcroft wrote:
> > Andrew Morton wrote:
> > 
> > [...]
> >> lumpy-reclaim-v4.patch
> >> have-kswapd-keep-a-minimum-order-free-other-than-order-0.patch
> >> only-check-absolute-watermarks-for-alloc_high-and-alloc_harder-allocations.patch
> >>
> >>  Lumpy reclaim.  In a similar situation to Mel's patches.  Stuck due to
> >>  general lack or interest and effort.
> > 
> > The lumpy reclaim patches originally came out of work to support Mel's
> > anti-fragmentation work.  As such I think they have become somewhat
> > attached to those patches.  Whilst lumpy is most effective where
> > placement controls are in place as offered by Mel's work, we see benefit
> > from reduction in the "blunderbuss" effect when we reclaim at higher
> > orders.  While placement control is pretty much required for the very
> > highest orders such as huge page size, lower order allocations are
> > benefited in terms of lower collateral damage.
> > 
> > There are now a few areas other than huge page allocations which can
> > benefit.  Stacks are still order 1.  Jumbo frames want higher order
> > contiguous pages for there incoming hardware buffers.  SLUB is showing
> > performance benefits from moving to a higher allocation order.  All of
> > these should benefit from more aggressive targeted reclaim, indeed I
> > have been surprised just how often my test workloads trigger lumpy at
> > order 1 to get new stacks.
> > 
> > Truly representative work loads are hard to generate for some of these.
> >  Though we have heard some encouraging noises from those who can
> > reproduce these problems.

I'd expect that the main application for lumpy-reclaim is in keeping a pool
of order-2 (say) pages in reserve for GFP_ATOMIC allocators.  ie: jumbo
frames.

At present this relies upon the wakeup_kswapd(..., order) mechanism.

How effective is this at solving the jumbo frame problem?

(And do we still have a jumbo frame problem?  Reports seems to have subsided)
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