Re: [Xen-devel] 0-order allocation failed

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

This means that a number of GFP_ATOMIC allocations failed. This is no
surprise in a low-memory location where your root filesystem is
mounted over NFS: Linux isn't able to launder and evict pages quickly
enough to satisfy all non-blocking page-allocation requests.

I can practically guarantee exactly the same behaviour in native Linux
under the same circumstances (we saw various NFS-root weirdnesses on
native Linux under high load when stress-testing the MM code).

 -- Keir


> Looks like yesterday's paging problems were an artifact of something on
> that particular dom0 disk image -- I haven't been able to reproduce it
> on other nodes, and after I re-imaged the same node (with the same
> image), the problem has gone away there too, so that rules out hardware.  
> 
> However, something else did pop up -- while trying to break things with
> "perl -e '$a="a"x100000000'", I got the following messages; do we care?
> This is in mainstream linux mm/page_alloc.c, and it's hard for me to
> tell from the code whether these are outright errors or whether they
> were recoverable.  Does anyone know?
> 
>   DOM4: __alloc_pages: 0-order allocation failed (gfp=0xf0/0)
>   DOM4: __alloc_pages: 0-order allocation failed (gfp=0xf0/0)
>   DOM4: __alloc_pages: 0-order allocation failed (gfp=0xf0/0)
>   DOM4: __alloc_pages: 0-order allocation failed (gfp=0xf0/0)
> 
> This was still on last Monday's version of 1.2; I'll see if I can
> reproduce it in today's 1.2; I'm deploying that later tonight.
> 
> Steve


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