linux-kernel - Re: upcoming kerneloops.org item: get_page_from

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Message-ID: <alpine.LFD.2.01.0906240948430.3240@localhost.localdomain>
Date:	Wed, 24 Jun 2009 09:52:17 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: upcoming kerneloops.org item: get_page_from_freelist

On Wed, 24 Jun 2009, Andrew Morton wrote:
> 
> Well yes.  Using GFP_NOFAIL on a higher-order allocation is bad.

Yes, but your definition of "higher order" is incorrect.

At the very least, we should change the "order > 0" to "order > 1".

As I already mentioned, SLAB uses order-1 allocations in order to not have 
excessive fragmentation for small kmalloc/slab's that would otherwise 
waste tons of memory.

Think network packets at 1500 bytes each. You can allocate two per page, 
or five per 2-pages. That's a 25% memory usage difference! 

And getting an order-1 allocation is simply not that much harder than an 
order-0 one. It starts getting hard once you get to order-3 or more.

			Linus
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