netdev - Re: [PATCH 1/2] r8169: allocate with GFP

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Date:	Fri, 08 Oct 2010 17:04:07 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Stanislaw Gruszka <sgruszka@...hat.com>
Cc:	Francois Romieu <romieu@...zoreil.com>, netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] r8169: allocate with GFP_KERNEL flag when able to
 sleep

Le vendredi 08 octobre 2010 à 16:52 +0200, Stanislaw Gruszka a écrit :
> On Fri, Oct 08, 2010 at 04:25:00PM +0200, Stanislaw Gruszka wrote:
> > We have fedora bug report where driver fail to initialize after
> > suspend/resume because of memory allocation errors:
> > https://bugzilla.redhat.com/show_bug.cgi?id=629158
> 
> There is also one more thing to do regarding above. Calltraces from bug
> reports, shows that order 3 allocation fail. On arch with 4kB pages,
> order 3 mean 32kB allocation. We want to alloc 16kB, but there is also
> internal sk_buff data what make that we exceed the boundary and take
> 32kB from allocator, getting almost 50% wastage.
> 

Or its only an 1460+overhead allocation, and SLUB uses order-3 pages to
satisfy 2048 bytes allocations.

# grep 2048 /proc/slabinfo 
kmalloc-2048        8664   8752   2048   16    8 : tunables    0    0
0 : slabdata    547    547      0


8 in the <pagesperslab> column just says that : order-3 pages, even for
small allocations.

Switch to SLAB -> no more problem ;)


> To fix we can use similar method as in niu or iwlwifi drivers, alloc
> pages directly form buddy allocator and attach them to skb (by
> skb_add_rx_frag for example). I'm going to prepare such patch, but
> I have one doubt, what happens if page size in system is bigger
> than 16kB, should I care about such case? 

Seems tricky. Should we patch all drivers to do something like that ?



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