weird memshared value

weird memshared value

[Roberto Orenstein]

Hi Cristoph,

Guess found a bug in the MemShared value that shows up in /proc/meminfo.
At least it's pretty weird :)

After a cp kernel_tree new_tree, together with make bzImage, got the 
following number:

MemShared:    4294966488 kB

My system has only 128MB. P-III, kernel 2.4.9-ac16.
It doesn't harm, but it's way far from my system mem.

Any idea?

thanx

Roberto

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Re: weird memshared value

[Mike Fedyk]

On Wed, Oct 03, 2001 at 06:13:03PM -0300, Roberto Orenstein wrote:
> Hi Cristoph,
> 
> Guess found a bug in the MemShared value that shows up in /proc/meminfo.
> At least it's pretty weird :)
> 
> After a cp kernel_tree new_tree, together with make bzImage, got the 
> following number:
> 
> MemShared:    4294966488 kB
> 
> My system has only 128MB. P-III, kernel 2.4.9-ac16.
> It doesn't harm, but it's way far from my system mem.
> 

I've just come across this myself.  There is a patch on lkml, look for the
thread ~"4gb memshared, cached bigger than memtotal"...

Mike
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Re: weird memshared value

[Mike Fedyk]

On Wed, Oct 03, 2001 at 06:13:03PM -0300, Roberto Orenstein wrote:
> Hi Cristoph,
> 
> Guess found a bug in the MemShared value that shows up in /proc/meminfo.
> At least it's pretty weird :)
> 
> After a cp kernel_tree new_tree, together with make bzImage, got the 
> following number:
> 
> MemShared:    4294966488 kB
> 
> My system has only 128MB. P-III, kernel 2.4.9-ac16.
> It doesn't harm, but it's way far from my system mem.
> 
> Any idea?
> 

Here you go:

Date: Mon, 1 Oct 2001 22:17:26 +0100 (BST)
From: Hugh Dickins <hugh@veritas.com>
X-Sender: hugh@localhost.localdomain
To: Christoph Rohland <cr@sap.com>
cc: Mike Fedyk <mfedyk@matchmail.com>, Alan Cox <alan@lxorguk.ukuu.org.uk>,
   linux-kernel@vger.kernel.org
Subject: [PATCH] Re: 4GB MemShared, Cached bigger (and growing) than MemTotal
 (64MB) on 2.4.9-ac18
In-Reply-To: <m34rpj3lsa.fsf@linux.local>
Message-ID: <Pine.LNX.4.21.0110012142400.1098-100000@localhost.localdomain>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Status: RO
Content-Length: 778
Lines: 25

On 1 Oct 2001, Christoph Rohland wrote:
> On Sun, 30 Sep 2001, Mike Fedyk wrote:
> > 
> > After this happened, I saw MemShared go up to about 4GB, and Cached
> > started growing, getting even bigger than ram!
> 
> Apparently the shmem accounting is screwed. (Hugh does something ring
> at your side?) 

I've now looked, and it's obviously my error in -ac shmem_writepage:
patch below against 2.4.10-ac2, would apply equally to 2.4.9-ac16 on.

Hugh

--- 2.4.10-ac2/mm/shmem.c	Mon Oct  1 21:36:28 2001
+++ linux/mm/shmem.c	Mon Oct  1 21:41:00 2001
@@ -462,6 +462,7 @@
 		swap_list_unlock();
 		/* Add it back to the page cache */
 		add_to_page_cache_locked(page, mapping, index);
+		atomic_inc(&shmem_nrpages);
 		activate_page(page);
 		SetPageDirty(page);
 		error = -ENOMEM;


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Re: weird memshared value

[Mike Fedyk]

On Wed, Oct 03, 2001 at 07:33:01PM -0300, Roberto Orenstein wrote:
> Hi Mike
> 
> Thanx for the help. Patch applied and problem vanish :)
> 
> 
> regards
> 
> Roberto
> 

Be sure to post that to the list.  We need success reports for these types
of things.

I have yet to test the patch myself.

I was able to reliably reproduce it by setting my ram down to 64mb with no
swap and running mozilla with kde...

Mike
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Re: weird memshared value

[Roberto Orenstein]

now I remebered to post to the list. guess I need to take a rest :(

 Mike Fedyk wrote:
 
> On Wed, Oct 03, 2001 at 07:33:01PM -0300, Roberto Orenstein wrote:
> 
>> Hi Mike
>> 
>> Thanx for the help. Patch applied and problem vanish :)
>> 
>> 
>> regards
>> 
>> Roberto
>> 
> 
 
> Be sure to post that to the list.  We need success reports for these 
> types
> of things.
 
     
 Ok. I just thought it was a well know thing that I missed :)
 
> I have yet to test the patch myself.
> 
> I was able to reliably reproduce it by setting my ram down to 64mb 
> with no
> swap and running mozilla with kde...
 
 
 I run that test and it didn't trigger.
 I also did the same thing that trigger it here: cp kernel_source 
 new_source and a make bzImage in another term. Everythig is normal. Just 
 fine.
 
 Roberto


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