linux-kernel - Re: Page migration issue with UBIFS

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Message-ID: <56E8985A.1020509@nod.at>
Date:	Wed, 16 Mar 2016 00:18:50 +0100
From:	Richard Weinberger <richard@....at>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	"Kirill A. Shutemov" <kirill@...temov.name>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	David Gstir <david@...ma-star.at>,
	Dave Chinner <david@...morbit.com>,
	Artem Bityutskiy <dedekind1@...il.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Alexander Kaplan <alex@...tthing.co>
Subject: Re: Page migration issue with UBIFS

Am 15.03.2016 um 16:37 schrieb Christoph Hellwig:
> On Tue, Mar 15, 2016 at 04:32:40PM +0100, Richard Weinberger wrote:
>>> Or if ->page_mkwrite() was called, why the page is not dirty?
>>
>> BTW: UBIFS does not implement ->migratepage(), could this be a problem?
> 
> This might be the reason.  I can't reall make sense of
> buffer_migrate_page, but it seems to migrate buffer_head state to
> the new page.
> 
> I'd love to know why CMA even tries to migrate pages that don't have a
> ->migratepage method, this seems incredibly dangerous to me.

FYI, with a dummy ->migratepage() which returns only -EINVAL UBIFS does no
longer explode upon page migration.
Tomorrow I'll do more tests to make sure.

Thanks,
//richard