Re: [RFC][PATCH] mm, page_alloc: Warn on !__GFP_NOWARN allocation from IRQ context.

[David Rientjes <rientjes@google.com>]

On Tue, 2 Feb 2016, Tetsuo Handa wrote:

> >From 20b3c1c9ef35547395c3774c6208a867cf0046d4 Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Date: Tue, 2 Feb 2016 16:50:45 +0900
> Subject: [RFC][PATCH] mm, page_alloc: Warn on !__GFP_NOWARN allocation from IRQ context.
> 
> Jan Stancek hit a hard lockup problem due to flood of memory allocation
> failure messages which lasted for 10 seconds with IRQ disabled. Printing
> traces using warn_alloc_failed() is very slow (which can take up to about
> 1 second for each warn_alloc_failed() call). The caller used GFP_NOWARN
> inside a loop. If the caller used __GFP_NOWARN, it would not have lasted
> for 10 seconds.
> 

Sounds like a ratelimiting issue in warn_alloc_failed() with nopage_rs.  
Would it be possible under certain configs to tweak this to not be so 
slow?

Unfortunately, I don't think we can get away with adding a conditional to 
the page allocator hotpath for this, especially if it is only going to 
suggest a kernel patch :)

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