From: Avi Kivity <avi@argo.co.il>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: alan@lxorguk.ukuu.org.uk, torvalds@osdl.org, hbryan@us.ibm.com,
akpm@osdl.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, pavel@ucw.cz
Subject: Re: [PATCH] [Request for inclusion] Filesystem in Userspace
Date: Tue, 30 Nov 2004 21:55:40 +0200 [thread overview]
Message-ID: <41ACD03C.9010300@argo.co.il> (raw)
In-Reply-To: <E1CZDUf-0004jM-00@dorka.pomaz.szeredi.hu>
Miklos Szeredi wrote:
>>>And I firmly believe that this can be done without having to special
>>>case filesystem serving processes.
>>>
>>>
>>>
>>>
>>I firmly believe the opposite. When a userspace process calls the kernel
>>which (directly or indirectly) calls the userspace filesystem, the
>>filesystem must have elevated priviledges, or it can deadlock when
>>calling back in.
>>
>>
>
>No.
>
>Just by making the filesystem not contribute to the dirty counters
>(like ramfs), the deadlock problem can be solved. In this case you
>simply could not get a deadlock, because all those dirty pages
>produced by the filesystem look just like normal allocations, which
>simply cannot be touched when the userspace filesystem wants to
>allocate more memory.
>
>In this case the allocation would just fail. Deadlock doesn't happen,
>though the filesystem wasn't given any elevated privileges.
>
>Of course this isn't a good situation: the memory is filled in with
>dirty data of the filesystem which it cannot write back. All sorts of
>
>
you're describing the deadlock here: all memory is full, no process
which allocates memory can make any progress. This is not a true oom
situation: there can be plenty of memory in dirty pagecache which we
could reclaim if we had that tiny bit of reserve memory.
>I looked at ramfs, it isn't even limited. You can easily crash your
>system just by filling it up with data, but no deadlock will happen.
>
>
Right. But ramfs doesn't call a userspace process which calls the kernel
right back.
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
next prev parent reply other threads:[~2004-11-30 20:04 UTC|newest]
Thread overview: 124+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-11-15 21:15 [PATCH] [Request for inclusion] Filesystem in Userspace Miklos Szeredi
2004-11-15 21:43 ` Greg KH
2004-11-15 22:35 ` Linus Torvalds
2004-11-16 9:08 ` Miklos Szeredi
2004-11-16 9:18 ` Arjan van de Ven
2004-11-16 9:40 ` Miklos Szeredi
2004-11-16 9:46 ` Arjan van de Ven
2004-11-16 9:52 ` Miklos Szeredi
2004-11-16 10:17 ` David Woodhouse
2004-11-16 10:25 ` Miklos Szeredi
2004-11-16 10:13 ` Pekka Enberg
2004-11-16 10:20 ` Miklos Szeredi
2004-11-16 10:35 ` Pekka Enberg
2004-11-16 10:42 ` Miklos Szeredi
2004-11-16 12:19 ` Pekka Enberg
2004-11-16 11:01 ` Simon Braunschmidt
2004-11-16 11:20 ` Pekka Enberg
2004-11-16 15:18 ` Ralph Corderoy
2004-11-16 12:31 ` Jan Engelhardt
2004-11-16 11:02 ` Jan Kratochvil
2004-11-16 14:01 ` Miklos Szeredi
2004-11-16 16:33 ` Greg KH
2004-11-16 16:45 ` Miklos Szeredi
2004-11-16 17:03 ` Greg KH
2004-11-16 17:50 ` Miklos Szeredi
2004-11-16 17:58 ` Greg KH
2004-11-16 19:09 ` Miklos Szeredi
2004-11-16 19:16 ` Greg KH
2004-11-16 19:30 ` Miklos Szeredi
2004-11-16 19:38 ` Greg KH
