Re: [Bug #13319] Page allocation failures with b43 and p54usb

Mel Gorman
2009-06-08T13:35:20Z

On Mon, Jun 08, 2009 at 09:20:23AM -0400, Rik van Riel wrote:
> Mel Gorman wrote:
>
>> We've encountered this before and the conclusion was that the current
>> adjustments for watermark calculations of high-order allocations is right,
>> or at least there is no better alternative. In other words, the page
>> allocator in this instance is behaving as expected. Do we want to
>> revisit that discussion as to whether the watermark calculations for
>> high-order allocation should change? I think we'll reach the same
>> conclusion or at least decide that allowing the order-1 atomic
>> allocation to succeed here would just postpone the problem.
>
> It would not just postpone the problem, it would also
> bring the system closer to a state where kswapd does
> something about the order-1 free areas.
>
> This might postpone the problem indefinately.
>

How do you figure it does not just postpone the problem? If there are a batch
of order-1 allocations that come in like this, it will eventually deplete
the higher-order pages and then fail because kswapd is not getting woken up.

Minimally, if we were to ignore the watermarks, there would need to be logic
that says

"If a high-order allocation would fail due to high-order watermarks
not being met, but the watermarks are ok from an order-0 perspective
and the high-order page is available, then grant the allocation but
wake up kswapd as if the order-1 allocation had failed to get the
high-order watermarks back in shape"

> Currently the system fails early, without kswapd
> kicking in and freeing new order-1 areas.
>

If the allocation was granted, then kswapd will still not kick in.

--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab