linux-ext4 - Re: [PATCH 4/4] block: Optionally snapshot page contents to provide stable pages during write

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Date:	Mon, 7 Jan 2013 12:44:36 -0800
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Cc:	axboe@...nel.dk, lucho@...kov.net, jack@...e.cz, ericvh@...il.com,
	viro@...iv.linux.org.uk, rminnich@...dia.gov, tytso@....edu,
	martin.petersen@...cle.com, neilb@...e.de, david@...morbit.com,
	Zheng Liu <gnehzuil.liu@...il.com>,
	linux-kernel@...r.kernel.org, hch@...radead.org,
	linux-fsdevel@...r.kernel.org, adilger.kernel@...ger.ca,
	bharrosh@...asas.com, jlayton@...ba.org,
	v9fs-developer@...ts.sourceforge.net, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 4/4] block: Optionally snapshot page contents to provide
 stable pages during write

On Fri, Dec 28, 2012 at 06:48:35AM +0900, OGAWA Hirofumi wrote:
> "Darrick J. Wong" <darrick.wong@...cle.com> writes:
> 
> >> I think this flag should be separated into "FS provide stable page" and
> >> "FS needs bounce buffer for stable page".
> >> 
> >> My fs (I guess btrfs also) provides stable page by better way, and
> >> doesn't need to wait writeback flags too. What needs is just to avoid
> >> those stable page stuff.
> >
> > How does your fs (are we talking about vfat?) provide stable pages?
> 
> Basically it copies the data to another page before modifying data only
> if page has writeback flag. (this is about new fs under development stage.)

Aha, we're talking about tux3.  Since (afaik) there aren't any other
filesystems requesting this flag and tux3 uses the device bdi, should I just
create a patch and send it to you so it'll be included when tux3 goes in?

--D

> 
> > btrfs creates its own bdi and doesn't set the "stable pages required"
> > flag, so it already skips all the stable page stuff.
> 
> I see.
> -- 
> OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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