linux-kernel - Re: [RFC] mm: show message when updating min_free

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <52C5E3C2.6020205@intel.com>
Date:	Thu, 02 Jan 2014 14:10:10 -0800
From:	Dave Hansen <dave.hansen@...el.com>
To:	David Rientjes <rientjes@...gle.com>
CC:	linux-kernel@...r.kernel.org,
	Andrea Arcangeli <aarcange@...hat.com>,
	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	Michal Hocko <mhocko@...e.cz>
Subject: Re: [RFC] mm: show message when updating min_free_kbytes in thp

On 01/02/2014 01:58 PM, David Rientjes wrote:
> On Thu, 2 Jan 2014, Dave Hansen wrote:
> 
>>> min_free_kbytes may be updated during thp's initialization. Sometimes,
>>> this will change the value being set by user. Showing message will
>>> clarify this confusion.
>> ...
>>> -	if (recommended_min > min_free_kbytes)
>>> +	if (recommended_min > min_free_kbytes) {
>>>  		min_free_kbytes = recommended_min;
>>> +		pr_info("min_free_kbytes is updated to %d by enabling transparent hugepage.\n",
>>> +			min_free_kbytes);
>>> +	}
>>
>> "updated" doesn't tell us much.  It's also kinda nasty that if we enable
>> then disable THP, we end up with an elevated min_free_kbytes.  Maybe we
>> should at least put something in that tells the user how to get back
>> where they were if they care:
> 
> The default value of min_free_kbytes depends on the implementation of the 
> VM regardless of any config options that you may have enabled.  We don't 
> specify what the non-thp default is in the kernel log, so why do we need 
> to specify what the thp default is?

Let's say enabling THP made my system behave badly.  How do I get it
back to the state before I enabled THP?  The user has to have gone and
recorded what their min_free_kbytes was before turning THP on in order
to get it back to where it was.  Folks also have to either plan in
advance (archiving *ALL* the sysctl settings), somehow *know* somehow
that THP can affect min_free_kbytes, or just plain be clairvoyant.

This seems like a pretty straightforward way to be transparent about
what the kernel mucked with, and exactly how it did it instead of
requiring clairvoyant sysadmins.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/