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

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Message-ID: <alpine.DEB.2.02.1401021357360.21537@chino.kir.corp.google.com>
Date:	Thu, 2 Jan 2014 13:58:52 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Dave Hansen <dave.hansen@...el.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 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?
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