linux-kernel - Re: Page migration issue with UBIFS

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Message-ID: <20160315153744.GB28522@infradead.org>
Date:	Tue, 15 Mar 2016 08:37:44 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	Richard Weinberger <richard@....at>
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

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.