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From: ebiederm@xmission.com (Eric W. Biederman)
To: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 01/23] tref: Implement task references.
Date: Thu, 02 Mar 2006 15:19:27 -0700	[thread overview]
Message-ID: <m14q2gjxqo.fsf@ebiederm.dsl.xmission.com> (raw)
In-Reply-To: <44074479.15D306EB@tv-sign.ru> (Oleg Nesterov's message of "Thu, 02 Mar 2006 22:16:09 +0300")

Oleg Nesterov <oleg@tv-sign.ru> writes:

> Eric W. Biederman wrote:
>>
>> Holding a reference to a task_struct pins about 10K of low memory even after
>> that task has exited.  Which seems to be at 1 or 2 orders of mangnitude more
>> memory than any other data structure in the kernel.  Not holding a reference
>> to a task_struct and you risk problems with pid wrap around.
>
> I think there is another, much simpler solution. We can make a "reference" to
> the
> pid itself to protect it against free_pidmap(), so that this pid can't be
> reused.

I kind of like the idea of not releasing the pid when someone is using it.
However with my trivial hostile program I can with 32 or 33 living processes
each with 1000 references to dead processes I can completely saturate the
default pid map.  And it won't be obvious why alloc_pidmap is failing.

Your resource consumption with the extra hash table is higher than
mine at until very high process counts.

In addition it doesn't really help with the problem that inspired
this work.  That of having multiple pid spaces.  I could make it work
by throwing a pspace reference in struct pid_ref, but without some
fancy footwork it would prevent cleanup until all of the outside
references are gone.

> What do you think?

So I kind of like it but I don't feel it does as good a job solving
the problems I am solving.  

In this instance I'm not at all certain I like having NULL ref
pointers.  It increases the number of cases you have to deal with when
reading back the pid, but that is minor and something task_refs suffer
from more than pid_refs.

Eric

  parent reply	other threads:[~2006-03-02 22:21 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2006-02-23 15:52 [PATCH 00/23] proc cleanup Eric W. Biederman
2006-02-23 15:54 ` [PATCH 01/23] tref: Implement task references Eric W. Biederman
2006-02-23 15:56   ` [PATCH 02/23] proc: Fix the .. inode number on /proc/<pid>/fd Eric W. Biederman
2006-02-23 15:57     ` [PATCH 03/23] proc: Remove useless BKL in proc_pid_readlink Eric W. Biederman
2006-02-23 15:58       ` [PATCH 04/23] proc: Remove unnecessary and misleading assignments from proc_pid_make_inode Eric W. Biederman
2006-02-23 16:00         ` [PATCH 05/23] proc: Simplify the ownership rules for /proc Eric W. Biederman
2006-02-23 16:02           ` Eric W. Biederman
2006-02-23 16:04           ` [PATCH 06/23] proc: Replace proc_inode.type with proc_inode.fd Eric W. Biederman
2006-02-23 16:05             ` [PATCH 07/23] proc: Remove bogus proc_task_permission Eric W. Biederman
2006-02-23 16:06               ` [PATCH 08/23] proc: Kill proc_mem_inode_operations Eric W. Biederman
2006-02-23 16:08                 ` [PATCH 09/23] proc: Properly filter out files that are not visible to a process Eric W. Biederman
2006-02-23 16:10                   ` [PATCH 10/23] proc: Fix the link count for /proc/<pid>/task Eric W. Biederman
2006-02-23 16:12                     ` [PATCH 11/23] proc: Move proc_maps_operations into task_mmu.c Eric W. Biederman
2006-02-23 16:15                       ` [PATCH 12/23] proc: Rewrite the proc dentry flush on exit optimization Eric W. Biederman
2006-02-23 16:16                         ` [PATCH 13/23] proc: Close the race of a process dying durning lookup Eric W. Biederman
2006-02-23 16:18                           ` [PATCH 14/23] proc: Make PROC_NUMBUF the buffer size for holding a integers as strings Eric W. Biederman
2006-02-23 16:20                             ` [PATCH 15/23] proc: refactor reading directories of tasks Eric W. Biederman
2006-02-23 16:23                               ` [PATCH 16/23] proc: Don't lock task_structs indefinitely Eric W. Biederman
2006-02-23 16:24                                 ` [PATCH 17/23] proc: Give the root directory a task Eric W. Biederman
2006-02-23 16:25                                   ` [PATCH 18/23] proc: Reorder the functions in base.c Eric W. Biederman
2006-02-23 16:27                                     ` [PATCH 19/23] proc: Modify proc_pident_lookup to be completely table driven Eric W. Biederman
2006-02-23 16:28                                       ` [PATCH 20/23] proc: Make the generation of the self symlink " Eric W. Biederman
2006-02-23 16:30                                         ` [PATCH 21/23] proc: Factor out an instantiate method from every lookup method Eric W. Biederman
2006-02-23 16:32                                           ` [PATCH 22/23] proc: Remove the hard coded inode numbers Eric W. Biederman
2006-02-23 16:34                                             ` [PATCH 23/23] proc: Merge proc_tid_attr and proc_tgid_attr Eric W. Biederman
2006-02-23 16:49   ` [PATCH 01/23] tref: Implement task references Eric W. Biederman
2006-03-02 19:16     ` Oleg Nesterov
2006-03-02 20:37       ` Oleg Nesterov
2006-03-02 22:19       ` Eric W. Biederman [this message]
2006-03-03 16:56         ` Oleg Nesterov
2006-03-03 17:48           ` Eric W. Biederman
2006-03-04 11:16           ` Eric W. Biederman
2006-03-04 12:31             ` Oleg Nesterov
2006-03-04 17:30               ` Oleg Nesterov
2006-03-06 21:06         ` Oleg Nesterov
2006-03-06 22:18           ` Eric W. Biederman
2006-03-07 20:44             ` Oleg Nesterov
2006-03-07  1:39           ` Eric W. Biederman
2006-03-07 20:38             ` Oleg Nesterov
2006-03-07 13:12           ` Eric W. Biederman
2006-03-07 21:02             ` Oleg Nesterov
2006-03-07 23:00               ` Eric W. Biederman
2006-03-03 19:23     ` Oleg Nesterov
2006-03-04 10:51       ` Eric W. Biederman
2006-02-25 12:27 ` [PATCH 00/23] proc cleanup Andrew Morton
2006-02-25 13:34   ` Eric W. Biederman
2006-02-25 15:20   ` Eric W. Biederman
2006-02-27 15:26 ` Serge E. Hallyn
2006-02-27 15:56   ` Eric W. Biederman

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