[2237] in linux-net channel archive
Re: Optimising for packet sniffing
daemon@ATHENA.MIT.EDU (Alex.Bligh)
Mon Mar 25 12:41:34 1996
To: Nick.Holloway@alfie.demon.co.uk (Nick Holloway)
cc: submit-linux-dev-net@ratatosk.yggdrasil.com
In-reply-to: Your message of "25 Mar 1996 16:55:52 GMT."
<4j6j6o$11f@alfie.demon.co.uk>
Date: Mon, 25 Mar 1996 17:19:12 +0000
From: "Alex.Bligh" <amb@xara.net>
> I've installed Linux 1.3.75 on a 486sx20 laptop with 8Mb of RAM, so I
> can use tcpdump to try and get a handle on a problem we are seeing.
>
> The worrying aspect is that I get "Couldn't get a free page" reasonably
> often. Are there parameters I can tune in /proc/sys to try and help
> with keeping memory available for incoming packets?
Try increasing MAX_SECONDARY_PAGES in memory.h, or (if the problem is
large (i.e. greater than slightly less than page sized) packets which
means you are running with a non-ethernet MTU) edit __get_free_pages()
in mm/swap.c so it rather than cauing non GFP_ATOMIC requests to cause
a virtual-out when the number of pages gets below a given threshold,
check a couple of the free lists to see if they are near empty instead.
Please note that either of these will probably cause more swapping than
normal under normal use (you are effectively dedicating a larger amount
of pages for use by IRQ/bh routines).
Alex Bligh
Xara Networks
