Re: [Bug #14141] order 2 page allocation failures in iwlagn

[Mel Gorman]

On Thu, Oct 15, 2009 at 10:15:09PM +0200, Frans Pop wrote:
> On Thursday 15 October 2009, Mel Gorman wrote:
> > After a lot more eyeballing, the best next candidate within mm is the
> > following patch. Should be tested on it's own and in combination with
> > the wakeup-kswapd patch sent before.
> >
> > From 4e8b5217f51a00caee527e4e8d8e46fe9f82b482 Mon Sep 17 00:00:00 2001
> > From: Mel Gorman <mel@xxxxxxxxx>
> > Date: Thu, 15 Oct 2009 00:17:05 +0100
> > Subject: [PATCH] page allocator: Direct reclaim should always obey
> > watermarks
> >
> > ALLOC_NO_WATERMARKS should be cleared when trying to allocate from the
> > free-lists after a direct reclaim.
> 
> I've tested the two patches together and this seems like a definite
> improvement.

You probably don't need the mental image, but this made me do a happy
dance. Certainly helps my cold!

> I still get SKB errors on the first test, but the desktop
> freezes are a lot shorter and the total time needed to load the 3rd gitk
> goes down from ~2:15 to ~1:15. The counter in gitk of the number of
> loaded commits goes up visibly faster and with fewer halts.
> 

This brings us close to the state of affairs before the akpm merge.
There might still be something missing in either the mm area or the wireless
driver but any improvement is better than none.

> This is on top of current mainline with the RX_LOW_WATERMARK in iwlagn
> at it's current value (8).
> 
> Here are the allocation failures for 2 consecutive tests. Note that the
> first test still shows quite a lot of failures, but the second test hardly
> had any at all (I still had music skips though).
> 

So, we are still dealing with three problems.

1. GFP_ATOMICS were introduced to the wireless driver in the
   2.6.30..2.6.31 timeframe. It has been more or less identified as being
   the tasklet off-loading and the pools being depleted too easily. This
   still needs to be fixed. 

2. There is also some firmware reloading problem of an unknown source

3. There was an mm regression that made GFP_ATOMIC failures much worse.
   This is at least partially due to tasks exiting being able to go below the
   watermarks and kswapd not being woken up when it should be.  This could
   be the source of the allocation failures on resume that have nothing to
   do with the iwlagn wireless driver.

I am going to put together the pair of patches against mainline with a
recommendation they be also applied for 2.6.31.5. I'll keep looking to
see can I spot another possible candidate for GFP_ATOMIC being worse
than it was.

> [  232.845116] iwlagn 0000:10:00.0: Failed to allocate SKB buffer with GFP_ATOMIC. Only 0 free buffers remaining.
> [  232.845116] iwlagn 0000:10:00.0: Failed to allocate SKB buffer with GFP_ATOMIC. Only 0 free buffers remaining.
> [  232.873009] iwlagn 0000:10:00.0: Failed to allocate SKB buffer with GFP_ATOMIC. Only 0 free buffers remaining.
> [  232.884545] iwlagn 0000:10:00.0: Failed to allocate SKB buffer with GFP_ATOMIC. Only 0 free buffers remaining.
> [  240.121577] __ratelimit: 26 callbacks suppressed
> [  240.121634] __ratelimit: 6 callbacks suppressed
> [  240.124006] iwlagn 0000:10:00.0: Failed to allocate SKB buffer with GFP_ATOMIC. Only 6 free buffers remaining.
> [  304.335767] iwlagn 0000:10:00.0: Failed to allocate SKB buffer with GFP_ATOMIC. Only 0 free buffers remaining.
> [  304.335767] iwlagn 0000:10:00.0: Failed to allocate SKB buffer with GFP_ATOMIC. Only 0 free buffers remaining.
> [  304.374729] iwlagn 0000:10:00.0: Failed to allocate SKB buffer with GFP_ATOMIC. Only 0 free buffers remaining.
> [  309.446481] __ratelimit: 5 callbacks suppressed
> [  309.450197] iwlagn 0000:10:00.0: Failed to allocate SKB buffer with GFP_ATOMIC. Only 0 free buffers remaining.
> 
> [  525.912934] iwlagn 0000:10:00.0: Failed to allocate SKB buffer with GFP_ATOMIC. Only 5 free buffers remaining.
> [  525.953939] iwlagn 0000:10:00.0: Failed to allocate SKB buffer with GFP_ATOMIC. Only 7 free buffers remaining.
> [  536.058171] __ratelimit: 1 callbacks suppressed
> 

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