2004-11-16 19:24 ` Jan Engelhardt
2004-11-16 19:32 ` Miklos Szeredi
2004-11-16 19:42 ` Anton Altaparmakov
2004-11-16 19:48 ` Jan Engelhardt
2004-11-16 20:12 ` Miklos Szeredi
2004-11-17 15:42 ` Miklos Szeredi
2004-11-17 16:57 ` Nikita Danilov
2004-11-17 17:10 ` Jan Engelhardt
2004-11-17 17:33 ` Nikita Danilov
2004-11-17 17:38 ` Jan Engelhardt
2004-11-17 17:58 ` Nikita Danilov
2004-11-17 18:09 ` Jan Engelhardt
2004-11-17 19:58 ` Mike Waychison
2004-11-17 18:53 ` [PATCH] " Al Viro
2004-11-17 17:56 ` Miklos Szeredi
2004-11-17 18:11 ` Greg KH
2004-11-17 18:17 ` Miklos Szeredi
2004-11-17 18:20 ` Nikita Danilov
2004-11-17 17:52 ` Greg KH
2004-11-17 15:36 ` Alan Cox
2004-11-17 21:37 ` Bryan Henderson
2004-11-17 19:00 ` Pavel Machek
2004-11-17 19:45 ` Miklos Szeredi
2004-11-17 20:44 ` Pavel Machek
2004-11-18 8:17 ` Miklos Szeredi
2004-11-18 14:46 ` Pavel Machek
2004-11-21 7:42 ` Miklos Szeredi
2004-11-21 7:50 ` Miklos Szeredi
2004-11-21 9:50 ` Jan Hudec
2004-11-21 10:31 ` Miklos Szeredi
2004-11-21 10:39 ` Jan Hudec
2004-11-21 11:29 ` Miklos Szeredi
2004-11-21 11:53 ` Anton Altaparmakov
2004-11-21 12:01 ` Miklos Szeredi
2004-11-21 18:13 ` Pavel Machek
2004-11-22 16:12 ` Miklos Szeredi
2004-11-18 17:00 ` Bryan Henderson
2004-11-18 17:14 ` Miklos Szeredi
2004-11-18 18:49 ` Bryan Henderson
2004-11-18 19:12 ` Miklos Szeredi
2004-11-19 7:01 ` Jan Engelhardt
2004-11-20 12:00 ` Jan Hudec
2004-11-18 17:12 ` Bryan Henderson
2004-11-18 17:28 ` Miklos Szeredi
2004-11-18 18:01 ` Linus Torvalds
2004-11-18 17:29 ` Alan Cox
2004-11-18 18:55 ` Linus Torvalds
2004-11-18 19:28 ` Miklos Szeredi
2004-11-19 9:46 ` Pavel Machek
2004-11-18 20:57 ` Andrew Morton
2004-11-24 6:20 ` Daniel Phillips
2004-11-24 12:15 ` Avi Kivity
2004-11-24 13:05 ` Miklos Szeredi
[not found] ` <200411242001.59504.oliver@neukum.org>
2004-11-24 19:20 ` Miklos Szeredi
2004-11-25 6:26 ` Jan Hudec
2004-11-25 7:29 ` Miklos Szeredi
2004-11-25 7:47 ` Jan Hudec
2004-11-25 9:15 ` Miklos Szeredi
2004-11-25 9:54 ` Pavel Machek
2004-11-30 18:44 ` Avi Kivity
2004-11-30 19:16 ` Miklos Szeredi
2004-11-30 19:55 ` Avi Kivity [this message]
2004-11-30 21:13 ` Miklos Szeredi
2004-11-30 21:37 ` Avi Kivity
2004-11-30 21:58 ` Miklos Szeredi
2004-11-30 22:57 ` Avi Kivity
2004-11-30 23:19 ` Miklos Szeredi
2004-12-15 17:55 ` Avi Kivity
2004-12-15 21:49 ` Miklos Szeredi
2004-12-03 22:07 ` Daniel Phillips
2004-12-15 17:45 ` Avi Kivity
2004-12-01 7:16 ` Jan Hudec
2004-12-01 13:35 ` Miklos Szeredi
2004-11-30 21:54 ` Pavel Machek
2004-11-18 18:21 ` Miklos Szeredi
2004-11-18 18:31 ` Linus Torvalds
2004-11-18 18:56 ` Miklos Szeredi
2004-11-18 19:16 ` Linus Torvalds
2004-11-18 19:33 ` Miklos Szeredi
2004-11-18 19:43 ` Linus Torvalds
2004-11-18 20:05 ` Miklos Szeredi
2004-11-18 20:13 ` Nikita Danilov
2004-11-18 21:06 ` Andrew Morton
2004-11-18 21:33 ` Miklos Szeredi
2004-11-19 11:27 ` Miklos Szeredi
2004-11-27 17:07 ` Rik van Riel
2004-11-27 17:13 ` Pavel Machek
2004-12-03 22:07 ` Daniel Phillips
2004-11-18 20:16 ` Elladan
2004-11-18 18:28 ` Jamie Lokier
2004-11-18 18:47 ` Linus Torvalds
2004-11-18 19:12 ` Bryan Henderson
2004-11-18 19:51 ` Miklos Szeredi
2004-11-18 22:00 ` Jan Hudec
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