linux-ext4 - Re: Best way to pin a page in ext4?

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Date:	Wed, 17 Sep 2014 15:57:19 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Hugh Dickins <hughd@...gle.com>, Theodore Ts'o <tytso@....edu>,
	Andreas Dilger <adilger@...ger.ca>,
	linux-mm <linux-mm@...ck.org>, linux-ext4@...r.kernel.org
Subject: Re: Best way to pin a page in ext4?

On Tue, Sep 16, 2014 at 10:31:24PM -0500, Christoph Lameter wrote:
> On Tue, 16 Sep 2014, Hugh Dickins wrote:
> 
> > On the page migration issue: it's not quite as straightforward as
> > Christoph suggests.  He and I agree completely that mlocked pages
> > should be migratable, but some real-time-minded people disagree:
> > so normal compaction is still forbidden to migrate mlocked pages in
> > the vanilla kernel (though we in Google patch that prohibition out).
> > So pinning by refcount is no worse for compaction than mlocking,
> > in the vanilla kernel.
> 
> Note though that compaction is not the only mechanism that uses page
> migration.

Agreed, and not all migration paths check for mlocked iirc. ISTR it is
very much possible for mlocked pages to get migrated in mainline.
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