netdev - Re: ppp_deflate + kmalloc

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Date:	Sun, 26 Jun 2011 23:17:54 +0200
From:	Martin Jackson <mjackson220.list@...il.com>
To:	James Carlson <carlsonj@...kingcode.com>
Cc:	paulus@...ba.org, linux-ppp@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: ppp_deflate + kmalloc

On Fri, Jun 24, 2011 at 4:02 PM, James Carlson <carlsonj@...kingcode.com> wrote:
> Martin Jackson wrote:
>> In our android froyo-based system (omap3 hardware), we are getting the
>> following problem where the ppp driver cannot kmalloc enough memory
>> for the decomp buffer in the ppp driver.
>>
>> Trying to make a 4th-order kmalloc (I think that amounts to 64kB)
>> seems ambitious. I do not understand why vmalloc is not being used
>> here, like it is for the compression buffer. Is using vmalloc here an
>> acceptable solution?
>
> The code here shouldn't need contiguous pages, so vmalloc (even if
> "slower") shouldn't be a problem.
>
> But a higher-level question might be why you're bothering with RFC 1979
> Deflate compression at all on this platform.  I'd expect that you're
> most likely going to end up talking to commercially-produced PPP servers
> (possibly 3GPP or similar) at the other end, and very, very few of them
> offer data compression with either RFC 1977 (BSD Compression) or RFC
> 1979.  ("Very, very few" is probably being generous ...)
>
> If it's always going to be negotiated away in practice, and if you're
> having trouble with memory constraints, why not just ditch the baggage?
>
> --
> James Carlson         42.703N 71.076W         <carlsonj@...kingcode.com>
>

Thanks for the advice. Hopefully we can indeed remove these obscure
PPP options from our configuration - I'll look into that.

However, the point still stands that a 4th order kmalloc is likely to
fail (even our "embedded" device has 256MB RAM and slub allocator,
after all), and the page allocation code regards anything above order
3 as unrealistic and doesn't invoke the OOM to try to satisfy it, so
my view remains that this should be changed to vmalloc.

Best regards,

Martin Jackson
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