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

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Message-ID: <4B7ACD4A.10101@nortel.com>
Date:	Tue, 16 Feb 2010 10:52:26 -0600
From:	"Chris Friesen" <cfriesen@...tel.com>
To:	Rik van Riel <riel@...hat.com>
CC:	Minchan Kim <minchan.kim@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.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 02/15/2010 11:00 AM, Rik van Riel wrote:
> On 02/15/2010 10:50 AM, Chris Friesen wrote:
> 
>> Looking at the code, it looks like page_remove_rmap() clears the
>> Anonpage flag and removes it from NR_ANON_PAGES, and the caller is
>> responsible for removing it from the LRU.  Is that right?
> 
> Nope.
> 
>> I'll keep digging in the code, but does anyone know where the removal
>> from the LRU is supposed to happen in the above code paths?
> 
> Removal from the LRU is done from the page freeing code, on
> the final free of the page.
> 
> It appears you have code somewhere that increments the reference
> count on user pages and then forgets to lower it afterwards.

Okay, that makes sense.

I'm still trying to get a handle on the LRU removal though.  The code
path that I saw most which resulted in clearing the anon bit but leaving
the page on the LRU was the following:


    [<ffffffff8029c951>] kmemleak_clear_anon+0x7f/0xbe
    [<ffffffff802864c7>] page_remove_rmap+0x45/0x146
    [<ffffffff8027dc7e>] unmap_vmas+0x41c/0x948
    [<ffffffff80282405>] exit_mmap+0x7b/0x108
    [<ffffffff8022f441>] mmput+0x33/0x110
    [<ffffffff80233b05>] exit_mm+0x103/0x130
    [<ffffffff802355b5>] do_exit+0x17b/0x91f
    [<ffffffff80235d95>] do_group_exit+0x3c/0x9c
    [<ffffffff80235e07>] sys_exit+0x0/0x12
    [<ffffffff8021ddb5>] ia32_syscall_done+0x0/0xa

There are a bunch of inline functions involved, but I think the chain
from page_remove_rmap() back up to unmap_vmas() looks like this:

page_remove_rmap
zap_pte_range
zap_pmd_range
zap_pud_range
unmap_page_range
unmap_vmas

So in this scenario, where do the pages actually get removed from the
LRU list (assuming that they're not in use by anyone else)?

Thanks,

Chris
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