linux-kernel - Re: Page migration issue with UBIFS

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Message-ID: <20160315154708.GC16462@node.shutemov.name>
Date:	Tue, 15 Mar 2016 18:47:08 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Richard Weinberger <richard@....at>
Cc:	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 04:25:50PM +0100, Richard Weinberger wrote:
> Kirill,
> 
> Am 15.03.2016 um 16:17 schrieb Kirill A. Shutemov:
> > On Tue, Mar 15, 2016 at 03:16:11PM +0100, Richard Weinberger wrote:
> >> Hi!
> >>
> >> We're facing this issue from 2014 on UBIFS:
> >> http://www.spinics.net/lists/linux-fsdevel/msg79941.html
> >>
> >> So sum up:
> >> UBIFS does not allow pages directly marked as dirty. It want's everyone to do it via UBIFS's
> >> ->wirte_end() and ->page_mkwirte() functions.
> >> This assumption *seems* to be violated by CMA which migrates pages.
> > 
> > I don't thing the CMA/migration is the root cause.
> > 
> > How did we end up with writable and dirty pte, but not having
> > ->page_mkwrite() called for the page?
> > 
> > Or if ->page_mkwrite() was called, why the page is not dirty?
> 
> Thanks for your quick response!
> 
> I also don't think that the root cause is CMA or migration but it seems
> to be the messenger.
> 
> Can you confirm that UBIFS's assumptions are valid?
> I'm trying to rule out possible issues and hunt down the root cause...

The assumption looks reasonable for me, but I am not confident enough to
"confirm" it.

-- 
 Kirill A. Shutemov