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

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Date:	Fri, 20 Apr 2007 21:14:43 +0800
From:	"Aubrey Li" <aubreylee@...il.com>
To:	"David Howells" <dhowells@...hat.com>
Cc:	"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 4/20/07, David Howells <dhowells@...hat.com> wrote:
> Aubrey Li <aubreylee@...il.com> wrote:
>
> > as checked in packet_set_ring, buffer size must be a multiple of PAGE_SIZE,
> > --------------------packet_set_ring------------------------
> > if (unlikely(req->tp_block_size & (PAGE_SIZE - 1)))
> >
> > So why not use __get_free_pages rather than kmalloc,
>
> 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.
>

>> so that we have pagetables to count?

>There are no pagetables in NOMMU-mode.

Hmm..., I'm thinking some codes in memory reclaim depend on
NR_FILE_MMAPED like follows
----snip----
if (zone_page_state(zone, NR_FILE_PAGES) -
                        zone_page_state(zone, NR_FILE_MAPPED) >
                        zone->min_unmapped_pages)
----snip----
Since we are enabling packet mmap feature, we should take its mapped
pages into count of NR_FILE_MAPPED.

-Aubrey
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