netdev - Re: [PATCH] CONFIG_PACKET_MMAP should depend on MMU

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Message-Id: <20070420111727.fc69d671.dada1@cosmosbay.com>
Date:	Fri, 20 Apr 2007 11:17:27 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	David Howells <dhowells@...hat.com>
Cc:	"Aubrey Li" <aubreylee@...il.com>,
	"Robin Getz" <rgetz@...ckfin.uclinux.org>, uaca@...mni.uv.es,
	bryan.wu@...log.com, "Alan Cox" <alan@...rguk.ukuu.org.uk>,
	waltje@...lt.nl.mugnet.org, netdev@...r.kernel.org,
	"Andrew Morton" <akpm@...l.org>,
	"Linux Kernel" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] CONFIG_PACKET_MMAP should depend on MMU

On Fri, 20 Apr 2007 09:58:52 +0100
David Howells <dhowells@...hat.com> wrote:
> 
> Because kmalloc() may be able to get us a smaller chunk of memory.  Actually,
> calling __get_free_pages() might be a better, and then release the excess
> pages.

Interesting, that rings a bell here.

I wonder why we dont use this in alloc_large_system_hash().

(if __get_free_pages(GFP_ATOMIC, order) is used instead of alloc_bootmem() or __vmalloc())

We currently loose 1/4 of space on tcp hash table for example, because sizeof(inet_ehash_bucket) is not a power of 2.

Is it really possible to allocate an order-10 page, then release part of it (say an order-8 subpage) ?

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