Re: [patch] mm: skip rebalance of hopeless zones

[Simon Kirby <sim@hostway.ca>]

On Wed, Dec 08, 2010 at 05:23:24PM -0800, Andrew Morton wrote:

> People at google have told me they've seen the same thing.  A fork is
> taking 15 minutes when someone else is doing a dd, because the fork
> enters direct-reclaim trying for an order-one page.  It successfully
> frees some order-one pages but before it gets back to allocate one, dd
> has gone and stolen them, or split them apart.
> 
> This problem would have got worse when slub came along doing its stupid
> unnecessary high-order allocations.

Yeah, we can all blame slub, but even when I force everything to be
order-0 except task_struct and kmalloc(>4096), I still see problems, even
if they aren't as obvious.

Until reclaim holds a page it is about to turn into an order-1, or until
it can hold all of the pages until the watermark is reached including the
allocation it may be directly reclaiming for, this operation is always
going to be non-fair so long as kswapd can run while other allocations
are happening.

Let me guess, Linus will say RCU fixes this.. ;)

Simon-

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