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

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Date:	Fri, 17 Jun 2016 09:41:38 +0200
From:	Richard Weinberger <richard@....at>
To:	Andrew Morton <akpm@...ux-foundation.org>
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,
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	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()

Andrew,

Am 17.06.2016 um 01:11 schrieb Andrew Morton:
> 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?

Well, we simply don't know which filesystems are affected by similar issues.
JFFS2 is maybe also affected since it is not block based.
For UBIFS it also worked many years.

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

Can I add your Acked-by?

Thanks,
//richard