linux-kernel - Re: tracking memory usage/leak in "inactive" field in /proc/meminfo?

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Date:	Thu, 11 Feb 2010 12:54:05 -0600
From:	"Chris Friesen" <cfriesen@...tel.com>
To:	Minchan Kim <minchan.kim@...il.com>
CC:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, Balbir Singh <balbir@...ux.vnet.ibm.com>
Subject: Re: tracking memory usage/leak in "inactive" field in /proc/meminfo?

On 02/10/2010 06:45 PM, Minchan Kim wrote:
> On Thu, Feb 11, 2010 at 2:05 AM, Chris Friesen <cfriesen@...tel.com> wrote:

>> In those spreadsheets I notice that
>> memfree+active+inactive+slab+pagetables is basically a constant.
>> However, if I don't use active+inactive then I can't make the numbers
>> add up.  And the difference between active+inactive and
>> buffers+cached+anonpages+dirty+mapped+pagetables+vmallocused grows
>> almost monotonically.
> 
> Such comparison is not right. That's because code pages of program account
> with cached and mapped but they account just one in lru list(active +
> inactive).
> Also, if you use mmap on any file, above is applied.

That just makes the comparison even worse...it means that there is more
memory in active/inactive that isn't accounted for in any other category
in /proc/meminfo.

> I can't find any clue with your attachment.
> You said you used kernel with some modification and non-vanilla drivers.
> So I suspect that. Maybe kernel memory leak?

Possibly.  Or it could be a use case issue, I know there have been
memory leaks fixed since 2.6.27. :)

> Now kernel don't account kernel memory allocations except SLAB.

I don't think that's entirely accurate.  I think cached, buffers,
pagetables, vmallocUsed are all kernel allocations.  Granted, they're
generally on behalf of userspace.

I've discovered that the generic page allocator (alloc_page, etc.) is
not tracked at all in /proc/meminfo.  I seem to see the memory increase
in the page cache (that is, active/inactive), so that would seem to rule
out most direct allocations.

> I think this patch can help you find the kernel memory leak.
> (It isn't merged with mainline by somewhy but it is useful to you :)
> 
> http://marc.info/?l=linux-mm&m=123782029809850&w=2

I have a modified version of that which I picked up as part of the
kmemleak backport.  However, it doesn't help unless I can narrow down
*which* pages I should care about.

I tried using kmemleak directly, but it didn't find anything.  I've also
tried checking for inactive pages which haven't been written to in 10
minutes, and haven't had much luck there either.  But active/inactive
keeps growing, and I don't know why.

Chris
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