From owner-linux-mm-www@nl.linux.org Thu Dec  2 10:36:49 1999
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Date:   Thu, 02 Dec 1999 10:34:48 +0100
From:   Peter Wurbs <wurbs@bbcom-hh.de>
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Subject: Limitation of buffer allocation
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Hi all,

we deal with an streaming application, whereby some streams of data are
received via a high speed network interface card and  written to the
hard disk. Alle data are only written once and later processed.
By means of "vmstat 1" we found out, that all available free memory is
allocated for buffer cache. Allocation starts, when first data are
received and written to the disk. Allocation ends until about 1 MB is
left free.
This kind of allocation is a big problem for the driver of the network
interface card. It allocates memory dynamically by means of "alloc_skb".
If there is a ad-hoc requierement of a bigger memory block, this
function seems to be unable to take away memory from the buffer cache.
Thus alloc_skb returns null pointer, because it must be invoked with
flag "GFP_ATOMIC" (sudden return if there is no memory available). As a
result the driver runs into a faulty deadlocked state.
We work with kernel 2.2.13.
Furthermore we found out that the limitation of memory allocation for
the buffer cache solves the problem. If there is about 2 MB memory left
free for the driver, it never runs into the problem.
We tested some ways to limit buffer allocation:
1)
A tiny user program allocates permanent memory and frees it immediately.
The user program takes the memory from the buffers. Thus it is available
for the driver.
It is straightforward with unknown side effects, but it works.
2)
We changed the values in /proc/sys/vm/freepages.
The min value is the memory space, reserved for the kernel and thus for
the driver. This space can't allocated for buffers.
Increasing the values reserves more space for the kernel. It works too,
and seems to be a fine solution.
3)
We tried to change the values in /proc/sys/vm/buffermem. (Values are
described in /usr/src/linux/Documentation/proc.txt )
But these values dont have any influence on the buffer allocation. Why?

Any comments?

Do you see problems in changing the values in /proc/sys/vm/freepages?
Is there any other solution?

Thanks in advance and bye,


Peter.

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From owner-linux-mm-www@nl.linux.org Fri Dec 10 21:31:04 1999
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From:   "tinahamer" <tinahamer@ukonline.co.uk>
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Date:   Fri, 10 Dec 1999 20:31:10 -0000
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hello just wondered whether you could help me I have t investigate the =
implementation of memory management in Linux or Unix for an assignment.  =
Do you know of any good websites or books etc that could help me in my =
research

Thankyou=20
Tina

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<DIV><FONT color=3D#000000 size=3D2>hello just wondered whether you =
could help me I=20
have t investigate the implementation of memory management in Linux or =
Unix for=20
an assignment.&nbsp; Do you know of any good websites or books etc that =
could=20
help me in my research</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT color=3D#000000 size=3D2>Thankyou </FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>Tina</FONT></DIV></BODY></HTML>

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From owner-linux-mm-www@nl.linux.org Sun Dec 12 13:48:37 1999
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From:   marcel@nl.linux.org (Marcel Harkema)
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Op vrijdag 10 december 1999 rond 20:31 -0000 schreef tinahamer:

> hello just wondered whether you could help me I have t investigate the
> implementation of memory management in Linux or Unix for an assignment.=
=20
> Do you know of any good websites or books etc that could help me in my
> research
>=20
> Thankyou=20
> Tina

  Check out the UVM link on the Linux-MM www links page.  UVM is currently
  used in NetBSD and OpenBSD.  The UVM paper is an excellent read, it also
  refers to other VM papers and VM subsystems of other operating systems.

  You may want to read a book like Modern Operating Systems by Andy
  Tanenbaum too.

  I am working on a MM reference page, including lots of papers.  But that
  won't be finished until late January 2000, since I am currently working on
  my msc. thesis (this is my last month).

  There are more good MM links on Linux-MM, for instance the VM tutorial.

  See http://www.linux.eu.org/Linux-MM/mm-links.html.

  If you find interesting links, please forward them to us, so we can
  include them on the Linux-MM pages.

  Finally, if you make your report available on the web, please let us know
  too, so we can link that.

  Cheers,

         Marcel

--=20
"Beware of bugs in the above code; I have only proved it correct,
 not tried it." --Donald E. Knuth

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From owner-linux-mm-www@nl.linux.org Tue Dec 21 06:35:30 1999
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Date:   Mon, 20 Dec 1999 21:31:26 -0800 (PST)
From:   =?gb2312?q?do=20do?= <flygong@yahoo.com>
Subject:  Linux kernel question
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Hello croutons:
	I'm a chinese student reading linux
2.0.34 version source code .I meet some question.Mybe
you can help me.My questions :the first,what does the
linux 
memory layout look like?the second question:there a
line
"memory_start = (unsigned long) &_end;"in function of
void setup_arch in linux/arch/i386/kernel/setup.c,what
is 
"_end"? And could you tell me where to find document
aout
these question?
	Thank you !
			you honest friend  gong 99/12/22

	My e_mail:flygong@yahoo.com



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From owner-linux-mm-www@nl.linux.org Tue Dec 21 06:41:00 1999
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Date:   Mon, 20 Dec 1999 21:37:00 -0800 (PST)
From:   =?gb2312?q?do=20do?= <flygong@yahoo.com>
Subject:  Linux kernel question
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Hello croutons:
	I'm a chinese student reading linux
2.0.34 version source code .I meet some question.Mybe
you can help me.My questions :the first,what does the
linux 
memory layout look like?the second question:there a
line
"memory_start = (unsigned long) &_end;"in function of
void setup_arch in linux/arch/i386/kernel/setup.c,what
is 
"_end"? And could you tell me where to find document
aout
these question?
	Thank you !
			you honest friend  gong 99/12/22

	My e_mail:flygong@yahoo.com



__________________________________________________
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Thousands of Stores.  Millions of Products.  All in one place.
Yahoo! Shopping: http://shopping.yahoo.com
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