Re: mlock ulimits for SHM_HUGETLB

Re: mlock ulimits for SHM_HUGETLB

[Bharat Agrawal]

Hi all,

Could anyone please help comment on the risks associated with an application throwing the "Using mlock ulimits for SHM_HUGETLB is deprecated" message on RHEL 8.9 with 4.18.0-513.18.1.el8_9.x86_64 Linux kernel?

Best,
Bharat Agrawal
ANSYS, Inc.

Re: mlock ulimits for SHM_HUGETLB

[Greg KH]

On Mon, May 19, 2025 at 10:23:33AM +0000, Bharat Agrawal wrote:
> Hi all,
> 
> Could anyone please help comment on the risks associated with an application throwing the "Using mlock ulimits for SHM_HUGETLB is deprecated" message on RHEL 8.9 with 4.18.0-513.18.1.el8_9.x86_64 Linux kernel?

Why not ask RHEL support, given that you are paying them for that in
order to be using that kernel version, right?

Also note that 4.18.y is VERY old and obsolete and not supported by the
community at all.

Good luck!

greg k-h

Re: mlock ulimits for SHM_HUGETLB

[Bharat Agrawal]

Thanks Greg for the response. RHEL has not been very helpful. I'm not looking to ask for patches because of the old versions.
These messages appear in production runs, raising concerns about possible failures. Thus, the question is: Can they be ignored safely?


Best,
Bharat

________________________________________
From: Greg KH <gregkh@linuxfoundation.org>
Sent: Monday, May 19, 2025 05:02 PM
To: Bharat Agrawal <bharat.agrawal@ansys.com>
Cc: hughd@google.com <hughd@google.com>; akpm@linux-foundation.org <akpm@linux-foundation.org>; rientjes@google.com <rientjes@google.com>; zhangyiru3@huawei.com <zhangyiru3@huawei.com>; liuzixian4@huawei.com <liuzixian4@huawei.com>; mhocko@suse.com <mhocko@suse.com>; wuxu.wu@huawei.com <wuxu.wu@huawei.com>; linux-fsdevel@vger.kernel.org <linux-fsdevel@vger.kernel.org>; linux-kernel@vger.kernel.org <linux-kernel@vger.kernel.org>; linux-api@vger.kernel.org <linux-api@vger.kernel.org>; linux-mm@kvack.org <linux-mm@kvack.org>
Subject: Re: mlock ulimits for SHM_HUGETLB
 
[External Sender]

On Mon, May 19, 2025 at 10:23:33AM +0000, Bharat Agrawal wrote:
> Hi all,
>
> Could anyone please help comment on the risks associated with an application throwing the "Using mlock ulimits for SHM_HUGETLB is deprecated" message on RHEL 8.9 with 4.18.0-513.18.1.el8_9.x86_64 Linux kernel?

Why not ask RHEL support, given that you are paying them for that in
order to be using that kernel version, right?

Also note that 4.18.y is VERY old and obsolete and not supported by the
community at all.

Good luck!

greg k-h

Re: mlock ulimits for SHM_HUGETLB

[Greg KH]

On Mon, May 19, 2025 at 12:04:58PM +0000, Bharat Agrawal wrote:
> Thanks Greg for the response. RHEL has not been very helpful. I'm not looking to ask for patches because of the old versions.
> These messages appear in production runs, raising concerns about possible failures. Thus, the question is: Can they be ignored safely?

Again, you are paying them for support for this, please use them, there
is nothing that the community can do to help out here, sorry.

greg k-h

Re: mlock ulimits for SHM_HUGETLB

[Bharat Agrawal]

No problem. Thanks for your reply.

Bharat
________________________________________
From: Greg KH <gregkh@linuxfoundation.org>
Sent: Monday, May 19, 2025 06:02 PM
To: Bharat Agrawal <bharat.agrawal@ansys.com>
Cc: hughd@google.com <hughd@google.com>; akpm@linux-foundation.org <akpm@linux-foundation.org>; rientjes@google.com <rientjes@google.com>; zhangyiru3@huawei.com <zhangyiru3@huawei.com>; liuzixian4@huawei.com <liuzixian4@huawei.com>; mhocko@suse.com <mhocko@suse.com>; wuxu.wu@huawei.com <wuxu.wu@huawei.com>; linux-fsdevel@vger.kernel.org <linux-fsdevel@vger.kernel.org>; linux-kernel@vger.kernel.org <linux-kernel@vger.kernel.org>; linux-api@vger.kernel.org <linux-api@vger.kernel.org>; linux-mm@kvack.org <linux-mm@kvack.org>; legion@kernel.org <legion@kernel.org>
Subject: Re: mlock ulimits for SHM_HUGETLB
 
[External Sender]

On Mon, May 19, 2025 at 12:04:58PM +0000, Bharat Agrawal wrote:
> Thanks Greg for the response. RHEL has not been very helpful. I'm not looking to ask for patches because of the old versions.
> These messages appear in production runs, raising concerns about possible failures. Thus, the question is: Can they be ignored safely?

Again, you are paying them for support for this, please use them, there
is nothing that the community can do to help out here, sorry.

greg k-h

Re: mlock ulimits for SHM_HUGETLB

[Michal Hocko]

Hi,
On Mon 19-05-25 10:21:17, Bharat Agrawal wrote:
> Hi all,
> 
> Could anyone please help comment on the risks associated with an
> application throwing the "Using mlock ulimits for SHM_HUGETLB is
> deprecated" message on RHEL 8.9 with 4.18.0-513.18.1.el8_9.x86_64
> Linux kernel?

This is not RHEL specific behavior. The current Linus tree has the same
warning which has been added by 
: commit 2584e517320bd48dc8d20e38a2621a2dbe58fade
: Author: Ravikiran G Thirumalai <kiran@scalex86.org>
: Date:   Tue Mar 31 15:21:26 2009 -0700
: 
:     mm: reintroduce and deprecate rlimit based access for SHM_HUGETLB
: 
:     Allow non root users with sufficient mlock rlimits to be able to allocate
:     hugetlb backed shm for now.  Deprecate this though.  This is being
:     deprecated because the mlock based rlimit checks for SHM_HUGETLB is not
:     consistent with mmap based huge page allocations.
: 
:     Signed-off-by: Ravikiran Thirumalai <kiran@scalex86.org>
:     Reviewed-by: Mel Gorman <mel@csn.ul.ie>
:     Cc: William Lee Irwin III <wli@holomorphy.com>
:     Cc: Adam Litke <agl@us.ibm.com>
:     Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
:     Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

HTH
-- 
Michal Hocko
SUSE Labs