linux-kernel - Re: [PATCH 1/3] mm: Don't blindly assign fallback_migrate

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Message-Id: <20160616161121.35ee5183b9ef9f7b7dcbc815@linux-foundation.org>
Date:	Thu, 16 Jun 2016 16:11:21 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Richard Weinberger <richard@....at>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linux-mtd@...ts.infradead.org, hannes@...xchg.org,
	mgorman@...hsingularity.net, n-horiguchi@...jp.nec.com,
	mhocko@...e.com, kirill.shutemov@...ux.intel.com, hughd@...gle.com,
	vbabka@...e.cz, adrian.hunter@...el.com, dedekind1@...il.com,
	hch@...radead.org, linux-fsdevel@...r.kernel.org,
	boris.brezillon@...e-electrons.com,
	maxime.ripard@...e-electrons.com, david@...ma-star.at,
	david@...morbit.com, alex@...tthing.co, sasha.levin@...cle.com,
	iamjoonsoo.kim@....com, rvaswani@...eaurora.org,
	tony.luck@...el.com, shailendra.capricorn@...il.com
Subject: Re: [PATCH 1/3] mm: Don't blindly assign fallback_migrate_page()

On Thu, 16 Jun 2016 23:26:13 +0200 Richard Weinberger <richard@....at> wrote:

> While block oriented filesystems use buffer_migrate_page()
> as page migration function other filesystems which don't
> implement ->migratepage() will automatically get fallback_migrate_page()
> assigned. fallback_migrate_page() is not as generic as is should
> be. Page migration is filesystem specific and a one-fits-all function
> is hard to achieve. UBIFS leaned this lection the hard way.
> It uses various page flags and fallback_migrate_page() does not
> handle these flags as UBIFS expected.
> 
> To make sure that no further filesystem will get confused by
> fallback_migrate_page() disable the automatic assignment and
> allow filesystems to use this function explicitly if it is
> really suitable.

hm, is there really much point in doing this?  I assume it doesn't
actually affect any current filesystems?

[2/3] is of course OK - please add it to the UBIFS tree.