linux-kernel - Re: [RFC 2/2] initramfs with digital signature protection

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Date:	Fri, 8 Feb 2013 11:16:23 +0200
From:	"Kasatkin, Dmitry" <dmitry.kasatkin@...el.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Peter Jones <pjones@...hat.com>,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 2/2] initramfs with digital signature protection

On Wed, Feb 6, 2013 at 6:41 PM, H. Peter Anvin <hpa@...or.com> wrote:
> The cleanup is not a umount, it is actually a tree walk unlinking the contents.
>

Please see that umounting ramfs releases the memory.
There was no forced cleanup.
"cp" copied about 2GB of content.
After umounting we got 2GB back to free RAM...

kds@kds:~$ sudo mount -t ramfs testramfs /test
kds@kds:~$ sudo cp -r /usr/ /test
kds@kds:~$ du -sm /test
2154    /test
kds@kds:~$ free
                       total       used            free     shared
buffers     cached
Mem:       8058600    7855780     202820          0      24768    4819136
-/+ buffers/cache:    3011876    5046724
Swap:            0          0          0
kds@kds:~$ sudo umount /test
kds@kds:~$ free
                      total       used            free     shared
buffers     cached
Mem:       8058600    5644864    2413736          0      25268    2623956
-/+ buffers/cache:    2995640    5062960
Swap:            0          0          0

The same happens also with tmpfs.

- Dmitry

> "Kasatkin, Dmitry" <dmitry.kasatkin@...el.com> wrote:
>
>>On Wed, Feb 6, 2013 at 7:04 AM, H. Peter Anvin <hpa@...or.com> wrote:
>>> On 02/05/2013 02:09 PM, Kasatkin, Dmitry wrote:
>>>>
>>>>
>>>> It should not be like that. Actually when pre-init exits, cleanup
>>code
>>>> umount tmpfs, which in turn cleanups the RAM.
>>>>
>>>
>>> It doesn't quite... the rootfs is permanent.  This is also only one
>>usage
>>> mode: there are quite a few Linux systems running directly out of
>>initramfs.
>>>
>>
>>rootfs is not permanent when it is ramfs. It is cleaned up on switch
>>root.
>>It is easy to find out that it is empty by mounting : mount -t ramfs
>>rootfs /mnt/
>>
>>In the case of running from normal storage, of course, there is
>>ridicules remove the content.
>>
>>- Dmitry
>>
>>
>>>         -hpa
>>>
>>>
>>> --
>>> H. Peter Anvin, Intel Open Source Technology Center
>>> I work for Intel.  I don't speak on their behalf.
>>>
>
> --
> Sent from my mobile phone. Please excuse brevity and lack of formatting.
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