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

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Date:	Wed, 15 Jan 2014 15:22:18 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	David Rientjes <rientjes@...gle.com>,
	Han Pingtian <hanpt@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...e.cz>,
	linux-mm@...ck.org, Dave Hansen <dave.hansen@...el.com>
Subject: Re: [RFC] mm: show message when updating min_free_kbytes in thp

On Tue, Jan 14, 2014 at 04:35:33PM -0800, Andrew Morton wrote:
> > Would it be overkill to save the kernel default both with and without thp 
> > and then doing a WARN_ON_ONCE() if a user-written value is ever less?
> 
> Well, min_free_kbytes is a userspace thing, not a kernel thing - maybe
> THP shouldn't be dinking with it.  What effect is THP trying to achieve
> and can we achieve it by other/better means?

It moved logic from hugeadm where few people knew about it to the
kernel. The value is related to anti-fragmentation. With the recommended
setting the probability of mixing pages of different mobility within a
single pageblock is reduced. Very very superficially, it reduces the
number of instances the mm_page_alloc_extfrag tracepoint is triggered
with parameters that are considered to be severely fragmenting.

-- 
Mel Gorman
SUSE Labs
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