linux-kernel - Re: [RFC] [PATCH] hugetlbfs :shmget with SHM

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Date:	Tue, 29 Jan 2008 20:28:03 +0530
From:	Ciju Rajan K <ciju@...ux.vnet.ibm.com>
To:	William Lee Irwin III <wli@...omorphy.com>
CC:	aglitke <agl@...ibm.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC] [PATCH] hugetlbfs :shmget with SHM_HUGETLB only works as
 root

William Lee Irwin III wrote:
> On Fri, Nov 30, 2007 at 12:02:32AM +0530, Ciju Rajan K wrote:
>>   I tested your patch. But that is not solving the problem.
>>   If the code change to user_shm_lock() is not a good solution, could 
>> you please suggest a method so that the normal user is able to allocate 
>> the huge pages, if his gid is added to /proc/sys/vm/hugetlb_shm_group
> 
> The patch I posted resolves a race unrelated to your issue. Raising your
> locked memory limits should not be difficult. /etc/limits.conf or similar
> should set it up for you. You can also change the default rlimit in the
> kernel and compile it with default limits elevated to what you want your
> unprivileged process to have to start with if you're truly having lots
> of trouble getting userspace to set the default limits properly. I'd
> look in include/asm-generic/resource.h
> 
> 
> -- wli

Hi Wli,

The documentation available in the kernel for huge pages does not talk
about the issue associated with locked memory limit. I think it would be
helpful to the users if we mention about this in the documentation. I
am attaching a small documentation patch.

Thanks
Ciju

Signed-off-by: Ciju Rajan (ciju@...ux.vnet.ibm.com)
---
--- Documentation/vm/hugetlbpage.txt.orig       2008-01-24 16:42:40.000000000 +0530
+++ Documentation/vm/hugetlbpage.txt    2008-01-29 19:36:45.000000000 +0530
@@ -108,6 +108,18 @@ a supplementary group and system admin n
  applications to use any combination of mmaps and shm* calls, though the
  mount of filesystem will be required for using mmap calls.

+Note: The default locked limit in the kernel is just 32KB. If the normal
+user whose gid is present in the file /proc/sys/vm/hugetlb_shm_group needs
+more memory than this, the default limit must be increased. If pam is installed
+on your system, resource limits can be configured by installing lines similar
+to the following in /etc/security/limits.conf:
+
+@...egroup      soft    memlock         2097152
+@...egroup      hard    memlock         2097152
+
+Otherwise, you may manipulate the locked limit command directly with 'ulimit'.
+See its man page for more information.
+
  *******************************************************************

  /*

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